@database "Flash-Units" @node main "Flash Units" Notes on Electronic Flash Units and Strobe Lights Contents: @{" Chapter 1 " link "1"} About the Author & Copyright @{" Chapter 2 " link "2"} Introduction @{" Chapter 3 " link "3"} Electronic Flash Troubleshooting @{" Chapter 4 " link "4"} Xenon Strobe Design @{" Chapter 5 " link "5"} Nifty Strobe Circuit Schematics and Notes @{" Chapter 6 " link "6"} Complete Strobe Schematics @{" Chapter 7 " link "7"} Items of Interest @endnode @node 2 "Chapter 2) Introduction" @{" 2.1 " link "2.1"} Electronic flash fundamentals @{" 2.2 " link "2.2"} Xenon strobe safety @{" 2.3 " link "2.3"} Safety guidelines @{" 2.4 " link "2.4"} Safe discharging of capacitors in electronic flash units @{" 2.5 " link "2.5"} Capacitor discharge tool @{" 2.6 " link "2.6"} Capacitor discharge indicator circuit @endnode @node 3 "Chapter 3) Electronic Flash Troubleshooting" @{" 3.1 " link "3.1"} Electronic flash problems @{" 3.2 " link "3.2"} Problems unique to battery or AC adapter powered electronic flash units @{" 3.3 " link "3.3"} Problems unique to AC line powered electronic flash units @{" 3.4 " link "3.4"} Problems common to all electronic flash units @{" 3.5 " link "3.5"} Electronic flash dead after long time in storage @endnode @node 4 "Chapter 4) Xenon Strobe Design" @{" 4.1 " link "4.1"} General strobe circuit design @{" 4.2 " link "4.2"} Strobe design parameters @{" 4.3 " link "4.3"} Some guidelines for designing small xenon strobes @{" 4.4 " link "4.4"} Transformers for low voltage powered strobe invertors @endnode @node 5 "Chapter 5) Nifty Strobe Circuit Schematics and Notes" @{" 5.1 " link "5.1"} Converting a pocket camera strobe into a repeating strobe @{" 5.2 " link "5.2"} Strobe design for multiple flashing @{" 5.3 " link "5.3"} Repeating strobe trigger generators @{" 5.4 " link "5.4"} Repeating trigger using 555 timer @{" 5.5 " link "5.5"} Repeating trigger using neon tube (indicator lamp) @{" 5.6 " link "5.6"} Relaxation oscillator operation @{" 5.7 " link "5.7"} Optoisolated remote trigger from low voltage logic or signal @{" 5.8 " link "5.8"} Optoisolated remote trigger operation @{" 5.9 " link "5.9"} Strobe systems with multiple flashheads @{" 5.10 " link "5.10"} Kevin's Super Strobomatic @{" 5.11 " link "5.11"} Tiny tiny invertor design @{" 5.12 " link "5.12"} Light beam triggered strobe circuit @endnode @node 6 "Chapter 6) Complete Strobe Schematics" @{" 6.1 " link "6.1"} Photoflash circuit from Keystone pocket camera @{" 6.1.1 " link "6.1.1"} Keystone electronic flash operation @{" 6.1.2 " link "6.1.2"} Keystone electronic flash notes @{" 6.2 " link "6.2"} Photoflash circuit from Kodak pocket camera @{" 6.2.1 " link "6.2.1"} Kodak electronic flash operation @{" 6.2.2 " link "6.2.2"} Kodak electronic flash notes @{" 6.3 " link "6.3"} Line powered photoflash circuit @{" 6.3.1 " link "6.3.1"} Line powered photoflash operation @{" 6.3.2 " link "6.3.2"} Line powered photoflash notes @{" 6.4 " link "6.4"} Higher power photoflash with SCR trigger @{" 6.4.1 " link "6.4.1"} Higher power photoflash with SCR trigger operation @{" 6.4.2 " link "6.4.2"} Higher power photoflash with SCR trigger notes @{" 6.5 " link "6.5"} Vivitar Auto 253 electronic flash circuit @{" 6.5.1 " link "6.5.1"} Vivitar Auto 253 power supply @{" 6.5.2 " link "6.5.2"} Vivitar Auto 253 power supply operation @{" 6.5.3 " link "6.5.3"} Vivitar Auto 253 exposure control circuit @{" 6.5.4 " link "6.5.4"} Vivitar Auto 253 exposure control operation @{" 6.5.5 " link "6.5.5"} Vivitar Auto 253 general notes @{" 6.6 " link "6.6"} High power (laser pump) strobe circuit @{" 6.6.1 " link "6.6.1"} High power (laser pump) strobe operation @{" 6.6.2 " link "6.6.2"} High power (laser pump) strobe notes @{" 6.7 " link "6.7"} Simple commercial timing light @{" 6.7.1 " link "6.7.1"} Timing light operation @{" 6.8 " link "6.8"} Variable intensity variable frequency stroboscope @endnode @node 7 "Chapter 7) Items of Interest" @{" 7.1 " link "7.1"} Why do roulette wheels sometimes appear to spin backward? @{" 7.2 " link "7.2"} Kevin attempts to abuse a strobe @{" 7.3 " link "7.3"} Parts suppliers @endnode @node 1 "Chapter 1) About the Author & Copyright" Author: Samuel M. Goldwasser E-Mail: sam@stdavids.picker.com Corrections/suggestions: [Feedback Form] [mailto] Copyright (c) 1996 All Rights Reserved Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. This document converted to AmigaGuide format by Mike Fuller 26-7-96 ----------------------------------------------------------------------------- @endnode @node 2.1 "Electronic flash fundamentals" All modern electronic flash units (often called photographic strobes) are based on the same principles of operation whether of the subminiature variety in a disposable pocket camers or high quality 35 mm camera, compact separate hot shoe mounted unit, or the high power high performance unit found in a photo studio 'speed light'. All of these use the triggered discharge of an energy storage capacitor through a special flash tube filled with xenon gas at low pressure to produce a very short burst of high intensity white light. The typical electronic flash consists of four parts: (1) power supply, (2) energy storage capacitor, (3) trigger circuit, and (4) flash tube. An electronic flash works as follows: 1. The energy storage capacitor connected across the flash tube is charged from a 300V (typical) power supply. This is either a battery or AC adapter operated invertor (pocket cameras and compact strobes) or an AC line operated supply using a power transformer or voltage doubler or tripler (high performance studio 'speed' lights). These are large electrolytic capacitors (200-1000+ uF at 300+ V) designed specifically for the rapid discharge needs of photoflash applications. 2. A 'ready light' indicates when the capacitor is fully charged. Most monitor the voltage on the energy storage capacitor. However, some detect that the invertor or power supply load has decreased indicating full charge. 3. Normally, the flash tube remains non-conductive even when the capacitor is fully charged. 4. A separate small capacitor (e.g., .1 uF) is charged from the same power supply to generate a trigger pulse. 5. Contacts on the camera's shutter close at the instant the shutter is fully open. These cause the charge on the trigger capacitor to be dumped into the primary of a pulse transformer whose secondary is connected to a wire, strip, or the metal reflector in close proximity to the flash tube. 6. The pulse generated by this trigger (typically around 4-10 KV depending on the size of the unit) is enough to ionize the xenon gas inside the flash tube. 7. The xenon gas suddenly becomes a low resistance and the energy storage capacitor discharges through the flash tube resulting in a short duration brilliant white light. The energy of each flash is roughly equal to 1/2*C*V^^2 in watt-seconds (W-s) where V is the value of the energy storage capacitor's voltage and C is its capacitance. Not quite all of the energy in the capacitor is used but it is very close. The energy storage capacitor for pocket cameras is typically 100-400 uF at 330 V (charged to 300 V) with a typical flash energy of 10 W-s. For high power strobes, 1000s of uF at higher voltages are common with maximum flash energies of 100 W-s or more. Another important difference is in the cycle time. For pocket cameras it may be several seconds - or much longer as the batteries run down. For a studio 'speed light', fractional second cycle times are common. Typical flash duration is much less than a millisecond resulting in crystal clear stop action photographs of almost any moving subject. On cheap cameras (and probably some expensive ones as well) physical contacts on the shutter close the trigger circuit precisely when the shutter is wide open. Better designs use an SCR or other electronic switch so that no high voltage appears at the shutter contacts (or hot shoe connector of the flash unit) and contact deterioration do to high voltage sparking is avoided. Note that for cameras with focal plane shutters, the maximum shutter speed setting that can be used (X-Sync) is typically limited to 1/60-1/120 of a second. The reason is that for higher shutter speeds, the entire picture is not exposed simultaneously by the moving curtains of the focal plane mechanism. Rather, a slit with a width determined the by the effective shutter speed moves in front of the film plane. For example, with a shutter speed setting of 1/1000 of a second, a horizontally moving slit would need to be about 1/10 of an inch wide for a total travel time of 1/60 of a second to cover the entire 1.5 inch wide 35 mm frame. Since the flash duration is extremely short and much much less than the focal plane curtain travel time, only the film behind the slit would be exposed by an electronic flash. For shutter speed settings longer than the travel time, the entire frame is uncovered when the flash is triggered. See the @{"schematics" link "6"} sections for typical circuit configurations of both battery and line powered electronic flash units of various sizes. Red-eye reduction provides a means of flashing the lamp twice in rapid succession. The idea is that the pupils of the subjects' eyes close somewhat due to the first flash resulting in less red-eye - reflected imaging of the inside of the eyeball - in the actual photograph. Automatic electronic flash units provide an optical feedback mechanism to sense the amount of light actually reaching the subject. The flash is then aborted in mid stride once the proper exposure has been made. This means that the flash duration will differ depending on exposure - typically from 1 ms at full power to 20 us or less at close range. Inexpensive automatic flash units just short across the flashlamp with an SCR or second internal 'quench' tube (an internal small xenon tube that looks like an oversize neon indicator lamp) triggered by a photosensor. With these units, the same amount of energy is used regardless of how much light is actually required and thus low and high intensity flashes drain the battery by the same amount - and require the same cycle time. The excess energy is wasted. Note that it is not the distance to the subject that matters but the amount of total light energy reflected back to the sensor. The travel time of the light has nothing to do with controlling exposure. More sophisticated units use something like a Gate Turnoff Thyristor (GTO) to actually interrupt the flash discharge at the proper instant. These use only as much energy as needed and the batteries last much longer since most flash photographs do not require maximum power. Furthermore, when using low power flashes, the cycle time is effectively zero since the main energy storage capacitor does not discharge significantly. Therefore, multiple shots can be taken in rapid succession. Failure of red-eye reduction or the automatic exposure control circuits will probably require a schematic to troubleshoot unless tests for bad connections or shorted or open components identify specific problems. However, some of these use fairly simple circuits with mostly standard components and can be traced without too much difficulty. Remotely triggered 'fill flashes' use a photocell or photodiode to fire an SCR (or light activated SCR) which emulates the camera shutter switch closure for the flash unit being controlled. There is little to go wrong with these devices. ----------------------------------------------------------------------------- @endnode @node 2.2 "Xenon strobe safety" There are two potential hazards in dealing with the innards of electronic flash and other xenon strobe equipment: 1. The energy storage capacitor. Even on small pocket camera electronic flash units, these are rated at 100-400 uF at 330 VDC. This is 5-20 W-s which is enough to kill you under the right (wrong?) conditions. Hot shoe or side mounted electronic flash units have energy storage capacitors which are usually larger - typically 300-1000 uF or more. High performance studio speed lights may have 10 times this capacity and at much higher voltages resulting in even greater energy storage. Xenon strobes for pumping of solid state laser rods and other industrial and scientific applications may use many KV power supplies with 1000s of W-s energy storage capacitors - touch one of these and you will be but a puff of vapor in the wind... High voltage with high energy storage is an instantly deadly combination. Treat all of these capacitors - even those in tiny pocket cameras with respect. Always confirm that they are discharged before even thinking about touching anything. On larger systems especially, install a shorting jumper after discharging just to be sure - capacitors have been known to recover a portion of their original charge without additional power input. Better to kill the power supply than yourself if you forget to remove it when powering up. 2. Line connected (no power transformer) have all the dangers associated with AC line power in addition to the large power supply and energy storage capacitors. Always use an isolation transformer when probing line connected systems. However, keep in mind that the power supply filter capacitors and energy storage capacitors remain just as deadly. ----------------------------------------------------------------------------- @endnode @node 2.3 "Safety guidelines" These guidelines are to protect you from potentially deadly electrical shock hazards as well as the equipment from accidental damage. Note that the danger to you is not only in your body providing a conducting path, particularly through your heart. Any involuntary muscle contractions caused by a shock, while perhaps harmless in themselves, may cause collateral damage - there are many sharp edges inside this type of equipment as well as other electrically live parts you may contact accidentally. The purpose of this set of guidelines is not to frighten you but rather to make you aware of the appropriate precautions. Electronic construction, testing, and troubleshooting can be fun and rewarding and economical. Just be sure that it is also safe! o Don't work alone - in the event of an emergency another person's presence may be essential. o Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system. o Wear rubber bottom shoes or sneakers. o Wear eye protection - large plastic lensed eyeglasses or safety goggles. o Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts. o Set up your work area away from possible grounds that you may accidentally contact. o Know your equipment: TVs and monitors may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Microwave ovens use the chassis as ground return for the high voltage. In addition, do not assume that the chassis is a suitable ground for your test equipment! o If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood. o If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 10-50 ohms/V approximate value (e.g., for a 200 V capacitor, use a 2K-10K ohm resistor). Monitor while discharging and/or verify that there is no residual charge with a suitable voltmeter. o Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations. o If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand. o Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the power supply section of a TV or monitor can be tested for short circuits with an ohmmeter. o Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) is not an isolation transformer! The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but will not protect you from shock from many points in a line connected TV or monitor, electronic flash or strobe, or the high voltage side of a microwave oven, for example. (Note however, that, a GFCI may nuisance trip at power-on or at other random times due to leakage paths (like your scope probe ground) or the highly capacitive or inductive input characteristics of line powered equipment.) A fuse or circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. However, these devices may save your scope probe ground wire should you accidentally connect it to a live chassis. o Don't attempt repair work, construction, or testing when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity. o Finally, never assume anything without checking it out for yourself! Don't take shortcuts! ----------------------------------------------------------------------------- @endnode @node 2.4 "Safe discharging of capacitors in electronic flash units" A working electronic flash or strobe may discharge its capacitors fairly quickly when it is shut off but most DO NOT do this. Furthermore, do not assume that triggering the flash fully discharges either the power supply filter or main energy storage capacitors fully - especially if it is a sophisticated automatic unit. The main filter capacitors in the low voltage power supply may have bleeder resistors to drain their charge relatively quickly - but resistors can fail. Don't depend on them. For battery powered equipment in particular, efforts may have been made NOT to bleed the energy storage capacitor to conserve on battery power should another shot be desired at a future time. Some units even keep the flash fully charged when supposedly turned off! The technique I recommend is to use a high wattage resistor of about 5 to 50 ohms/V of the working voltage of the capacitor. This will prevent the arc-welding associated with screwdriver discharge but will have a short enough time constant so that the capacitor will drop to a low voltage in at most a few seconds (dependent of course on the RC time constant and its original voltage). Then check with a voltmeter to be double sure. Better yet, monitor while discharging. Obviously, make sure that you are well insulated! For the power supply filter capacitors or main energy storage capacitors, which might be 400 uF at 350 V, a 2 K ohm 25 W resistor would be suitable. RC=.8 second. 5RC=4 seconds. A lower wattage resistor (compared to that calculated from V^^2 / R) can be used since the total energy stored in the capacitor is not that great (but still potentially lethal). The discharge tool and circuit described in the next two sections can be used to provide a visual indication of polarity and charge for TV, monitor, SMPS, power supply filter capacitors and small electronic flash energy storage capacitors, and microwave oven high voltage capacitors. Reasons to use a resistor and not a screwdriver to discharge capacitors: 1. It will not destroy screwdrivers and capacitor terminals. 2. It will not damage the capacitor (due to the current pulse). 3. It will reduce your spouse's stress level in not having to hear those scary snaps and crackles. ----------------------------------------------------------------------------- @endnode @node 2.5 "Capacitor discharge tool" A suitable discharge tool for each of these applications can be made as quite easily. The capacitor discharge indicator circuit described below can be built into this tool to provide a visual display of polarity and charge (not really needed for CRTs as the discharge time constant is virtually instantaneous even with a multi-M ohm resistor. o Solder one end of the appropriate size resistor (for your application) along with the indicator circuit (if desired) to a well insulated clip lead about 2-3 feet long. For safety reasons, these connections must be properly soldered - not just wrapped. o Solder the other end of the resistor (and discharge circuit) to a well insulated contact point such as a 2 inch length of bare #14 copper wire mounted on the end of a 2 foot piece of PVC or Plexiglas rod which will act as an extension handle. o Secure everything to the insulating rod with some plastic electrical tape. This discharge tool will keep you safely clear of the danger area. Again, always double check with a reliable voltmeter or by shorting with an insulated screwdriver! ----------------------------------------------------------------------------- @endnode @node 2.6 "Capacitor discharge indicator circuit" Here is a suggested circuit which will discharge the high voltage power supply filter capacitors and main energy storage capacitors of most types of electronic flash units and strobe lights. This circuit can be built into the discharge tool described above. A visual indication of charge and polarity is provided from maximum input down to a few volts. The total discharge time is approximately 1 second per 100 uF of capacitance (5RC with R = 2 K ohms). Safe capability of this circuit with values shown is about 500 V and 1000 uF maximum. Adjust the component values for your particular application. (Probe) <-------+ In 1 | / \ 2 K, 25 W Unmarked diodes are 1N400X (where X is 1-7) / or other general purpose silicon rectifiers. \ | +-------+--------+ __|__ __|__ | _\_/_ _/_\_ / | | \ 100 ohms __|__ __|__ / _\_/_ _/_\_ | | | +----------+ __|__ __|__ __|__ __|__ Any general purpose LED type _\_/_ _/_\_ _\_/_ LED _/_\_ LED without an internal resistor. | | | + | - Use different colors to indicate __|__ __|__ +----------+ polarity if desired. _\_/_ _/_\_ | In 2 | | | >-------+-------+--------+ (GND Clip) The two sets of 4 diodes will maintain a nearly constant voltage drop of about 2.8-3 V across the LED+resistor as long as the input is greater than around 20 V. NOTE: this means that the brightness of the LED is NOT an indication of the value of the voltage on the capacitor until it drops below about 20 volts. The brightness will then decrease until it cuts off totally at around 3 volts. Safety note: always confirm discharge with a voltmeter before touching any high voltage capacitors! ----------------------------------------------------------------------------- @endnode @node 3.1 "Electronic flash problems" A variety of failures are possible with electronic flash units. Much of the circuitry is similar for battery/AC adapter and line powered units but the power supplies in particular do differ substantially. Most common problems are likely to be failures of the power supply, bad connections, dried up or deformed energy storage or other electrolytic capacitor(s) and physical damage to the to the flashtube or other components. ----------------------------------------------------------------------------- @endnode @node 3.2 "Problems unique to battery or AC adapter powered electronic flash units" o Power source - dead or weak batteries or defective charging circuit, incorrect or bad AC adapter, worn power switch, or bad connections. Symptoms: unit is totally dead, intermittent, or has excessively long cycle time. Test and/or replace batteries. Determine if batteries are being charged. Check continuity of power switch or interlock and inspect for corroded battery contacts and bad connections or cold solder joints on the circuit board. o Power invertor - blown chopper transistor, bad transformer, other defective components. Symptoms: unit is totally dead or loads down power source when switched on (or at all times with some compact cameras). No high pitched audible whine when charging the capacitor. Regulator failure may result in excess voltage on the flash tube and spontaneous triggering or failure of the energy storage capacitor or other components. Test main chopper transistor for shorts and opens. This is the most likely failure. There is no easy way to test the transformer and the other components rarely fail. Check for bad connections. ----------------------------------------------------------------------------- @endnode @node 3.3 "Problems unique to AC line powered electronic flash units" WARNING: Line powered units often do not include a power transformer. Therefore, none of the circuitry is isolated from the AC line. Read, understand, and follow the safety guidelines for working on line powered equipment. Use an isolation transformer while troubleshooting. However, realize that this will NOT protect you from the charge on the large high voltage power supply and energy storage capacitors. Take all appropriate precautions. o Power source - dead outlet or incorrect line voltage. Symptoms: unit is totally dead, operates poorly, catches fire, or blows up. Spontaneous triggering may be the result of a regulator failure or running on a too high line voltage (if the unit survives). Test outlet with a lamp or circuit tester. Check line voltage setting on flash unit (if it is not too late!). o Power supply - bad line cord or power switch, blown fuse, defective rectifiers or capacitors in voltage doubler, defective components, or bad connections. Symptoms: unit is totally dead or fuse blows. Excessive cycle time. Test fuse. If blown check for shorted components like rectifiers and capacitors in the power supply. If fuse is ok, test continuity of line cord, power switch, and other input components and wiring. Check rectifiers for opens and the capacitors for opens or reduced value. ----------------------------------------------------------------------------- @endnode @node 3.4 "Problems common to all electronic flash units" WARNING: the amount of charge contained in the energy storage capacitor may be enough to kill - especially with larger AC line powered flash units and high power studio equipment. Read and follow all safety guidelines with respect to high voltage high power equipment. Discharge the energy storage capacitors fully (see the section: @{"Safe discharging of capacitors in electronic flash units" link "2.4"}) and then measure to double check that they are totally flat before touching anything. Don't assume that triggering a flash does this for you (especially for automatic units). For added insurance, clip a wire across the capacitor terminals while doing any work inside the unit. Better to blow a fuse than you if you should forget to remove it. o Energy storage capacitor - dried up or shorted, leaky or needs to be 'reformed'. Symptoms: reduced light output and unusually short cycle time may indicate a dried up capacitor. Heavy loading of power source with low frequency or weak audible whine may indicate a shorted capacitor. Excessively long cycle time may mean that the capacitor has too much leakage or needs to be reformed. Test for shorts and value. Substitute another capacitor of similar or smaller uF rating and at least equal voltage rating if available. Cycling the unit at full power several times should reform a capacitor that has deteriorated due to lack of use. If the flash intensity and cycle time do not return to normal after a dozen or so full intensity flashes, the capacitor may need to be replaced or there may be some other problem with the power supply. o Trigger circuit - bad trigger capacitor, trigger transformer, SCR (if used), or other components. Symptoms: energy storage capacitor charges as indicated by the audible invertor whine changing frequency increasing in pitch until ready light comes on (if it does) but pressing shutter release or manual test button has no effect. Spontaneous triggering may be a result of a component breaking down or an intermittent short circuit. Test for voltage on the trigger capacitor and continuity of the trigger transformer windings. Confirm that the energy storage capacitor is indeed fully charged with a voltmeter. o Ready light - bad LED or neon bulb, resistor, zener, or bad connections. Symptoms: flash works normally but no indication from ready light. Or, ready light on all the time or prematurely. Test for voltage on the LED or neon bulb and work backwards to its voltage supply - either the trigger or energy storage capacitor or invertor trans- former. In the latter case (where load detection is used instead of simple voltage monitoring) there may be AC across the lamp so a DC measurement may be deceptive.) o Trigger initiator - shutter contacts or cable. Symptoms: manual test button will fire flash but shutter release has no effect. Test for shutter contact closure, clean hot shoe contacts (if relevant), inspect and test for bad connections, test or swap cable, clean shutter contacts (right, good luck). Try an alternate way of triggering the flash like a cable instead of a the hot shoe. o Xenon tube - broken or leaky. Symptoms: energy storage and trigger capacitors charges to proper voltage but the manual test button does not fire the flash even though you can hear the tick that indicates that the trigger circuit is discharging. Inspect the flash tube for physical damage. Substitute another similar or somewhat larger (but not smaller) flash tube. A neon bulb can be put across the trigger transformer output and ground to see if it flashes when you press the manual test button shutter release. This won't determine if the trigger voltage high enough but will provide an indication that most of the trigger circuitry is operating. ----------------------------------------------------------------------------- @endnode @node 3.5 "Electronic flash dead after long time in storage" The unit may be totally dead or take so long to charge that you give up. For rechargeable units, try charging for the recommended time (24 hours if you don't know what it is). Then, check the battery voltage. If it does not indicate full charge (roughly 1.2 x n for NiCds, 2 x n for lead-acid where n is the number of cells), then the battery is likely expired and will need to be replaced. Even for testing, don't just remove the bad rechargeable batteries - replace them. They may be required to provide filtering for the power supply even when running off the AC line or adapter. For units with disposable batteries, of course try a fresh set but first thoroughly clean the battery contacts. See the sections on @{"batteries" link "3.2"} The energy storage capacitor will tend to 'deform' resulting in high leakage and reduced capacity after long non-use. However, you should still be able to hear the high pitched whine of the invertor. Where the unit shows no sign of life on batteries or AC, check for dirty switch contacts and bad internal connections. Electrolytic capacitors in the power supply and invertor may have deteriorated as well. If the unit simply takes a long time to charge, cycling it a dozen times should restore an energy storage capacitor that is has deformed but is salvageable. This is probably safe for the energy storage capacitor as the power source is current limited. However, there is no way of telling if continuous operation with the excessive load of the leaky energy storage capacitor will overheat power supply or invertor components. ----------------------------------------------------------------------------- @endnode @node 4.1 "General strobe circuit design" Here are some general guidelines for the design of a small (5-20 W-s) battery or line operated strobe. Most small flashlamps will operate on about 300 V (some as low as 250 - or less). If the flashlamp voltage is too low, the tube may not fire reliably or at all. If the flashlamp voltage is too high, spontaneous firing or damage and/or shortened flashlamp life due to excessive current may be the result. For power, you will need one of the following: 1. An inverter putting out about 300 VDC from your battery. Some of the cheap disposable cameras use as little as 1.5 V but don't expect too much battery life. There are zillions of simple inverter designs that will work using either discrete transistors or ICs with some minimal external components. The easiest way to obtain the inverter is to rip one out of a dead camera. Try garage sales, flea markets, thrift stores, or your Aunt Patty's attic. Typical cost for a cheap pocket camera from these sources is $.50 to $2. I don't know what your Aunt charges. Otherwise, you can build one easily. The only difficult part is finding a suitable transformer. They are easy to wind but don't expect great efficiency unless extreme care is taken in the design. For designing IC based DC-DC convertors, check out companies like Maxim and Linear Technology. These generally only require minimal external components like capacitors, diodes, and an inductor or two - but often no transformers. 2. A line operated voltage doubler for 110 VAC (just a rectifier for 220 VAC). When the peak voltage of the AC line is considered, these supplies will provide about 300-320 VDC. Common 1N4005/6/7 silicon rectifiers and small (e.g., 16 uF) 250 V electrolytics can be used for the doubler. Include a surge limiting resistor of about 22 ohms in the common as well as a current limiting resistor in the output (before the energy storage capacitor) to allow the flashlamp arc to quench (e.g., 100-1000 ohms). A line fuse, power switch, and power indicator are also essential. WARNING: the is a non-isolated line operated power supply - see safety guidelines. Do not connect triggering circuit directly - use capacitive or transformer coupling for safety. 3. An energy storage capacitor. A 200 uF capacitor charged to 320 V will give you 1/2*C*V*V = 10 W-s. Xenon flashlamps are rated in terms of both maximum flash energy and maximum average power (as well as others but for small strobe units - under 25 W-s or so - these are the most critical). These ratings should not be exceeded. For example, a tube rated at 20 W-s flash energy and 5 W average power could be flashed at most once every 4 seconds at a 20 W-s level or at most once every second at a 5 W-s level. Use a smaller capacitor for more frequent flashing. While photoflash rated capacitors are desirable, you should be able to get away with any good quality electrolytic for this type of modest power application. Note that the typical pocket camera flash uses a 100-400 uF capacitor and puts out quite a lot of light. 4. A trigger circuit. This is usually a HV pulse transformer into whose primary you discharge a small capacitor - .1 uF at 100-300 V is typical. The high voltage secondary is designed to put out 4-10 KV depending on flashlamp size and type. If the voltage of the trigger pulse is too low, the flashlamp may not fire or may fire erratically. If the trigger voltage is too high, there may be arcing to the flashlamp electrodes or other components resulting in possible damage. The trigger output is connected with a short wire to an electrode (wire, foil, or metal reflector) that is in close proximity to the xenon tube. The high voltage pulse ionizes the xenon gas mixture allowing the storage capacitor to discharge through it. Trigger transformers are available from places like Digikey and Mouser Electronics. These can also be constructed relatively easily. Though not very compact, a TV or monitor flyback or automotive ignition coil will also work as a trigger transformer. An SCR can be substituted for physical switch contacts where electronic control of the trigger is desired. For the battery powered unit, there is no issue of line isolation and the cathode of the SCR can be tied directly to the ground of your logic circuits. However, with the line operated strobe, isolation is essential for safety - use capacitor or transformer coupling, or an optoisolator. ----------------------------------------------------------------------------- @endnode @node 4.2 "Strobe design parameters" The common photographic strobe is not really designed for very short flash duration. While a typical electronic flash is much much shorter than one of those antique flash bulbs, it is still long compared to what is possible. Typical flash duration for a full power flash is under a millisecond with the range of automatic units going down to 20 microseconds or less for a minimum energy flash. One of those antique flash bulbs, on the other hand, had a flash duration of between 5 and 20 milliseconds. For most common photography, 1 millisecond or less is for all intents and purposes, instantaneous. However, if you want to freeze the blades of a rotating turbine or stop bullet in flight, even 20 microseconds is way too long. Some of the highest speed photographs using the light source to control exposure have been taken with spark gaps operating at many KV resulting in flash durations as low as fractions of microseconds. Even higher speed photography is possible using electronic image tubes. The first instants of conventional or nuclear detonations have been captured using this type of technology. For more information on high speed photography, see the classic works by Harold E. ("Doc") Edgerton. The following are just some general comments: Several design parameters influence flash intensity, duration, and maximum repeat rate. However, the relationships are not linear as a flashlamp is a gas discharge device with complex negative resistance characteristics. It is necessary to consult the flashlamp manufacturer's data sheets to do any detailed design. 1. Voltage. For a given energy, flash duration is inversely proportional to flash lamp voltage. The higher the voltage, the shorter the flash. 2. Capacitor size in uF. Total flash light output is proportional to the energy storage capacitor uF rating. However, both the peak intensity and the flash duration will increase with a larger capacitor. 3. Impedance of discharge path. Since the circuit when triggered is basically a capacitor discharging into a low impedance load, both the duration and peak intensity are affected. In addition, for higher capacity strobes especially, controlling this impedance is critical to achieving optimal light output as well as maximizing the life of the flash lamp. Excessive peak discharge current as well as reverse current due to overshoot and ringing reduces flash lamp life through damage to the electrodes. Too much instantaneous current and the flashlamp may explode. 4. Flashlamp design. The diameter, length, material, gas pressure, and electrode construction, etc. all affect the performance and power handling capabilities. 5. Cooling. Convection, forced air, and liquid (water or oil) cooling may be used. Dramatically higher average power is possible using liquid flow cooling if the flash lamp design will permit this. ----------------------------------------------------------------------------- @endnode @node 4.3 "Some guidelines for designing small xenon strobes" Flashlamp manufacturers publish very detailed data sheets for their products. For high power strobe design, all this information is essential. However, when building small strobe units (under 20 W-s), my general rules-of-thumb are: 1. Use a 250 - 350 V power supply for the energy storage capacitor. Depending on your application, this can be a battery or AC adapter powered invertor, transformer/rectifier power supply, a line operated voltage doubler for 110 VAC or a simple line rectifier and filter capacitor for 220 VAC. 2. Use a trigger transformer capable of 4-5 KV or more pulse output. The actual output trigger pulse voltage can be controlled by the voltage on the trigger capacitor. This is usually obtained from a voltage divider off of the energy storage capacitor. Too low and it won't flash reliably. Too high and arcing to nearby components may occur. 3. Follow the flashlamp manufacturer's ratings for maximum flash energy and average power. If you ripped the flashlamp out of something like a pocket camera, limit your flash energy to that provided by the capacitor contained in the unit or 10 W-s per inch of flashlamp length if the capacitor value is unknown. Limit the average power to this maximum energy every five seconds or the actual minimum full power cycle time if this known. 4. Use a photoflash rated capacitor if available but any good quality capacitor will probably work fine. No inductor is needed for these low power applications. For a 320 V power supply, flash energy is just about 5 W-s per 100 uF of energy storage capacitor rating. 5. Keep lead lengths between the energy storage capacitor and the flashlamp reasonably short (a few inches is fine). Minimize the length of the wire from the trigger transformer and make sure that it is well insulated and not in proximity to any other components. 6. Make sure human contact with all line connected and high voltage components is impossible during operation or at any time when a charge is present on the power supply or energy storage capacitors - by packaging everything in a plastic or grounded metal box, for example. 7. Always use capacitor, transformer, or optical isolation when triggering line powered strobe units from low voltage logic circuits or anything that a human may contact. This is recommended in general as it will assure that no high power transients find their way back into sensitive electronic circuits. 8. Don't neglect the essential power switch, fuse(s), and indicator lights. For logic controlled or computerized strobes, a mechanical test button using a hard set of contacts (i.e., across the SCR) is highly desirable. ----------------------------------------------------------------------------- @endnode @node 4.4 "Transformers for low voltage powered strobe invertors" It is usually not possible to determine all parameters of the invertor transformer when reverse engineering pocket camera strobes. (The following is from: Kevin Horton (khorton@tech.iupui.edu)) This is always the kicker. I have devoting heavy amounts of time into figuring out how these transformers work. They are very, very special. nothing else will work in their place, or if it does, it'll be woefully inefficient. They are usually .4" or so cubed, but may be larger. The gap on the core seems to be pretty critical- it limits the overall current that the circuit will draw. In one particular strobe I disassembled, they had a 100 pf cap coming from the output of the HV winding directly tied to the base of the drive transistor! I finally figured out why: it controlled the frequency vs voltage of the oscillator, hence giving it more current as it was completing a charging cycle! I've disassembled many of these small transformers. Unlike most ferrite transformers, these are usually held together by dipping them in wax, rather than varnish. Some transformers have the primaries wound on the core, while others have it on the outside. I haven't figured out exactly why this is. However, one one transformer I took apart, the feedback and drive windings were wound on the core; bifilar. The feedback was 11 turns, while the primary was 10. Both were #24. On top of that was thousands of turns of #40 or so wire. It seems that the small sizes play a part in the efficiency of these transformers; since the magnetic field is contained in such a small core area, the losses are small. ----------------------------------------------------------------------------- @endnode @node 5.1 "Converting a pocket camera strobe into a repeating strobe" The little inverter in those units cannot put out enough power to charge the normal energy storage capacitor any faster. It is quite easy to replace the inverter with a voltage doubler off the AC line (with a current limiting resistor! WARNING: non-isolated power supply). Using a smaller energy storage capacitor would also permit a much higher flash rate at reduced brightness and this would prolong the life of the flashtube as well. With too high a repetition rate at high power, the problem is heat dissipation in the tube. Above a flash rate of once every couple of seconds, your poor little tube will degrade fairly quickly and it may not turn off properly as well due to overheating of the electrodes. It will probably be necessary to use an SCR instead of a set of switch contacts to allow triggering from a 555 timer or other logic level input. For a basic constant frequency strobe, a relaxation oscillator using a unijunction transistor or neon lamp, an astable multivibrator built from a couple of general purpose transistors, or a counter operated from the AC line zero crossings or a crystal oscillator would be perfectly adequate. However, a very simple repeating trigger can be made from a motor driven cam operated microswitch. Using a variable speed motor would implement a basic adjustable frequency stroboscope with no additional electronic components. In any case, if you retain the invertor, use an AC adapter or other power supply instead of batteries for testing at least. Otherwise, let me know which battery company's stock I should buy! ----------------------------------------------------------------------------- @endnode @node 5.2 "Strobe design for multiple flashing" These are often seen in safety related applications - warning lights, for example, where a typical cycle might be two flashes .2 seconds apart with a .8 second dead time. Here is one approach to designing a strobe that will double (or multiple) flash from a battery powered invertor of limited capacity. Charge a large buffer storage capacitor from the DC-DC converter, then have its output feed a smaller flash energy storage capacitor through a resistor small enough to give you a fast recharge but large enough to allow the flashlamp arc to quench. Building the DC-DC converter is pretty easy and you should be able to make it run off of a battery without any problem. You can use a simple power oscillator feeding a home-wound step-up transformer. With the energy buffer, the invertor only needs to satisfy the average power requirements of the multi-flash cycle. See the section: @{"General strobe circuit design" link "4.1"} For example, a small unit using a 100 uF 330 V capacitor for the flash could use a 1000 uF cap. for buffer storage separated by a 250 ohm power resistor. That would provide a 100 ms or so cycle time. The 1000 uF cap provides a reservoir between the relatively low power DC-DC converter and the tube as long as you do not flash too quickly - faster than your DC-DC converter can keep up. This should be much easier than trying to interrupt the 10s-100s of amperes of current flowing in the tube during the flash. ----------------------------------------------------------------------------- @endnode @node 5.3 "Repeating strobe trigger generators" Here are two simple circuits for generating a continuously repeating strobe trigger. It is assumed that the power supply and xenon tube can handle the average power requirements for the minimum desired cycle time. Inadequate energy storage capacitor charging power will result in erratic or reduced intensity flashing. Excessive heating caused by too high a repeat rate may lead to damage to circuit components and/or the flashlamp or may result in the arc not quenching properly between flashes. Inadequate trigger charging power (RC time constant too long) will result in missed or erratic triggering. ----------------------------------------------------------------------------- @endnode @node 5.4 "Repeating trigger using 555 timer" This is a common 555 timer operated in astable mode. For a detailed description of the circuit operation, see the 555 timer datasheet any databook which includes the 555 timer chip. Component values have been selected to cover a range of about 1 to 10 seconds between flashes. +--+ | V R1 R2 +5 to o--+-----------------+---+-+/\/\---+-/\/\--+ +15 VDC | | | 200K 5K | | | | | | +------|---|------+ | _|_ C3 | |8 |4 | | --- .1 uF | +---------+ | | | | 2| VCC R |3 | | | +-----+---|TR Q|--------------|---------o Trig+ | | | U1 |7 | | | _|_ C1 | 555 DIS|--------------+ | --- 100 5| |6 | | (Positive edge trigger | | uF +---|CV G THR|---+ | to optoisolator or | | _|_ +---------+ | | isolated SCR gate.) | | --- C2 |1 | | | | | .01 uF | | R4 | GND o--+----+-----+--------+ +---/\/\---+---------o Trig- 5K ----------------------------------------------------------------------------- @endnode @node 5.5 "Repeating trigger using neon tube (indicator lamp)" This is a simple relaxation oscillator using a common NE2 neon indicator lamp. As drawn, the repeat rate should be adjustable from about .1 to 10 Hz. Adjust component values for your particular needs. (NOTE: use of audio taper potentiometer would help to linearize the adjustment range.) +---+ +150 R1 R2 V | VDC o----/\/\----/\/\/-+----+--------+ +------o Out+ 50K 20M | | | | +++ | | |o| NT1 | | |o| NE2 __|__ SCR1 | +++ _\_/_ M21C, FOR3G, | | C2* / | TIC106 typ. +_|_ C1 +----||---+---' | ___ 2 uF | .01 uF | | - | / 400 V / | (To trigger | \ R3 \ R4 | capacitor/ | / 10K / 1K | transformer) | \ \ | | | C3* | | Return o--------------------+--------+----||---+------+------o Out- .01 uF 400 V ----------------------------------------------------------------------------- @endnode @node 5.6 "Relaxation oscillator operation" The neon indicator, NT1, is a negative resistance device. It becomes conductive when the voltage across it exceeds about 90 V but then only requires about 60 V to maintain conduction. This circuit has an RC network formed by R1, R2, and C1. C1 charges through R1 and the repeat rate adjustment potentiometer, R2. When its voltage exceeds the NE2 breakdown voltage, C1 discharges through NT1 resulting on a pulse on R3 coupled by C2 to the gate of SCR1. The SCR fires and discharges the trigger capacitor (not shown) into the trigger transformer of the strobe firing circuit. Once the voltage across NT1 has decreased below about 60 V, it turns off and the cycle repeats. Since the voltage across NT1 is swinging between about 60 and 90 V (out of 150 VDC total), the repeat frequency should be between 4 and 5 times 1/(RC). It is assumed that SCR1 (Out+/-) takes the place of the shutter contacts, is the SCR, or in parallel with the SCR shown in the strobe circuits shown elsewhere in this document. For other values of VPP between about 100 and 300 V, adjust resistance values appropriately. Note that C3* and C4* are essential to provide safety isolation for line powered strobes. ----------------------------------------------------------------------------- @endnode @node 5.7 "Optoisolated remote trigger from low voltage logic or signal" Here is a circuit for an optoisolated trigger interface. This will permit control of line-connected (non-isolated) strobes from logic or other lower voltage signals. This is probably the safest way to deal with the isolation and safety issues as the insulation resistance of typical optoisolators is several KV (7.5 KV for the specific part shown). This basic design would be suitable for a wide variety of applications requiring microprocessor, PIC, or PC control. A multiheaded strobe pulsing to a musical beat (high power color organ) could be implemented by triggering several strobe units from an audio amp's speaker output via audio filters of various cutoff or bandpass frequencies. VPP o | \ R3 / VPP>10V: R3~=(1K x VPP)-5K. (+5 to +10 V) \ VPP<10V: R3=1K, R4 not needed. IN1 (DC) o------+ / C1 | R1 | IN2 (AC) o--||--+--/\/\--+-------+ +-------+-----+ +----o Out+ .01 uF| 220 | | OPTO1 | | C2 | 1 uF | | | +--|-------|-+ / +_|_ | \ __|__ |__|__ |/ C| R4 \ ___ __|__ SCR1 R2 / D1 _/_\_ |_\_/_-> | | 5K / - | _\_/_ M21C, FOR3G, 1K \ 1N4148 | | | |\ E| | | / | TIC106 typ. | | +--|-------|-+ +-----+ | | | | |PC713V | | | | GND o-----+--------+-------+ Typ. +-------|-----+----+ | (To trigger | | | | capacitor/ | R5 \ C3_|_ | transformer) | 1K / --- | | \ 100| | | | pF | | +----------+--+----o Out- ----------------------------------------------------------------------------- @endnode @node 5.8 "Optoisolated remote trigger operation" The input signal may be DC coupled resulting is a high level triggering the strobe or AC coupled resulting in a positive edge trigger. R1 provides current limiting to the optoisolator's LED and R2 minimizes any possibility of electrical noise turning on the optoisolator. Change the values of R1 and R2 for a different input voltage range. D2 provides reverse voltage protection for the LED. For VPP greater than 10 V, the voltage divider formed by R3 and R4 charges C2 to about 5 V. This is the most common case where VPP is derived from the strobe power supply and is typically 300 V. The time constant for this RC network is under 5 ms so it will not affect high speed repeat operation. C2 assures that there will be enough current from the optoisolator to trigger SCR1 even with the high value resistor which may be used for R3 to minimize power dissipation with a large VPP. For a VPP of less than 10 V, the circuit can be simplified to just a current limiting resistor (leave out R4). When current flows through OPTO1's LED, it turns on the phototransistor which allows C2 to discharge into the gate of SCR1 which is connected to the trigger capacitor and transformer of the flashlamp firing circuit (not shown). To minimize the possibility of false triggering, locate the optoisolator circuit in close proximity to the SCR. R5 and C3 are included to reduce the SCR's sensitivity to any electrical noise pickup as well. VPP must be a positive DC voltage referenced to the terminal Out-. In most cases, this will be the energy storage capacitor's positive terminal. ----------------------------------------------------------------------------- @endnode @node 5.9 "Strobe systems with multiple flashheads" Have you seen the 'new' ball used for the New Year's celebration on top of the tower in Times Square? Is uses something like 144 computer controlled xenon lamps. Sort of gives you something to strive for! Two approaches can be taken in designing such systems depending on the needs. If only one flashlamp is to fire at any given time, a single energy storage capacitor can be shared by multiple flashlamps assuming the distance between it and any flashlamp is not excessive (probably less than a couple of feet). Alternatively, each flashlamp can be connected to its own energy storage capacitor fed through a current limiting resistor from one high capacity power supply. Hybrid systems using a combination of these techniques are also possible. In all cases, each flashlamp must have its own trigger transformer. An optoisolated SCR can then be controlled from a logic level signal - the output of a PC's parallel port or a dedicated bus. For long runs, use Schmitt Trigger gates or differential line drivers/receivers to prevent false triggering due to interference from the high voltage and high current pulses associated with each flashlamp's firing. ----------------------------------------------------------------------------- @endnode @node 5.10 "Kevin's Super Strobomatic" (The following is from: Kevin Horton (khorton@tech.iupui.edu)) I'm building a super strobe bar! It has 8 strobe tubes under computer control. (Actually a PIC processor, but hey, computer is a computer. I have all the stuff done except the control section, and I only have 2 of the 8 strobe units done due to the fact that I haven't found any more cheap cameras at the thrift store! (One Saturday morning's worth of garage sales and flea markets would remedy that! --- sam). It runs on 12 V, at up to 6 A, and can fire the tubes at a rate of about 8-10 times per second. The storage cap is a 210 uf, 330 V model; it gets to about 250 V to 300 V before firing; depending on how long it has had to charge. Because of this high speed, the tubes get shall we say, a little warm. (Well, maybe a lot warm --- sam). I have it set up at the moment driving two alternating 5 W-s tubes. I'm pumping them quite a bit too hard, as the electrodes start to glow after oh, about 5 seconds or so of continuous use. I know, a high class problem, indeed! My final assembly will have 8 tubes spaced about 8 inches apart on a 2x4, with a Plexiglass U-shaped enclosure with a nice 12 V fan blowing air through one end of the channel to cool the inverter and the tubes. Stay tuned. A [companion document] at this site includes schematics that provide some details of this design: Invertor High power 12 V to 300 V invertor for high repeat rate medium power strobes. Schematic in IFF format: @{"Inverter.iff" link "Inverter.iff/main"} Trigger Opto-isolated logic level trigger for general strobe applications. Schematic in IFF format: @{"Trigger.iff" link "Trigger.iff/main"} ----------------------------------------------------------------------------- @endnode @node 5.11 "Tiny tiny invertor design" (The following is from: Kevin Horton (khorton@tech.iupui.edu)) I have developed a cool little transformer circuit that seems to be very efficient. I built this inverter as tiny as I could make it. It runs off of 3V, and charges up a little 1 uf 250V cap all the way up in about 30 seconds; drawing about 5 to 8 mA in the process. The numbers by the windings tell the number of turns. The primary and feedback windings are #28, while the secondary is #46. Yes, #46! I could hardly tell what gauge it was, as it was almost too small to measure with my micrometer! It may be #44 or #45, but at these sizes, who knows? I used a trigger transformer for the wire. I used all the wire on it, to be exact; it all JUST fit on the little bobbin. The primary went on the core first, then the secondary, and finally the feedback winding. This order is very important. I used a ferrite bobbin and corresponding ferrite 'ring' that fit on it. The whole shebang was less than 1 cm in diameter, and about 3-5 mm high! I gave it a coat of wax to seal things up, and made the inverter circuit with surface-mount parts, which I then waxed onto the top. There are two wires in, and two wires out. It's enough to run a neon fairly brightly at 1.2 V, with a 3 ma current draw. Schematic in IFF format: @{"Teeny.iff" link "Teeny.iff/main"} Vcc >---+--------------+ T1 | 6T )|| \ #28 )|| +-------> HV output R1 / )||( 47K \ +---+ ||( / 2N4401 | ||( | |/ C ||( 450T | +--| Q1 ||( #46 | | |\ E ||( | | | ||( +--+ +--------+ ||( | | |17T )||( C1 _|_ | |#28 )|| +-------> HV return .001 uF --- | | )|| | +-----------+ | | Gnd >----+----------+ ----------------------------------------------------------------------------- @endnode @node 5.12 "Light beam triggered strobe circuit" Here, the intention is to trigger a strobe should a light beam be interrupted or completed. Any of the electronic flash schematics can be modified for this purpose. The circuit below should work for the detector. Its output may need to be put through one (light beam completed) or two (light beam interrupted) inverting Schmitt Trigger gates (e.g., 74LS14) to clean up its output and provide the proper polarity. It should be AC coupled to the gate of an SCR. The SCR will substitute for the camera's X-sync contacts and fire the strobe. Note that if this is a line operated unit, capacitor (or transformer) coupling is essential for providing the very important line isolation barrier absolutely required for safety. For the case where the strobe is supposed to fire when the light beam is interrupted, when the light beam is unbroken, the photodiode is illuminated providing current to keep the transistor on and its output is low. When the beam is broken, the output goes high, is cleaned up by the Schmitt Trigger gates creating a rising edge to provide a pulse to trigger the SCR. Any common IR or visible photodiode can be used for PD1. Sources include optoisolators, photosensors from dead VCRs, and optomechanical computer mice. Vcc >-------+---------+ | | +------o Out+ \ \ | / R1 / R3 | \ 3.3K \ 470 (1 or 2 Schmitt __|__ SCR1 / / Trigger Gates) _\_/_ M21C, FOR3G, | | +-----+ +-----+ C1 /| TIC106 typ. __|__ +---| ST1 |----| ST2 |---||---' | Light beam ---> _/_\_ Q1 | +-----+ +-----+ .001 uF | PD1 | B |/ C 600 V | +-------| 2N3904 | (To trigger | |\ E | capacitor/ \ | | transformer) / R2 | | \ 27K | | | | C2 | +---------+------------------------||-----+------o Out- _|_ .001 uF - 600 V Notes: 1. CAUTION: Capacitors provide needed isolation barrier for line connection electronic flash units. 2. For detecting a light beam being completed, an inversion is needed. Therefore, use an inverting Schmitt Trigger or a single 74LS14s invertor gate. 3. For detecting a light beam being interrupted, no inversion is needed. Therefore, use a non-inverting Schmitt Trigger or 2 74LS14s invertor gates. ----------------------------------------------------------------------------- @endnode @node 6.1 "Photoflash circuit from Keystone pocket camera" This schematic was traced from an electronic flash unit removed from an inexpensive pocket camera, a Keystone model XR308. Note that the ready light is not in the usual place monitoring the energy storage capacitor voltage. It operates on the principle that once nearly full charge is reached and the invertor is not being heavily loaded, enough drive voltage is available from an auxiliary winding on the invertor transformer to light the LED. It is also interesting that the trigger circuit dumps charge into the trigger capacitor instead of the other way around but the effect is the same. Invertor Flashtube +------------------------------+---------------------+--+--------+---+ | 1 K Ready LED | S1 Power | | | | | +--/\/\-----+--|<|-----+ | ______ On | +-+ T2 +-+ | BT1 _ | R1 | IL1 | | | \___| )||( | 3 V ___ | || +------|--/\/\/---+ | C1 | __ Off )||( +|FL1 2-AA _ | ||(2 .4 | R2 10 | Energy | | )||( _|_ ___ | || +-------------+ | Storage | +-------+---+ ||( | | | | | ||(5 .2 | | +| 280 uF | | ||( || | +---+ || +------+ | __|__ 330 V | S2 Fire -| ||( || | | ||(1 | | _____ | (Shutter) | +--|| | +---+ ||( | C3 | | | +-----+ Trigger || | 3)||( 142 -|47 uF | -| | | | || _ | <.1 )||( _|_ 6.3 | | | R1 \ _|_ C2 |_|_| )||( ___ V | | | 1M / --- .02 uF | +-+ || +-+ | | | | \ | 400 V -| C| 4 T1 6 | +| | | | / | | B|/ | | | D1 | | | | | +--| 2SD879 +--------------|<|--+----------------+-----+--------------+ | |\ Q1 | | HV Rect. | | E| | | | | +-------------+------|------------------+ | | +-------------------------+ ----------------------------------------------------------------------------- @endnode @node 6.1.1 "Keystone electronic flash operation" 1. The invertor boosts the battery voltage to about 300 V. This is rectified by D1 and charges the energy storage capacitor, C1. 2. The LED, IL1, signals ready by once C1 is nearly fully charged. 3. Pressing the shutter closes S2 which charges C2 from C1 through T2 generating a high voltage pulse (4-5KV) which ionizes the xenon gas in the flashlamp, FL1. 4. The energy storage capacitor discharges through the flashlamp. ----------------------------------------------------------------------------- @endnode @node 6.1.2 "Keystone electronic flash notes" 1. The invertor transformer winding resistances measured with a Radio Shack DMM. Primary resistance was below .1 ohms. 2. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.2 "Photoflash circuit from Kodak pocket camera" This schematic was traced from an electronic flash unit removed from an inexpensive Kodak pocket camera. Errors in transcription are possible. Designs similar to this are used by a wide variety of small photoflash units. D1 Flashlamp +------|>|-----+---------+---------------------------+ Invertor | HV Rect. | | FL1 | +------+--------------------+ | | C3 | | | Q1 | | | \ .047 +| | |C PNP | | | Energy / R3 +---||---+ Trigger _|_ \ \| (ECG12) | | | Storage \ 3.3M| | | | | / R1 |------------+ | | 200 uF / | +--+ | T2 || | \ 150 /| | | | +| 330 V | +--+oo+--+ || | | |E T1 || +-+ | | __|__ | | +--+ | || +--|| | | | ||(2 | | _____ C2 +-----+ IL1 | ||( || | +--||--+----+ ||( | | | | | NE2 | ||( || _ | | C1 1)||( 80 | | -| | | Ready +-+ ||( |_|_| | .33 <.1 )||( | | | \ | )||( | | )|| +-------+ | | / R2 | Shutter )||( | | +--+ ||(3 | | | | \ 20M |- )||( -| | | 4 ||( .2 | | | | / | S2 +-+ || +-+ | | | || +----+ | | | | | | | | | | 5 | | | | | +--------+ | +------------------------+ | | | | | | | +-----+---------+-----+---+-----------------+ | ___/ ____| | | | | | : | +------------------------||||------+ : S1 Power | | | |___/ _________| BT1 3V 2AA ----------------------------------------------------------------------------- @endnode @node 6.2.1 "Kodak electronic flash operation" 1. The invertor boosts the battery voltage to about 300 V. This is rectified by D1 and charges the energy storage capacitor, C2. 2. The trigger capacitor, C3, charges through R3 and T2. 3. The neon bulb, IL1, signals ready by flashing at about 6 Hz. 4. Pressing the shutter closes S2 which discharges C3 through T2 generating a high voltage pulse (4-5KV) which ionizes the xenon gas in the flashlamp, FL1. 5. The energy storage capacitor discharges through the flashlamp. ----------------------------------------------------------------------------- @endnode @node 6.2.2 "Kodak electronic flash notes" 1. Transistor was unmarked but ECG12 should be a suitable choice. 2. Resistances of T1 measured with Radio Shack DMM. 3. The power switch, S1, disconnects both the supply to the invertor and the return for the trigger to prevent accidental triggering with power off. 4. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.3 "Line powered photoflash circuit" Here is a sample schematic for a typical line operated medium power electronic flash unit. Cycle time is under 1 second. D1 R2 Flashlamp +---|>|---+--/\/\/--+---------+------+--------+-------------------+ | 1N4005 | 250 | | | | FL1 | | +| 10W | | | | | | _|_ C1 | \ +++ \ +| Power | ___ 25 uF | Energy / R6 |o| IL1 / R3 Trigger _|_ S1 | | 200 V | Storage \ 91K |o| NE2 \ 1.5M* | | | H __/ __| -| | 400 uF / +++ / T2 || | | R1 | +| 450 V | | Ready | || | N ---------/\/\---+ __|__ | | | C4 || +--|| | | 27 | _____ C3 +------+ +-----+--||--+ ||( || | AC Line | 5W +| | | | |.1 uF | ||( || _ | 115 VAC | _|_ C2 -| | | | +-+ ||( |_|_| | ___ 25 uF | \ \ | )||( | | | 200 V | / R7 / R4 | Shutter )||( | | -| | \ 180K \ 3M |- )||( -| | D2 | | / / | S2 +-+ || +-+ | +---|<|---+---------+ | | | | | | 1N4005 | | R5 | | | | | +---------+--/\/\---+-----+------+--------+ | Doubler | 1.5M* | | | +-----------------------------------+ ----------------------------------------------------------------------------- @endnode @node 6.3.1 "Line powered photoflash operation" 1. The doubler consisting of D1, D2, C1, and C2, boosts the AC line voltage to about 320 V. This charges the energy storage capacitor, C3 through R2. R1 limits inrush current to the doubler. 2. The trigger capacitor, C4, charges through R3, R5, and T2. 3. The neon bulb, IL1, signals ready by coming on when C3 is charged to about 270 V. 4. Pressing the shutter closes S2 which discharges C4 through T2 generating a high voltage pulse (4-5KV) which ionizes the xenon gas in the flashlamp, FL1. 5. The energy storage capacitor discharges through the flashlamp. R2 limits current from doubler to allow flashlamp arc to quench. ----------------------------------------------------------------------------- @endnode @node 6.3.2 "Line powered photoflash notes" 1. CAUTION: Line operated power supply is not isolated - use with care. Fuse and power-on indicator not shown. * R3 and R5 provide protection from line for trigger circuit - do not remove! 2. Flash energy is about 20 W-s. Adjust component values for desired application. 3. For rapid cycle times, make sure flashlamp is rated for adequate average power dissipation (e.g., 25 W for 1 second repeat). Forced air cooling may be required for sustained operation at full power. 4. Trigger transformer, T2, available from places like Digikey and Mouser. 5. Shutter contacts, S2, may be replaced with SCR for electronic control of flash trigger. 6. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.4 "Higher power photoflash with SCR trigger" Here is a sample schematic for a typical line operated moderately high power electronic flash unit. The power supply uses a tripler to generate approximately 420 V for the energy storage capacitor. An SCR allows a safely isolated logic or sensor signal to easily trigger the strobe. Cycle time is under 2 seconds. D3 R2 Flashlamp +-------+--|>|--/\/\--+----+------+--------+-------------------+ | |1N4007 270 | | | | FL1 | | | 2W | | | | | _|_ | | \ +++ \ +| /_\ D1 | | / R5 |o| IL1 / R3 _|_ |1N4007 | C3 | \ 91K |o| NE2 \ 1.5M Trigger | | | | | 500 uF | / +++ / || | | | 450 V | | | Ready | T2 || | +----+ +_|_ C2 +__|__ | | | C4 +--|| | | | ___ 22 uF _____ +------+ +-----+--||--+ ||( || | | | - | 450 V - | | | |.1 uF | ||( || _ | C1 _|_+ _|_ | | | | | +-+ ||( |_|_| 22 ___ /_\ D2 | | \ \ __|__ )||( | 450 V | - |1N4007 | | / R6 R4 / _\_/_ SCR1 )||( | | | | | \ 270K 1M \ / | TIC106 )||( -| | | | | / / | | +-+ +-+ | H >---+ +-------+---+---------+ | | | | | | | R1 | | | | | | | | | N >----------/\/\------+ +----+---------+-----+--+---+--------+---+ 22 | | Tripler C5* | | Trigger + >---||---+ | .001 uF | 600 V | | C6* | Trigger - >---||---------+ .001 uF 600 V ----------------------------------------------------------------------------- @endnode @node 6.4.1 "Higher power photoflash with SCR trigger operation" 1. The tripler consisting of D1, D2, D3, C1, and C2, boosts the AC line voltage to about 420 V. This charges the energy storage capacitor, C3 through R2. R1 limits inrush current to the tripler. 2. The trigger capacitor, C4, charges through R3 and T2. 3. The neon bulb, IL1, signals ready by coming on when C3 is charged to about 360 V. 4. Applying a positive edge between Trigger + and - turns on the SCR which discharges C4 through T2 generating a high voltage pulse (5-8KV) which ionizes the xenon gas in the flashlamp, FL1. 5. The energy storage capacitor discharges through the flashlamp. R2 limits current from doubler to allow flashlamp arc to quench. ----------------------------------------------------------------------------- @endnode @node 6.4.2 "Higher power photoflash with SCR trigger notes" 1. CAUTION: Line operated power supply is not isolated - use with care. Fuse and power-on indicator not shown. * C5 and C6 provides protection from the line for trigger circuit - DO NOT REMOVE! As an added safety precaution, the use of an optoisolator or optoisolated SCR is recommended for the trigger circuit. 2. Flash energy is about 45 W-s. Adjust component values for desired application. 3. For rapid cycle times, make sure flashlamp is rated for adequate average power dissipation (e.g., 50 W for 1 second repeat). Forced air cooling may be required for sustained operation at full power. 4. Trigger transformer, T2, available from places like Digikey and Mouser. 5. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.5 "Vivitar Auto 253 electronic flash circuit" The Vivitar Auto 253 is a typical small inexpensive automatic electronic flash. As is typical of these designs, the flashlamp is paralleled with a quenchtube. This is a small discharge tube that looks something like an oversized neon indicator light (but probably xenon filled). The quenchtube is triggered at a time after the main flashlamp fires which is determined by the light reflected from the subject and terminates the flash when adequate exposure has been achieved. The actual trigger circuit using an SCR to pulse a trigger transformer applying a 4-5 KV pulse to a foil wrapping on the quenchtube. Typical flash duration for small automatic electronic flash units vary from about 1/50,000 second for a minimum energy (closeup) flash to 1/1000 second for a maximum energy (distant subject or manual) flash. The power supply portion of this unit is interesting as well. It can operate on either AC (220 V, it would seem from the circuit) or a 9 V battery. For AC, a simple half wave rectifier produces about 320 VDC needed by the flashlamp. On DC, it uses an invertor that operates on a 9 V battery rather than the 3 V which is typical of many cheap pocket cameras. This results in a fairly rapid cycle time of about 2 seconds. The ready light looks like an ordinary NE2 neon bulb but must have a different gas mixture as it does not turn on until nearly full charge is reached on the energy storage capacitor. There appears to be no voltage divider. In addition, there is another lamp that provides a nice green illumination for the flash 'computer' dial. This looks like a neon indicator lamp but with an internal phosphor coating. I have observed the spectrum of these things. I have seen two different gas fills in these that emit UV that makes the green-glowing phosphor do its stuff. One bulb type about the size of an NE-2H uses a mixture of neon and xenon. GE made those things (I don't know if anyone else ever did), which are called NE-2G lamps. The other type, a much smaller one that I found in Radio Shack's 272-708 green neon "cartridge", uses a mixture of neon and krypton. (Don Klipstein (don@misty.com or klipstei@netaxs.com)). The Vivitar schematic is split into two parts with FL1, C1, and L1 duplicated to improve readability. ----------------------------------------------------------------------------- @endnode @node 6.5.1 "Vivitar Auto 253 power supply" AC D3 +-< IN >-|>|--+ S1 | | DC AC | D1 |X D2 Flashlamp +--o o +-o o +----|>|----+--|>|--+----------+-------+-------------------+ | /..|.. / | | | | | FL1 | | | +| | | | LT1 | | | | | | ___ +---|------+ +++ ||C \ \ +| | | _ | | |o| ||C L1 / R5 / R3 _|_ | | ___ BT1 | | |o| ||C \ 1.2M \ 3.3M | | | | | _ 9V | | +++ ||C / / Trigger || | | | -| | C3 | | | | | || | | +---+ T1 +-+--||--+ | | | | C2 T2 +--|| | | ||(3 220 | \ R2 | | +--||--+ ||( || | +-------+ ||( pF | / 1,2M | Energy | | .047 | ||( || _ | | 2)||( 118 | \ | Storage | | uF +-+ ||( |_|_| | R1 <.1 )||( | | | 380 uF | Ready | )||( | / 4.7K )|| +---+ | | +| 350 V +++ | Shutter )||( | \ +--+ ||(5 | +----+ __|__ |o| IL1 |- )||( -| / | 4 ||( .2 | | _____ C1 |o| | S2 +-+ +-+ | | | +--------+ | | +++ | | | | | |/ C 1 | | | -| | +------+--+-----+ | +--| Q1 | | | | | | | | | |\ E 2SB324 | +_|_C4 | | | / R4 _|_ C5 | | | | ___ | | | \ 3.3M --- 100 pF | +----|-----------+ - | 10 | | | / | | | Invertor | uF |Y | | | | | +----------------+----+-------+----------+-------+---------+---------+ ----------------------------------------------------------------------------- @endnode @node 6.5.2 "Vivitar Auto 253 power supply operation" 1. DC 9 V: The invertor boosts the battery voltage to about 300 V. This is rectified by D1/D2 and charges the energy storage capacitor, C1, through the inductor, L1. OR 2. AC 220 V: The line input is rectified by D3 and D1 resulting in about 320 V peak which charges the energy storage capacitor, C1, through the inductor, L1. 3. The trigger capacitor, C2, charges through R3, R4, and T2. 4. The neon bulb, IL1, signals ready by glowing when the energy storage capacitor is nearly fully charged. 5. Pressing the shutter closes S2 which discharges C2 through T2 generating a high voltage pulse (4-5KV) which ionizes the xenon gas in the flashlamp, FL1. 6. The energy storage capacitor discharges through L1 and the flashlamp. ----------------------------------------------------------------------------- @endnode @node 6.5.3 "Vivitar Auto 253 exposure control circuit" | <--- Power Supply --->|<---------- Automatic exposure control -----------> | D2* Flashlamp Quenchtube R6 X >---|>|---+-------+---------+---------/\/\/\---------------------+-----+ | FL1* | | | | _|_ | | QT1 | | Main | | | ||C _|_ Quench | | Trigger || | ||C L1* | | | Trigger C6 _|_ | From T2 || | ||C | o || .047 uF ___ / ---|| | | | ||------------------+ T3 | \ R7 || | | | o || )|| | / 1.2M || _ | +_|_ |_|_| )|| C7 | \ |_|_| ___ C1* | )|| +----||---+ | | - | 380 uF | )||( .047 uF | | | | 350 V | )||( | | | | | )||( | | Y >---------+-------+---------+ +--+ +--+------|-----+ | | | | | | +----------+ | | / | | | | R10 \ __|__ SCR1 | | | 1K / 470K _\_/_ M21C | | / Flash Sensor \ LS1 R8 C9 / | 200 V | | \ R8 Power Opening | +----+----+-' | .8 A _|_ C8 | / 2.2M --------------- CDS | +++ | | | --- 100 | \ Low 1/8" Light | |/| / _|_ | | pF | | High 1/32" Sensor | |\| \ --- | | | | Man Closed --> | |/| / |.05 | | | | | +++ | | uF | | | | +---+ +----+----+----------+------+-----+ | | | | _|_ C10 __|__ | --- 100 _\_/_ D4 | | pF | | | | +--------+---------+ ----------------------------------------------------------------------------- @endnode @node 6.5.4 "Vivitar Auto 253 exposure control operation" The power inputs, X and Y, may come from the Vivitar Auto 253 power supply circuit (above), other battery/AC adapter powered invertor, or other AC line operated power supply. 1. Quench trigger capacitor, C7, charges from energy storage capacitor, C1, through voltage divider formed by R7 and R8. 2. Flashlamp is triggered by 4-5 KV pulse from main trigger transformer, T2 (not shown) when shutter contacts close. 3. Because of series inductor, L1, voltage across flashlamp drops abruptly when current starts flowing. (NOTE: I am calling this an inductor - from appearance only - as it is unmarked. It may just be a small high current resistor). 4. This negative step is coupled by C6 to cathode of the quench trigger thyristor, SCR1. The anode-to-cathode voltage does not change but the cathode becomes negative with respect to the energy storage capacitor negative (common) terminal which feeds the gate circuit. 5. CDS light sensor, LS1, R8, and C9 form an RC network with a time constant inversely proportional to the light reflected off of the subject. Voltage on SCR1's gate increases as C9 charges. 6. When enough light has been detected indicating proper exposure, SCR1 is triggered dumping C7 through quench trigger transformer. Resulting 4-5 KV pulse ionizes (xenon) gas in quenchtube. 7. The quenchtube has a lower voltage drop than the flashlamp and thus bypasses any charge remaining on C1 around FL1 terminating the light output. ----------------------------------------------------------------------------- @endnode @node 6.5.5 "Vivitar Auto 253 general notes" 1. Cycle time is independent of flash duration as energy storage capacitor is always discharged nearly fully by either flashlamp or quenchtube. 2. Components in automatic exposure circuit denoted with * are duplicated from power supply section to improve readability of schematic. 3. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.6 "High power (laser pump) strobe circuit" Here is a schematic for a high power xenon strobe unit suitable for pumping a small Ruby, YAG, or Neodymium-Glass laser rod. (The term 'small' is used here in a relative sort of way - well at least compared to those at the Laser Fusion Facility at the Lawrence Livermore National Laboratory.) Power D1 R5 L1 +-----+--|>|--/\/\--+-----+------------------CCCCCC----------------+ ||( | 5 KV 5K | | 25 uH (est) | ||( |.5 A 25 W +_|_ / | H --+ ||( | ___ C1 \ R1 C1-C4: Energy storage | )||( 600 | - | / capacitor bank, Flashlamp | 115 )||( VRMS | | | 3600 uF, 450 V (each!) FL1 | VAC )||( 200 | +-----+ +| 2A )||( mA | | | R1-R4: Voltage drop _|_ )||( | +_|_ / equalizing resistors, | | | N --+ ||( | ___ C2 \ R2 200K, 1 W Trigger || | ||( | - | / 30 KV || | ||( | | | R7 + C5 - +--|| | +-------------------+-----+--/\/\--+-------+-----||---+ ||( || | T1 | | | 1.8M | | 3.9 uF | ||( || _ | | +_|_ / 1 W | | 450 V | ||( |_|_| | ___ C3 \ R3 | | | ||( | | - | / \ | +-+ ||( -| | | | / R8 __|__ SCR1 )||( | | +-----+ \ 1M _\_/_ C107D )||( | | | | / / | 400 V )||( | | +_|_ / | | | 4 A )||( | | ___ C4 \ R4 | | | +-+ +-+ | | - | / | | | | T2 | | | D2 R6 | | | | | | | | +--|<|--/\/\--+-----+--------+-------+-----+----+--------+---+ 5 KV 5K R9 | R10 | .5 A 25 W Fire >--/\/\--+--/\/\--+ (+5) 100 100 ----------------------------------------------------------------------------- @endnode @node 6.6.1 "High power (laser pump) strobe operation" 1. Power transformer, T1, in conjunction with D1, D2, and C1-C4, provides 1.7 KV DC. The power supply doubler capacitors are also used as the energy storage capacitors. Resistors, R1-R4, equalize the voltage drops across the series capacitors to compensate for slight differences in leakage resistance. R5 and R6 limit inrush current and charge rate. 2. The trigger capacitor, C5, charges through T2 from the voltage divider formed by R7 and R8. 3. Ready light and capacitor bank voltage monitoring circuits are not shown. 4. Applying a 5 V signal to the Fire input turns on SCR1 dumping C5 into the primary of the trigger transformer, T2. This generates a 30 KV pulse which ionizes the xenon gas in the flashlamp, FL1. 5. The energy storage capacitor bank discharges through L1 and FL1. ----------------------------------------------------------------------------- @endnode @node 6.6.2 "High power (laser pump) strobe notes" 1. WARNING: If you thought line operated equipment was dangerous, this is much much worse. The power transformer output is enough to kill. Once doubled and stored in the capacitor bank, it is LETHAL. The total energy storage is about 1300 W-s (this is not a typo!). Based on one estimate, this is enough energy to KILL 20 adult humans simultaneously with the power supply unplugged from the AC line - and still have some juice left over. TAKE EXTREME CARE! 2. Fuse, power switch, power-on light, and all other absolutely essential safety interlocks and indicators are not shown. R1-R4 do act as bleeder resistors and will discharge the capacitor bank to safe levels in about 10 MINUTES. However, don't depend on these. Resistors can fail. Use the capacitor discharge tool and indicator. 3. The power transformer from a tube type (old) TV set would probably be suitable for T1. Microwave oven high voltage rectifiers may be used for D1 and D2. A high power xenon tube like this requires a 30+ KV trigger pulse. Those little tiny trigger transformers will NOT work. Capacitors, C1-C4, must be rated for photoflash rapid discharge. 4. High power strobes require special flashlamps - anything from a pocket camera or electronic flash will explode into a mass of molten bits of glass and metal. This design is derived from one using a tube from EG&G Electro-Optics. I do not know if they still exist. Even a properly specified flashlamp may explode - operate only behind protective shielding. Flashlamp cooling must be adequate for desired cycle time. 5. L1 helps to shape the discharge current pulse. For high power strobe designs, a series inductor is essential to optimize power output and prevent damage to the flashlamp due to excessively high current and negative voltage (undershoot resulting in reverse current). A damping factor of .8 is generally recommended. The 25 uH value is just an estimate - L1 must be calculated for each combination of energy storage capacitor value, voltage, and the impedance characteristics of the specific flashlamp to be used. 6. Flash energy is about 1300 W-s. For a typical flash duration of 250 uS, this is an equivalent power input to the flashlamp of 5.2 MW! Adjust component values for the desired application. 7. DO NOT even think about staring at the flashlamp when fired. The peak light output is equivalent to at least 500,000 - 100 W light bulbs! Even when averaged over the 1/40th of a second typical response of the human eye, this is still more than 5,000 - 100 W light bulbs. (NOTE: this estimate takes into account the increased luminous efficiency of xenon flashlamps compared to incandescent light bulbs.) 8. Make sure all optical components - especially the flashlamp - are cleaned with isopropyl alcohol and a lint free cloth to remove all traces of contaminants. 9. | | ---+--- are connected; ---|--- and ------- are NOT connected. | | ----------------------------------------------------------------------------- @endnode @node 6.7 "Simple commercial timing light" This schematic was taken from a cheap commercial automotive timing light. R1 150 ohms D2 1N4007 H >--------/\/\/---+-----|>|------+------------+ _ 10 W | | | FL1 _|_ | D1 1N4007 |+ +-|-+ N >---- ----+ +--|<|--+ _|_ 16 uF | | || HV Wire Power |+ | C2 ___ 420 V | ||--------< From #1 Sparkplug _|_ 16 uF | |- | _ || C1 ___ 420 V | | +-|-+ |- | | | Flashlamp +------------+------+------------+ ----------------------------------------------------------------------------- @endnode @node 6.7.1 "Timing light operation" 1. D1 and C1 form a half wave doubler which produces a waveform across D1 which is approximately a sinusoid with a p-p voltage of 2*1.414*VRMS of the line or about 320 V. (The peaks will get squashed with a significant load). 2. C2 charges from this through D2 to about 300 V. The flashlamp fires when triggered by the HV pulse from the #1 sparkplug connection. NOTE: this requires a direct connection, not an inductive pickup. 3. I would think that there will be some beating of the charging and flash for high rpms but the timing will be accurate. In other words, it will not fire for every rotation of the crankshaft since C2 cannot recover quickly enough but will flash at the proper instant when C2 has charged to a sufficient voltage. (This is probably by design - otherwise, the flashlamp would overheat very quickly at high rpms.) ----------------------------------------------------------------------------- @endnode @node 6.8 "Variable intensity variable frequency stroboscope" The circuit in the companion document of this name is designed to provide a variety of options in terms of repetition rate, flash intensity, and various repeat and triggering modes. Due to its complexity, it was drafted using OrCad SDT (Schematic Capture) and output in postscript format. The PostScript file is available compressed with PKZIP (for DOS/WIN/MAC users): o strobex.zip (9KB) and GZIP (for UNIX users): o strobex.ps.gz (9KB) The design includes: 1. Line operated voltage doubler power supply. 2. Power transformer operated low voltage logic supply. 3. Variable frequency repeat mode controlled by 555 timer. 4. Optoisolated external trigger input. 5. Selectable flash intensities of .2, 2, and 20 W-s. 6. Autorepeat speeds from .05 to 100 Hz (though obviously, the flashlamp will not operate at all intensities for these entire ranges.) Parts of this circuit have been built and tested but the entire unit is not complete. Maybe someday. ----------------------------------------------------------------------------- @endnode @node 7.1 "Why do roulette wheels sometimes appear to spin backward?" Roulette wheels and wagon wheels spinning backwards represents a form of aliasing due to sampling. OK, the technical jargon aside this effect will only take place in a situation where images are captured at discrete intervals as they are in a motion picture or video - or when illuminated with a repeating strobe. For motion pictures, something like 24 images per second are recorded; for video there are 30 images per second (in the US, 25 in many other countries. However, the use of interlacing where a complete frame is scanned in two parts - the even and the odd lines - complicates the explanation so I will restrict the remainder of this discussion to motion picture film). If the rotation rate of the wheel is such that one spoke or slot goes by a given position in exactly 1/24th of a second, the wheel will appear stationary since successive images will be identical. If it is moving a bit faster than this it will appear to be moving forward slowly. However, if it is going a bit slower, then it will be appear to be turning backwards slowly. The shorter the exposure with respect to the total frame time, the sharper will be the apparent effect. The number of slots per second of perceived motion will be equal to the difference in frame rate and number of slots per second passing a given point. So, a roulette wheel rotating such that 23 slots are passing by per second captured on a 24 frame per second camera will appear to be moving backwards at 1 slot per second. The same applies to the use of a strobe light to freeze repetitive motion like the rotation of a shaft. It is all a matter of the relative speed of the sampling (the movie, video or strobe) with respect to an object which is periodic like a roulette or wagon wheel. You can perform a simple experiment: run an electric fan under a fluorescent lamp (one with an ordinary magnetic ballest). The light from such a lamp is not continuous but pulses 120 times per second. Watch for stationary or slowly rotating blade patterns as the fan speeds up and slows down. See if you can compute the speed of the fan from this behavior. ----------------------------------------------------------------------------- @endnode @node 7.2 "Kevin attempts to abuse a strobe" (This from: Kevin 'Destroyer of Worlds' Horton (khorton@tech.iupui.edu)) Just for funsies, I decided to see how much torture I could inflict on the flashlamp and energy storage capacitor from one of those little Kodak cameras. The tube was 1.2" long, in a metalized plastic reflector, with a thin metal backing to hold it in. The capacitor was 120 uf, 330 V. I hooked it up to my inverter (12 V->300 V at high current) and fired 'er up! Pop, pop, pop, pop, pop, pop, pop, (turn up trigger oscillator frequency) popopopopopopopopopopopop! It was firing about 30 or 40 times a second; it appeared as it was constantly on! I turned it down to about 15 flashes a second, and let it run. First thing I noticed was that wonderful scent of melting acrylic. Then, I noticed that the tube was kind of skewed in the reflector. The plastic was in full smoke-mode by this point. Still, the tube kept firing! (Let's see: 5 W-s times 15 flashes per second is 75 W average power, not bad for an itty bitty tube --- sam). I left it on a bit more, and the plastic really started the smoke-signals! I noticed that one electrode was glowing cherry red. Even after all this torture, it kept going! The smoke was getting too much, so I hit the 'off' on my inverter. A few more gouts of smoke, and the little fire I created was extinguished. I let it cool down and then I examined the damage. The reflector was totaled; the tube had all but melted clean through. When I touched it, the little metal plate popped off. On closer examination, the tube appeared to be in good shape. I couldn't see any visible damage to either the electrodes, or the glass seals. A quick test reveals that the tube still functions. As a side note, the storage capacitor got quite hot; probably around 35 degrees C. All in all, an interesting test, I must say. The next will involve connecting up a normal NE2 neon bulb and observing the results of high voltage and high current on it. I suspect it will be quite spectacular, so I'm taking precautions - It will be performed in a proper enclosure, so if the neon decides to really go 'pop', it won't do any damage. ----------------------------------------------------------------------------- @endnode @node 7.3 "Parts suppliers" Common electronic components can be obtained from any large distributor. Even Radio Shack may have what you are looking for. However, many do not list any xenon flashlamps or trigger transformers. Mouser stocks a few xenon flashlamps and trigger transformers suitable for both small and medium power strobes. Dalbani stocks quite a large variety of xenon flashlamps of all sizes and styles. Dalbani Tel: 1-800-325-2264 (US) Fax: 1-305-594-6588 (US) Tel: 1-305-716-0947 (Int) Fax: 1-305-716-9719 (Int) Excellent Japanese semiconductor source, VCR parts, other consumer electronics, Xenon flash tubes, car stereo, CATV. Mouser Electronics Tel: 1-800-34-MOUSER (Sales/Service) Tel: 1-800-346-6873 (US) Tel: 1-800-992-9943 (US Catalog Subscription) General electronics parts including trigger transformers, magnet wire, rechargeable batteries, laserdiodes, photodiodes. ----------------------------------------------------------------------------- @endnode