Nuts & Volts - February 2006

Build a High Speed Photo Flash Trigger

Try adjusting the pot to other settings, and then clap at different distances. You’ll get a feel on the required sensitivity. Now connect and power-up the flash, and after its “ready” light comes on, repeat the experiment. The flash should trigger with the clapping, which means now you are set to go.

Remember that this is a combination electronic/photographic project. Once the electronic portion of the project is up and running, you must prepare your photography setup. Besides this completed project, you’ll require the following:

auto focus, then the shutter lag becomes an eternity. Therefore, you must manually set the camera’s focus.

Again, it goes without saying, that when attempting any photo setup which you have previously not done, a few trial pictures are required

beforehand to fine tune it. You’ll have to adjust focusing, exposure settings, composition, flash level, etc. This is a photography project after all and one that benefits enormously from digital cameras and their instantaneous feedback. NV

1. An external, non-dedicated flash. Dedicated flash units, designed to work specifically with particular camera models, derive syncing, exposure, and sometimes power from signals coming the camera itself.

2. A camera that allows full manual control. It could be either film or digital, SLR or fixed lens, but the important characteristic is that both manual focus and manual exposure control is required.

3. A tripod or something sturdy to keep your camera steady while your hands are busy with other things.

To actually capture the event, your camera setup has to be in an area of very dim lighting. Complete darkness is best. The reason being that you must open the shutter, initiate the event (pinching the balloon, dropping the bottle, etc.) which will create the noise that will trigger the flash itself, then close the shutter immediately after. The reason that the shutter must be open prior to the event to be captured is that all cameras suffer from shutter lag, which is the time from when the camera is triggered to take a picture, to the actual image capture. Digital cameras are especially at fault in this respect, but even a good film camera may have a delay — however minimal. This delay can be excessively long if the event one is attempting to capture is measured in fractions of milliseconds. It becomes even worse if the camera attempts to

PARTS LIST

(All parts available from Mouser Electronics; www.mouser.com / 800-346-6873.)

RESISTORS ❑ R1 — 4.3K, 5% 0805 SMT ❑ R2 — 4.7K, 5% 0805 SMT ❑ R3 — 2K 5% 0805 SMT ❑ R4 — 10K, 1% 0805 SMT ❑ R5 — 10K, 1% 0805 SMT ❑ R6 — 360, 5% 0805 SMT ❑ R7 — 10K, 1% 0805 SMT ❑ R8 — 100K, 5% 0805 SMT ❑ R9 — 100K, 5% 0805 SMT ❑ R10 — 1M, 5% 0805 SMT ❑ R11 — 3K, 5% 1/4W ❑ R12 — 360, 5% 0805 SMT ❑ R13 — 10K, 1% 0805 SMT ❑ R14 — 10K, 1% 0805 SMT ❑ P1 — 16mm linear taper potentiometer 100K w/ switch

PART NO. 260-4.3K 260-4.7K 260-2K 292-10K-RC 292-10K-RC 260-360 292-10K-RC 260-100K 260-100K 260-1M 660-CF1/4L3K 260-360 292-10K-RC 292-10K-RC 311-1700-100K

CAPACITORS (all 10% tolerance) ❑ C1 — 1μF, 50V (seetext) ❑ C2 — 0.1 μF X7R ceramic 0805 ❑ C3 — 10 μF, 16v electrolytic ❑ C4 — 0.1 μF X7R ceramic 0805 ❑ C5 — 1μF, 50V (seetext) ❑ C6 — 1μF, 50V (seetext) ❑ C7 — 10 μF, 16V electrolytic

581-SR225C104KAA 581-08055C104K 647-UVR1C100MDD 581-08055C104K 581-SR225C104KAA 581-SR225C104KAA 647-UVR1C100MDD

SEMICONDUCTORS

❑ M1 — 4. 7 volt electret microphone ❑ U1 — CD4538 dual CMOS monostable SMT ❑ U2 — LM358 dual general-purpose op-amp SMT ❑ U3 — LM393 dual comparator SMT ❑ D1 — Miniature red LED ❑ Q1 — 2N7002 N-channel MOSFET

252-EM9745P- 40 512-CD4538BCM 512-LM358AMX 512-LM393MX 606-430H1 689-2N7002

MISCELLANEOUS
❑ Potentiometer thumbwheel knob
❑ Nine-volt battery clips
❑ Perfboard or dedicated PCB

450-0009 121-0424/I

Photography — Besides the camera with the requirements outlined above, you’ll also require a camera tripod and an external flash. If the flash does not have an external trigger input, you will require purchasing a hot-shoe adaptor, as pictured in Figure 6. You may already own or have access to these. If not, B&H Photo and Video ( www.bhphotovideo.com / 800-309-4374) is an excellent source of photographic equipment and accessories.