I do some digital photography. Recently, I've dug up some old photographic flashes. I'd like to try some sort of high-speed photography using the flashes, which provide a brief (< 3 ms) but intense flash of light. In order to get the shot to happen at the right moment, this will require some precise timing. The flashes will flash faster than the camera's shutter can operate, so the timing will be synchronized to the flashes, and the camera's shutter will be opened well before. The TI-83+SE and TI-84+/SE have a precise crystal timer, and two I/O lines I can use, and I have the assembly skills to make use of these. One can read from a trigger circuit, and one can trigger the flash(es).

The first point I wish to consider is the flash trigger. The flashes can be triggered manually via a simple two-wire interface. Between the two lines is a non-standardized voltage, and shorting the lines together triggers the flash. (Sound like some hardware you're already familiar with?) The flash will not trigger again until the voltage exists again for a short period. My camera officially tolerates up to 250 VDC between the two lines; the flashes I have put out between 25 and 50 V. If the flashes were putting out < 5 V, it would be pretty obvious how to connect a flash and calculator; however, as is, I need to shield the calculator from the high voltage of the flash. (Unless you think I don't.)

The second point is the trigger circuit. This far more open ended. I was thinking of a light-based system, where an object passes through a beam of light, interrupting the light shining on a photodiode. I'm a lot more willing to experiment on my own here, since there's less danger of the unit getting fried.

I'm interested in the results. In the past I've always read about microphone triggers with delay's introduced in the circuit to get the precise timing.

I'm also interested in how you go about getting this to work!

I agree that the calculator needs to be isolated from the 25-250VDC, s you have a whole bunch of options. You can use a low-voltage signal from the I/O port to turn on a power transistor (Which still requires the two devices to share a ground, or you can use a relay (which has a close-to-consistent delay due to the mechanical movement of the relay arm over to the solenoid). This also seems to be a place where an SCR or a TRIAC might be useful, but I'm ashamed to say I've never personally used one of those components.

I've used relays before. They're fun, if slow by digital standards.

Indeed, and since they're a relatively simple option, I'm thinking that they might work for DrDnar, since he could just compensate for their fairly consistent lag by, for example, moving his trip IR detector/emitter pair slightly further back along the path of the object triggering the photograph.

The trouble with a relay that I see is there's typically relatively high draw to actuate the switch. My thought would be a power FET such as a VN750, which also has the bonus of shutting itself off if something goes very wrong.

How would I wire up the transistor? Oh, and preferably, this will use parts from the local Radio Shack.

I don't know if I'd be crazy about that. Going off what Tari said, maybe the best would be to trigger a relay with a transistor; since the relay only needs to be on momentarily, a simple switching transistor won't have to dissipate that much heat over time.