The XMEN Clan Forums

*update* Got it working!!! Time to play!

Ok, I'm building a photogate/timer circuit to trigger a flash and I think I may have a faulty phototransistor. If I understand correctly, when my IR beam is broken (object between IR emitter & phototransistor) the voltage across the phototransistor should rise... correct?

I built a simple circuit w/ power supply, resistor, & phototransistor and then checked voltage as I (un)covered the phototrans from my desklamp light and there was no voltage change (9.00V... unchanged to 2 decimal places). I'd assume that your average desk lamp emits IR as well as visible light.


P.S. My timer circuit works beautifully. Just turning a pot adjusts delay from nearly instantaneous all the way up to about 0.5s. I suppose I could calculate the delay by measuring resistance across the pot... but trial & error seems to be working fine so far.


If/when I get this working... expect some cool pictures.

I'm assuming this is no longer relevant since you posted the OJ pic? Sorry I don't know the answer to your question but could probably find out.

Yep, I guess I could have deleted it... but I figured out that the phototransistor was fried & replaced it w/ a new one & like magic it worked!

If I had seen this earlier, I could have helped. Looks like you've got it.

You may want to put a very small resistor on the base of your phototransistor, just to put an upper limit on the current going through it.

And yes, your desklamp puts out IR. It's not very clean, but it's IR.