Bdoop21 said:
Thanks Torben,
I think if I have a phototransistor on one side and a photodiode on the other that might do it. BUT I have used Infared phototranisistors for a pulse detector. I think it is basically the same principal, right?
Basically, depending on what your pulse detector was detecting pulses of. But a phototransistor and photodiode both do essentially the same thing: detect light. So a detector on each side probably isn't what you're looking for. A photodiode and an LED are not the same thing: an LED gives off light, while a photodiode detects it. The picky will note that an LED can in fact be used to detect light.
The only thing about using an infared sensor is that it seems SO sensitive. It seems to be affected by ambient light more than (i think) a red laser light would be. Is that right?
Well, the laser will work somewhat better in general simply because when it's shining on the detector, it is delivering a whole lot of light, so the difference between it being on and off is much greater and therefore is easier to detect. However, ambient light is always going to be an issue unless you can somehow bury the detector. For instance, in my foosball scorer, the detector is about an inch deep inside a black plastic void, which is itself inside the black goal cup--not much ambient light gets in there, so I never have problems with ambient light shining on the detector. But if you can't do that, then AFAIK you pretty much *have* to modulate the light beam you're sending from the one side and have the detector side only trigger when it can no longer sense a beam of that frequency shining on it. Otherwise when your beam is blocked, the detector could easily still receive enough environmental light to make it think the beam had never been blocked.
I think I would prefer if I could actually see the laser light and only if and when that very specific laser was interrupted my fan would turn on.
Yep, that's the idea. If you are better with the physical stuff than the electronic, and if your design allows for it, you could maybe get away with burying the detector. I mean make it really hard for ambient light to get to it. Maybe take a Bic pen, remove the ink tube and end cap, coat the pen inside and out with matte black paint, and shove the phototransistor in the narrow end with the leads sticking out. You'll also need to block light from hitting the back side of the detector where the leads come out, since that can be enough to register. The laser is then aimed so it shines in the other end, so that it has to be aimed carefully so it shines down the whole length of the pen before striking the phototransistor. The matte paint inside should help keep ambient light from bouncing down the tube onto the detector, depending on how bright the area is where you'll have the setup.
I said a thin piece of paper, because I want it to be pretty sensitive, but not so sensitive that a cat would blow the paper as it walked by. I'm sure a thick piece of paper would be good enough for my needs, actually maybe even better.
So what exactly are you trying to do? Have a piece of paper fall into the beam, which turns on the fan, which blows the paper up, which turns the fan back off and lets the paper fall again?
I will fill in my profile, I have just been so excited reading all the posts and asking questions that I havent gotten to that part. But, I am in Seattle Washington and have ordered plenty from Digikey and Mouser in a very short amount of time. I am VERY new to electronic work and dont really know anything...
So thank you for anything and everything you all have to offer.
-MBE
Hope this is at least giving you some ideas. I'm posting this now but I'll try to dig up some references on the modulation in case that's needed. (You might have guessed that I'm a hobbyist and not an EE or anything. I'm learning too but I have a few projects under my belt.)
Torben