question for you all that have more experience than I... so most of you...

will an IR sensor pick up indirect IR light, for example rather than having a IR LED pointed directly at an IR sensor, if the IR LED was pointed at a surface and the IR sensor pointed at the same surface, will the IR sensor pick up the IR light on the surface... if that doesn't make sense then perhaps this will.. an IR LED and an IR Sensor both pointed at a wall directly in front of them. will the sensor pick up the IR light that is on the wall.

also does a IR Sensor work the same way as a LDR? (change resistance depending on light) or is it an on/off situation.

 

Which IR sensor are you talking about? They are made in different ways:
1) IR receiver IC. They are used in home entertainment equipment.
2) IR photo-diode that needs an amplifier. There are two different circuits.
3) IR photo-transistor that has gain but is slow.
4) LDR that is a variable resistor and is extremely slow.

There is a huge difference between something that reflects well like a mirror to something that reflects poorly like black cloth.

 

The IR photodiode/LED method is definitely possible (I just designed one myself for a small robot) but it can be a little tricky and require some tweaking. The result is a pretty fast sensor, though. You can look into Sharp sensors (GP2D12, etc.) for a commercial solution that is a little slow (uses CCD). I'd be happy to provide some more details about my experience with the photodiode/LED method if you'd like, but there are probably plenty of people around here who know this stuff better )

 

thanks guys, I should probably explain a bit better this little idea I had, it's more of a novel thing and nothing would happen on it until I have finished all my other projects...

Which IR sensor are you talking about?

I didn't know, that's why I asked the question
how slow is slow? for the LDR, I would want something that would pick up a variable ammount of light.

imagine an array of white LED's, as you wave your hand over it, the led's directly under your hand (in the same shape) turn on. to varying brightnesses depending on the distance etc of the object. in photographic terms it would look like a "Negative" of whatever you pass over it.

the more info the better, this could potentially become a huge project so the more info the better.

 

Maybe something like this clever compound eye design would serve your purpose.

hgmjr

 

Look into TAOS (Texas Advanced Optical Systems) for their light to voltage converters. They are cheap, fast, and respond from IR to UV. Mouser carries them.

 

about ir led-photodiode sensor

 

With many LEDs above your hand then the resulting shadow is extremely fuzzy. Use a single very small LED then the shadow is distinct and very clear.

 

I forgot.
People have made LEDs sense light then make light in the same pattern as the sensed light.