ir detection circuit

[kailas]

Hey everyone, I'm new to electronics and need some help. I know the basic understandings of circuits but don't quite understand microcontrollers. I'm trying to construct a board which can identify infrared light being detected by 56 different ir detector. I'll be OK with the programing when i have constructed the board but need help making it. My question is, how many ir detectors can fit onto a standard 28 bin microcontroller (such as the one in the $50 robot tutorial, ATmega8 AVR), and is there a microcontroller which can handle all of the ir detectors or will i have to link up several microcontrollers?

[Razor Concepts]

Look into multiplexer chips, they allow you to monitor a bunch of inputs with only a few pins.

[kailas]

Dude you legend! Thank you very much! Don't suppose you know a cheap place to get them? Only place i can find is hong kong :/

[Soeren]

Hi,

If you tell a bit more about your application, perhaps a simpler solution could be found.
Like, perhaps what you need to do, could be done with less detectors, or perhaps it would be allright to parallel them (if they're open collector types). Perhaps there's a solution that you just haven't thought of - 56 detectors sound quite exxagerated.

The more you tell, the better help you'll get.

[kailas]

Ahh good point. Well I'm trying to make a multitouch screen for my computer screen. It's going to be make 2 rows of ir lights going from the x and y axis on one side and then ir detectors on the other x and y axis. I know it will work just need to figure out the circuit. What do you think?

[chelmi]

What kind of emitter are you going to use? I'm afraid the beam will be too wide and you will light more than one sensor with a beam and won't be able to detect interruptions...

[kailas]

I was thinking of just a plain simple led light, and i was thinking to surround each emitter by a box so to speak , so that it can only emit straight or close enough to straight and then having the detector in the same kind of layout. What do you think?

Pic of my idea, sorry it's a bit messy <a href="http://tinypic.com" target="_blank"><img src="http://i26.tinypic.com/4lrjiu.jpg" border="0" alt="Image and video hosting by TinyPic">[/url]

any ideas of how i can make this easily?

[Soeren]

Hi,

For the emitters, one cheap LASER-pointer and one tiny mirror could be used, with some thin polycarbonate (or acrylic) plastic in small slices used as transparent mirrors.
That way you'd have exact control over where the beams hit - and save all the LEDs

Whatever method, always place the horizontal row of emitters at the bottom. That way the receivers won't see as much of the ambient light.


Did you consider buying one of the loose IR-frames to mount on a monitor for the very same purpose? (They were all the rage back in time).

And there are several other ways of getting touch on a screen, but if it hasn't got at least half the resolution of the monitor (so that you can draw directly on the screen, I fear that you'll get very bored with it. Either use a keyboard, a mouse or touch - don't make yourself a situation where your hands have to scoot all over the place all the time.

[kailas]

ok, very good point. Maybe I should leave making the multitouch for now and just buy a touch monitor when one comes out cheap. lol thank for the advice though everyone
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