InfraRed Data Com

[languer]

You really need to understand what you are trying to achieve and the components required.

This link provides good basic information on IR communications. If you do not have to use the PHOTO diode, a better choice is an IR receiver (e.g. PNA4602M, TSOP1240, etc). These have the PHOTO diode and required conditioning circuit built-in.

If you must use the PHOTO diode, first of good luck. Second look at an IR receiver to get an idea of what is it you need to add to the PIN diode itself.

An example diagram is attached.

[rayzrocket]

Thanks,
I only need a range of three feet. But its going underneath a car, where it will get much ambient solar background; as well as any IR coming off hot objects.
The IRda recievers commercially available are made for OOK on some operating frequency such as 38khz.

I am currently building a AGC with a variable value comparator using the PIC's built in comparator with Vcref value control.

Thanks for your inputs.

Once I get things working, I'll post my design.

-ray

[Melanie]

I can get a very low level (25mv) square shaped signal from the photodiode using a 15k resistor instead of a 120k. Problem is the NOISE!! There is about 10mv of noise, so my SNR is horrible at this point.

On another thread I described how you can get your Comparator to amplify your signal and filter noise. Looks like you're already thinking down that route. Simply squirt your Data & Noise into a Comparator and software set VRef a millivolt or two above the noise. Suddenly you're left with clean 0-5v swinging data and no noise. You can be even more clever, by sampling the average noise level using an ADC, you can then calculate WHERE to set VRef on the Comparator. That way you can automatically track the noise, ensuring the Comparator always extracts good data regardless of conditions. Your Data only needs to be a couple of mV above the noise to extract it.