Quote Originally Posted by Byte_Butcher View Post
Use it in active mode with an emitter resister and feed a ADC. ?
What PIC are you using? does it have an ADC?
For that group of trials I was using the 12F683 which, yes, does have ADCs.

The problem, as I wrote before, is the range of the phototransistor response. Assuming an emitter resistor of 1 megohm and a current of 1 microamp, this puts 1 volt on the resistor. (The dark current is in the nanoamp range.) Given a 5 volt supply, 5 microamps (not very much light!) is about as far as you can go.

The smallest "slice", assuming 8-bit conversion, is 19.6 millivolts. Since the phototransistors I was working with can provide current ranging from a microamp to 5 or more milliamps (essentially 5 orders of magnitude), obviously something has to give--either the low end or the high end.