Phototransistor applications?

[Byte_Butcher]

Use it in active mode with an emitter resister and feed a ADC. ?
What PIC are you using? does it have an ADC?

[nemesis]

I am glad someone asked, I was just starting to look in to how to do this same task.

I just picked up a few of these. I was wondering the same thing. I found a few circuits on the net. Here is a few:

http://www.uoguelph.ca/~antoon/circ/sensor2.htm
http://www.acroname.com/howto/photor...oresistor.html

Please post back if you come up with anything.

[mackrackit]

I just picked up a few of these. I was wondering the same thing. I found a few circuits on the net. Here is a few:

http://www.uoguelph.ca/~antoon/circ/sensor2.htm
http://www.acroname.com/howto/photor...oresistor.html

Please post back if you come up with anything.

Resistor?
Transistor?
Whats the difference?

[nemesis]

Yeah those links were for resistors, his question is about transistors. My mistake. Maybe the resistor photocell might be easier than active mode on the photo transistor. Maybe that can produce the same results with intensity... Seems a little easier.

-Nemesis

[RussMartin]

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.

[Acetronics2]

Hi, Russ

Could you tell us what you want to do ???

Phototransistors sensitivy range can be greatly stretched ... but the circuit used ( yes ...OPAs needed ) will depend upon the light variation frequency to be detected.

sooooo ... without knowing what to achieve ... tons of solutions !!!

Alain