What PIC to use with lots of photodiodes?

[PapaSnuff]

I will have a matrix of around 80 photodiodes, sensitive to IR light only, each with a very narrow beam angle (around 8 degrees). What type of PIC microcontroller would you recommend to poll the amount of IR light hitting each photodiode?

 

[Sceadwian]

Depends on how much voltage the diode puts out when it's exposed to light, I'm not so sure a photo diode can be used in a voltage mode on a PIC input without amplification. If reverse biased the photo diode will act like a varactor, but again the timing precision of the PIC may or may not be good enough for your diode and doing PWM and precise timeing on 80 pins would be likley not practical, most people have trouble measuring capacitance on one pin let alone 80. I think your best bet would be any PIC (or AVR my preference) with the photo diodes connected to a simple transistor as an amplifier for the PICs I/O lines. This is one of the reasons photo transistors exist, the photodiode is coupled to a transistor in a single unit. You need to explain the precision and refresh rate you need as well as they will greatly influence the circuit you'll build.

 

[PapaSnuff]

I would need a refresh rate of around 16 to 33ms. That would be a full refresh, where I had the individual voltage readings from all 80 phototransistors back.

I was thinking about using these:

Digi-Key - QSC112-ND (Fairchild Optoelectronics Group - QSC112)

(Also I can't tell the difference between the QSC112, 113, and 114)

 

[ericgibbs]

I will have a matrix of around 80 photodiodes, sensitive to IR light only, each with a very narrow beam angle (around 8 degrees). What type of PIC microcontroller would you recommend to poll the amount of IR light hitting each photodiode?

hi,
You could use a HEF4067 16 channel analog multiplexer.
For 80 PD inputs you would require 5 off, 4067.

The PIC would scan/select the 4067's and the output of the selected PD
via the 4067 would connect to an analog input of the PIC.

If required an OPA could be used amplify the signal before it drives the PIC analog input.
Most medium range PIC's have 5 analog inputs or you could combine all
5, 4067 inputs by using another mux driving one OPA and just one analog input.