Best design to collect realtime data from large sensor array?

[Tom07]

Hello electro-tech Forums!

I am currently working on a multitouch project that requires me to read the data of lots of optical sensors (photodiodes) in realtime.
Since I am still relatively new to the electronics world, I was hoping some of the experienced members here could help me and point me in the right direction what approach / design might be best for my requirements.

In a nutshell I would ideally like to have:
- realtime data (at least 50Hz)
- maximum possible number of photodiodes per microcontroller (respecting the above)
- cost efficient

I'd be very thankful for some advice on what combination of photodiodes, ADCs, multiplexers?/FETs?/BBDs?, ...? would fit my requirements best.

Thank you very much in advance and have a great weekend!
Tom

 

[Mr RB]

Given that (if I understand you right) there will be multiple photodiodes activated at once, and photodiode output is binary (only ON or OFF) then I would;

1. group them in banks of 8 photodiodes
2. use a parallel latch to "grab" each group of 8 photodiodes
3. those 8 signals are now output on the 8 output pins from the parallel latch
4. then read those 8 pins into your microcontroller in one read

It would require parallel latch ICs that have tri-state outputs, but fortunately these are common and cheap. And obviously one latch IC for every 8 photodiodes.

It should be reasonably quick as it will only take a number of microseconds to set the latch and read 8 photodiodes.