digital gauge??

[hjl4]

Can this be done without a 100 resistors?
Imagine 100 phototransistors all lined up side by side forming a line, and let's say #73 is hit by laser beam, phototransistor allows current thru, and a microprocessor know's which one was turned on.
Is there a trick to multiplexing this stuff so a 16f877 can do this without 100 resistors???

 

[hjl4]

Ok I guess judging by the response time, that no one is there, or they don't know.
I figured it out myself, 32 x 32 = 1024. I can multiplex 1024 photo diodes together and get 1024 resolution. 32 rows 32 columns. 32 I/O pins on 16f877.
Yes totally possible.

Thanks anyways.

 

[jacob.zurasky]

32 rows by 32 columns would require 64 i/o lines, maybe look into running a few shift registers

 

[ericgibbs]

hi hjl,
Attached scan1.pdf.

The HEF4067 is a 16 Channel analog mux.

Connect the photodiodes across the RC matrix as shown.

Use the fall in resistance of the PD.

Scan the Cols one at a time, then scan thru all the Rows for that Col.

Test the ADC input for a Vsignal at the RC scan combination.

Let me know what you think.

Regards
EricG