Circuit design question, multiplexing 270 phototransistors


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    The DG408 is an 8 channel analog multiplexer. It needs 1 ADC pin and 3 control pins. It might be possible to use 8 of them, each with its own ADC pin, with their control lines in common but that still only gives you 64 channels so you would need 5 such setups (i.e. 5 PICs w/8ADC pins + 34 DG408s). That might still be better than using motorized rotary switches which get expensive and bulky. You could do it with 5 each PIC16F88 which only have 7 ADC pins. 5*7*8=280 total channelsYou can reduce the number of PICs to one by cascading the DG408s. This takes additional control lines and is a bit harder to visualize but (if my math is correct) you can have 448 channels with one PIC12F88 and 9 DG408s, needing 6 control lines.

    What type of output is needed?
    Last edited by dhouston; - 17th September 2009 at 16:47.

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