Circuit design question, multiplexing 270 phototransistors

[dhouston]

Reducing it to a single ADC pin would only require one more DG408 and three more control lines but it does complicate the switching logic, going from 6-bits (with 7 ADC pins) to 9-bits.

40 DG408s + 1 PIC with 1 ADC pin and 9 control pins.

However, there is only one ADC channel with a PIC - it's input is merely being switched internally so there''s no real difference between using all seven ADC pins on a PIC16F88 and using only 1 ADC and adding another DG408.

[falingtrea]

If the OP could live with digital outputs for the photo transistor levels, then you could just use I/O expanders. Comparitors would be cheaper than analog switches. Some I/O expanders can read 26 I/O pins with one package.