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Originally Posted by foobert
fowlerm, what say you scope the output of the controller and take a picture for us. might be worth a thousand or so words. maybe even more to my addled old brain.
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When I said I'm going to scope the control lines on the mux, what I'm going to do is take an oscilloscope (scope) and watch the different control lines on the multiplexer (mux). In the picture that I attached, the small 16 pin chip near the top right of the green pcb is a Rohm BU4051BCF 8 channel analog multiplexer/de-multiplexer. There are 3 control lines (A, B, C) that are used to select channel that will be output from the multiplexer. For example, if A-C are low, the output channel is channel 0, if A is high and B-C are low the output channel is 1. Think of A-C as 3 bits in a number, with A as the least significant. The maximum value of a three bit number is decimal 7. The multiplexer's channels are 0-7, so the decimal value of this three bit number is the channel that is selected for output.
Also, there is a high-res picture
here if you want higher detail. It's 1.8 megs, so dial-up users have been warned.