# multiplexing solution for high number of inputs in a grid pattern?

So, I'm working on a project right now to implement a large electrode sensor array for measuring bio-potential (128 x 128 sensors) that are in close proximity to each other (~0.06cm along horizontal and vertical). The signals themselves are relatively small, being on the order of tens to hundreds of micro Volts.

I want to select an arbitrary 64 sensor subset of these signals and route them to an amplifier circuit and then to an ADC circuit sampled at 250Hz (each selected signal has its own respective amplifier/adc path. Thus 64 amps and 64 ADCs, one of each for each selected signal). The configuration of selected signals only changes once every half minute or so, thus switching speed is not of paramount importance.

That said, I'm not sure how to go about selecting the signals to use properly. It doesn't seem practical to directly select 1 signal from over ~16,000 possible sources by having an enormous number of inputs to a multiplexer(s). I imagine (and vaguely remember reading some approaches like this) I could leverage the grid pattern to select from the analog inputs without massive amounts of logic, but I'm not entirely sure how I could go about doing that.

I would supply some datasheets to help out, but I'm still looking at this from a very top-down angle in order to get it conceptually straight in my head before hammering out specific components and such.

• You'll need to supply a lot more information. What are the sensors? Links to datasheets? What voltage? What response time to multiplexing power, for example? Commented Sep 9, 2017 at 22:18
• Do your sensors have an output enable feature? Commented Sep 9, 2017 at 22:30
• "Arbitrary subset" is awfully vague, too. Do mean an 8x8 tile of adjacent sensors, or something else? Commented Sep 9, 2017 at 22:38
• @DaveTweed Not necessarily 8x8. By "arbitrary" I mean that they could be anywhere in the grid without pattern. Vladimir Cravero: No they do not, but that's because I'm trying to devise the sensor select scheme on my own. Maybe that's a possible solution though? I'll try and add a bit more detail to the question, I'm amending it now. Commented Sep 9, 2017 at 22:44
• You are still not telling us what the sensors are and this matters. If they are two-wire such as RTDs it might be easy. If they are three wire (V+, GND and output) then it becomes rather different. "V" or "volt" as per SI units. Units name after a person are capitalised in abbreviated form but lowercase when spelled out. Commented Sep 9, 2017 at 23:52