So you have 50,000 wires from 50,000 resistors that you want to measure?
You may not be the first person to have to measure many sensors but you may be to first to need to do it for 50,000.
Are all the resistors approximately the same value?
The most straight-forward method is to use a multiplexer to sample each resistor.
For common 16-channel multiplexer chips (such as the CD4067) that would require some 3125 chips.
To address each channel would require 12-bits decoded into 3125 select lines and a 4-bit common address for each mux.
So all you have to do then is interface 50,000 resistor connections to 3125 multiplexers and generate the decode multiplexer logic.
Piece of cake.
The Digikey price for the CD4067 in 2000-up quantities is $0.532/ea so the total cost for the multiplexers alone would be $1663.
And allowing a half-square inch for each mux would require a board of 40 inches on a side for the multiplexers alone.
Thus your total system cost is more like a few thousand dollars as opposed to your budget of a few hundred.
And now you know why I decided to post this query here
I considered using multiplexers and the calculations ran off the page soon. I was genuinely hoping someone whould have done something like this at some point in history. Maybe having to keep track of all the RFID tags in a shopping mall or something. I also looked into Data Acquisition Modules but none come even close to the requirements I am looking to design even if I pay an arm and a leg.
Ok, heres another question. What if I scale it down to lets say 500 resistors. Are there any cheap microcontroller boards with enough input pins that I can use to develop this idea into a commercial product? I understand an arduino has multiplexer shields available but I am not sure one can develop something based on an arduino UNO for an industrial application.
Hypothetically, how would you approach designing a system to measure 500 (or even 250 if that helps) resistors sequentially, log that data and then transmit it to a main server every 15 minutes?