For differential voltage measurements I have been using an add on ADS1115 I2C 16bit ADC module.? Can be programmed for either 4 single ended or 2 differential inputs.? Higher resolution and? input resistance than just the Arduino alone.??With just the Arduino I usually had to add a buffer op-amp to get the input resistance up to what I needed.? It also has a programmable gain amplifier that makes it very sensitive,? I have used it to measure voltage drop across long circuit board traces.?
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DuWayne,? KV4QB
DuWayne Schmidlkofer