I have an arduino with two analogue inputs in use - 1 and 5 Bot inputs have AC signals, offset around 2.5v
The first is fed from the output of a MCP6S28 programmable gain amp - again with a low output impedance The second is fed from a MC33202 unity gain buffer, to provide a low output impedance input to the Arduino ADC
In my main loop, I sample both inputs consecutively(5 then 1), do some processing, wait 500mS, and repeat.
I have noticed that when the amplitude on input 1 increases, the voltage read on input 5 drops noticeably. However, using a 'scope the input to ADC 5 stays steady as a rock at all times, as does the powe supply rail to the arduino.
Can anyone suggest what might be going on? The signals are both at 50Hz, and I want to sample both inputs as close to concurrently as possible - so ideally don't want to add delays between the two reads.