Is there any way to control the voltage reference for the ADC in the spark core? I have some signal wander in positive and negative domains.
The reference voltage for the ADC is tied to a filtered version of 3.3V and is not changeable. The STM32 ARM does not allow negative voltages anyway.
You have two choices:
- You can add an op-amp or two to do signal scaling and center the range on 1.65V
- You could try AC coupling the input with clamping diodes.
Can you say more about the signal you are measuring? Fast? Slow? What voltage range?