How would I go about measuring an analog signal that has both positive and negative voltages on an arduino analog pin at a high sampling rate?

Question

I have a signal that fluctuates between -70mV and 50mV. How would I get the arduino mega to read this on an analog pin at a high sampling rate? Ultimately I am trying to graph the data in real time so it looks like this.

I have looked at the question posted earlier on EESE about reading positive/negative voltages and it gives info on a slow moving signal that ranged from -55V to 55V. I doubt this solution would apply to my situation though (attenuating signal with two resistors and then offsetting the range by using an op-amp summing circuit).

Answer 1

1. Using standard Arduino libraries, you will have trouble sampling above about 10000 samples per second.

2. If you manage to sample fast enough, you will need a place to put the captured data. Memory is notoriously scarce on Arduinos, and the other built in option is the serial port to dump it to a PC. You could also try to write it to an SD card. Don't know what the libraries are like for that, or if there's a readily available SD card adapter for Arduinos.

3. The Arduinos have a 10 bit analog to digital converter. Assuming a 5V reference, you are talking about 5mV steps. For the range you describe (120mV) you would only be using 24 out of 1023 steps from the ADC. You need an amplifier that multiplies by about 30, and that adds 2.5 V to the result.

If "less than 10kHz" fits your definition of "high sampling rate" and you can build a small circuit board for the amplifier, then you might be able to do something useful.