Arduino Motor Shield AO signal question.

Using Arduino Motors, Mechanics, Power and CNC
#1

I have an Arduino Motor Shield and I have an issue with the A0 pin.
I am reading a small amount of voltage at that pin. Even when the motor output is at 0.
I am also able to read a small amount of voltage there using analogRead. Even though the motor output voltage is 0.

voltage reading of between .099 and .104 volts. at 0 output to motor.

The change in voltage however is approximately equal to the current delivered to the motor I am running. I am dealing with a very low current motor, 60ma at max draw so my voltage change is small. I can measure the current to the motor on the output of the Motor Shield, do the calculation of voltage change on the A0 pin and those values are within a couple of ma. So the readings appear to be accurate.

Is there a possible issue with my Motor Shield, because I may have messed up that output while attempting another sketch not fully understanding that the A0 was dedicated to current sensing on the Motor Shield.

#2

I just purchased mine a few days ago - and I'm seeing a similar thing on mine. A0 reads About a 0.1 volt reading at a 0 setting for analogWrite(). Oscilloscope shows about the same voltage on A0 as well.

#3

Out of curiosity, I looked at the circuit diagram.
The output of the current sense resistor passes to an op-amp before going to A0.
A small DC offset may be difficult to avoid. Simply allow for it in your code.
If you want accurate results you should calibrate anyway.

Joe

#4