When I run the example sketch "01.Basics" -> "AnalogReadSerial" on the Arduino Uno (without shield). I get a nice, almost linear sweep from 0 to 1023.
When I do the same when the Uno is combined with a motor shield, I get a heavily skewed sweep from 11 to 750. With skewed I mean that the first 95% of the rotation makes the value sweep from 11 to 30 and the last 5% makes the value go from from 30 to 750. When I leave the potentiometer all the way up, the value slowly makes its way to about 790. Faster at first and then slower, like when you load a R-C cicuit.
There's a bipolar stepper attached to the motor shield, but it's not instantiated nor triggered in the code, since I'm using the example code for printing analogRead() to the serial monitor.
I get the same results when fed from just USB as well as from external power supply. Since I'm not driving any load, I thought it was OK to test without the external PS.
Attached is a picture of my setup.
Could my motor shield be broken?
Best regards, Marv