Grounding the red wire causes the menu for calibration to appear. If the red wire is attached to a pin on the Nano,
that means that pin is always at zero volts. But that is what the program expects to start the calibration
routine. Without the wire "grounded", the pin should be high, or at 5v. It is likely that something happened to the
programming which caused this internally -- but there could be a physical reason for the zero volts. Look for that first.
john
AD5YE
