Arduino Pro Micro digital input problem

I recently switched from Arduino Uno to a Sparkfun Arduino Pro Micro due to the size. The attached code works fine on an Uno with 2 foot switches attached without using any pull-up resistors. When I try this code on a Pro Mico it will only work with one foot switch attached. It doesn’t matter which foot switch or which pin I attach to. As soon as I connect the second foot switch even without pressing it the voltage of higher number goes low. I tried adding 2200 ohm resistors to VCC to overcome the problem assuming that the internal INPUT_PULLUP was not working but that did not change anything. I was originally using pins 2 and 3 but move to 3 and 4 to see if that made any difference and it did not.

Does anyone have any experience working with this board? Are there any substantial differences that change the way input works on the Pro Micro?

Any thoughts or suggestions would be greatly appreciated.

Bruce

IceboxArduinoIo_USB_INT.cc (2.7 KB)

I forgot to mention in the previous post that it is the 5V 16Mhz version of the board.

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Drew: Thanks for the reply. Yes I checked and rechecked the wiring. I tried another board still no help. The foot switch is connected through a 4 to 6 ft audio cable (depending on which one I use) with an XLR connector. It almost acts like it is staying in a high impedance mode and the wire to the foot switch is a antenna but it only causes problems when the second foot switch is added and as previously stated it dosen't matter which foot switch or which pin on the Arduino I attach to

Bruce