Issues with Arduino Zero Digital Inputs

[tyguy2]

Hello all,

I've embedded a SAMD21G (Basis for the Arduino Zero) into a PCB I've been designing. I've been using pins PA19 and PA18 (Arduino pins 12 and 10 respectively) to act as inputs for 2 different signals entering the device. The first is connected to a reed switch with an external 4.7k ohm pull up resistor with the reed switch connected to ground. The second is connected to a LDO's output to detect if a device external to the PCB has been powered on (schematics attached). This is attached to a 4.7k ohm pull down resistor. The issue I'm having is that after a few hours of operation, the micro begins to not accurately detect if these sources are high or low. Checking with a multimeter, I've noticed the voltages at the inputs are 1.53-ish volts for the reed switch and 1.23-ish volts for the LDO, rather than the standard 0v or 3.3v. Does anyone know what could be causing this and how I'd fix it?

Thanks

[DrAzzy]

Did you forget to connect the grounds?

[tyguy2]

Did you forget to connect the grounds?

No

[TomGeorge]

Hi,
Did you check the 3.3V at the pullup resistors?

How far away is the reedswitch and the LDO?
Do you have a scope to look at the inputs?
If not, what voltage do you measure on the inputs with your DMM in AC mode, before and when the fault occurs?

Thanks.. Tom..