Issue with Inputs Pins Sourcing Current

Troubleshooting
1

Hi,

I have a simple resistor divider network with the middle feeding to pin PB6/D1 of a P1 on a custom board. The divider is a simple divide by 2 with 4.5V at the top. When I configure the pin as an input with NO pull resistors, the output of the divider is reading 3V on a multimeter. Obviously this is not correct, it should be approximately 2.25V. I cut the trace between the divider and the pin and the output of the divider is now reading the correct value.

Does anyone know what might be causing this?

2

Update: The resistance between the trace and 3.3V seems to be 2.2k, the same as the I2C pull-up resistors. Is there a way to disable these or not?

3

There is no internal I2C pull-up resistor on the Photon, P1, Electron or Core. The STM32Fxx INPUT_PULLUP or INPUT_PULLDOWN resistor is around 40-50K and that’s only used when you set the pinMode to enable that.

4

Hi Rickkas,

Thanks for answering this. Where do you think the 2.2k could be coming from then?

5

No idea. It’s quite mysterious and hopefully someone else here will have an idea!