External input source is not detected in GPIO.pulldown mode

Salahuddin Asjad · ‎2017-09-25

Posted on September 25, 2017 at 21:07

Hi,

I am currently working on a project that involves a STM32 F4 Discovery board where I am trying to use an external input source as the input to the GPIO pin. The external input source is a power supply set to 3.3V. The pins are set to mode GPIO_PULLDOWN such that the input is grounded when no particular value is assigned. However I am unable to change the input value once it is grounded. When I set the power supply to give 3.3V to the input pin, it still stays grounded. But when I connect a 3.3V pin on the board to the input pin, it gets 3.3V as input. I have noticed one thing, which I find a bit strange: when I use a multimeter to measure the input pin, the multimeter measures 3.3V on the input pin when I use GND from the power supply and the VCC from the input pin. But when I use the GND pin from microcontroller and VCC from the input pin, it outputs 0V.

Any idea how I can solve this? Thank you in advance.

#gpio #input #gpio-pullup-pulldown #stm32-f4-discovery #gpio-3.3-5-volt-stm32f4discovery

waclawek.jan · ‎2017-09-26

Posted on September 26, 2017 at 09:46

I don't quite understand: do you use an external power supply to power the DISCOVERY board? Where exactly you have the GND of that power supply connected?

JW