GPIO output level consistency issue

[jgauthier]

Hello,

I have three GPIOs output configured. I'm having some strangeness on two of these that I don't quite understand.

I'm using a nucleo STM32L432KC, and I have some custom circuitry attached to the GPIOs (detailed below)

The situation I am experiencing is as follow.

When I set the 3 GPIOs like so, I have expected results.

HAL_GPIO_WritePin(GPIOB, GPIO_PIN_7, GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_SET);

PB7,PA5 are low and PA6 is high.

The next condition I test:

HAL_GPIO_WritePin(GPIOB, GPIO_PIN_7, GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_RESET);

Should show PB7 low, PA5 high ad PA low.

But instead I see this:

PA5 appears to be bouncing all over the place, and once in a awhile PB7 does as well.

(This is short sample, of like 5 seconds)

Finally, when I do this:

HAL_GPIO_WritePin(GPIOB, GPIO_PIN_7, GPIO_PIN_SET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_RESET);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_RESET);

I see these results:

Both PB7 and PA5 are high, and steady.

Each circuit is tied to a 10k pulldown resistor.

PA6

PA5

PB7

 

I don't quite understand a) why won't PA5 stay up, and how is PB7 somehow tied to PA5.

If anyone has some ides, I'd appreciate it.

[Peter BENSCH]

The npn bipolar transistors are current driven and emitter followers, so you'd need some load connected to them. What is connected at the outputs?

Regards

/Peter

[jgauthier]

I didn't have a load, actually. But I attached my intended load. Which are 2 24V solenoids (relays not pictured)

The behavior is the same regardless. So, I am still hunting - maybe it's hardware issue.

[Michal Dudka]

1) Check output voltages by oscilloscope (or multimeter). Probably there are "analog" values.

2) Check your GPIO settings (are GPIOs outputs ? in push-pull mode ?)

3) Check HW for short circuits (bad soldering)

[jgauthier · Accepted solution]

Thanks! I finally figured it out,

PA and PB7 are directly connected through solder bridge on the Nucleo. I removed the bridge.