STM32L031 reading 5 digital Inputs work fine, but doing the same with 10 inputs fail.

[Hugo Balette]

Posted on November 16, 2017 at 11:32

Hi !

I'm working on a STM32L031 project, and I need to read 10 digital 0V-3v3 Inputs.

Everything works fine if i'm reading 5 inputs (PA3, PA4, PA5, PA6, PA7). It is also working if I'm reading 5 other inputs (PB3, PB4, PB5, PB6, PB7).

But as soon as I plug both PA3, PA4, PA5, PA6, PA7 and PB3, PB4, PB5, PB6, PB7, it stops working.

I checked using a voltmetre in the 10 inputs config, and 4 inputs don't rise to 3v3, but only 1V.

So It only reads 3 inputs of (PA3, PA4, PA5, PA6, PA7) and 3 inputs of (PB3, PB4, PB5, PB6, PB7).

Would it be a problem of current sinking ? or just a wrong software configuration ?

I tried configuring inputs with and without pull down.

I checked GND is common to every inputs.

Any ideas ?

thanks for your time.

Hugo

#current-sink #digital-input #stm32l0 #3v3

[AvaTar]

Posted on November 16, 2017 at 11:39

Instead of guessing, it would be better if you presented at least the init code for those ports.

I guess you missed something, perhaps enabling port B.

[Hugo Balette]

Posted on November 16, 2017 at 11:45

Ok AvaTar, thanks for your quick response.

Here is my init code :

static void MX_GPIO_Init(void) { GPIO_InitTypeDef GPIO_InitStruct; /* GPIO Ports Clock Enable */ __HAL_RCC_GPIOC_CLK_ENABLE(); __HAL_RCC_GPIOA_CLK_ENABLE(); __HAL_RCC_GPIOB_CLK_ENABLE(); /*Configure GPIO pins : Sensor_1A_Pin Sensor_2A_Pin Sensor_3A_Pin Sensor_4A_Pin Sensor_5A_Pin */ GPIO_InitStruct.Pin = Sensor_1A_Pin|Sensor_2A_Pin|Sensor_3A_Pin|Sensor_4A_Pin |Sensor_5A_Pin; GPIO_InitStruct.Mode = GPIO_MODE_INPUT; GPIO_InitStruct.Pull = GPIO_NOPULL; HAL_GPIO_Init(GPIOA, &GPIO_InitStruct); /*Configure GPIO pins : Sensor_5B_Pin Sensor_4B_Pin Sensor_3B_Pin Sensor_2B_Pin Sensor_1B_Pin */ GPIO_InitStruct.Pin = Sensor_5B_Pin|Sensor_4B_Pin|Sensor_3B_Pin|Sensor_2B_Pin |Sensor_1B_Pin; GPIO_InitStruct.Mode = GPIO_MODE_INPUT; GPIO_InitStruct.Pull = GPIO_NOPULL; HAL_GPIO_Init(GPIOB, &GPIO_InitStruct); }

I may have forget to precise something.

When I plug all of the 10 inputs, it don't work, but as soon as I unplug 5 of the 10 inputs, is works fine.

[S.Ma]

Posted on November 16, 2017 at 11:54

Where these pins are connected to? If they are floating, the voltage will be random (it's like GPIOs are 'antennas').

To prevent this, you can activate a weak pull-up on each pin so that when left unconnected, you will read a 1.

More fun: If you pull-up then pull-down (with few usec delay), you can guess the pin is left unconnected...

[Hugo Balette]

Posted on November 16, 2017 at 11:57

These pins are connected to a pulled-down signal.

The signal is rising to 3V3 when I get an event.

I already tried to enable pull-down during initialization, but it is the same problem. :\

Thanks for your help !

[S.Ma]

Posted on November 16, 2017 at 12:00

If you are using EXTI, you can only choose one pin per source: PB3 xor PA3, PB4 xor PA4.

If you want 10 pins, you shall use Px0 to Px9, some group of pins will share the same interrupt vector.