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Interfacing a PIR movement sensor to the STM32L-DISCOVERY using ChibiOS/RT

Jun 7, 2012

It is very easy to interface a Parallax PIR motion sensor to the STM32L-DISCOVERY board using ChibiOS/RT.

The sensor works with 3v, so we can use the 3v output from the discovery board to power it. Simply connect the output pin of the sensor to an I/O pin of the STM32 processor (I am using PA11). The sensor outputs a HIGH for a few seconds whenever it detects motion - this can be easily detected by reading from the I/O pin.

Here is a small program which lights up the blue LED on the discovery board whenever the sensor detects movement.

#include "ch.h"
#include "hal.h"

#define PIR 11

int main(void) {

  halInit();
  chSysInit();
  
  palSetPadMode(GPIOB, GPIOB_LED4, PAL_MODE_OUTPUT_PUSHPULL);
  palSetPadMode(GPIOA, PIR, PAL_MODE_INPUT);
 
  while (TRUE) {
    if(palReadPad(GPIOA, PIR))
      palSetPad(GPIOB, GPIOB_LED4);
    else
      palClearPad(GPIOB, GPIOB_LED4);     
    chThdSleepMilliseconds(10);
  }
}