How to setup input capture mode for Maxbotix LV-MaxSonar using Pulse Width (Pin 2)

[ELith]

Hi I'm new to stm32Cube and have been trying for days to read these ultra sonic sensors. Here is the data sheet to the one i am using:

https://www.maxbotix.com/documents/LV-MaxSonar-EZ_Datasheet.pdf

if someone could please attach a picture of the stm32cube setup in order to read the Pulse Width (Pin 2) from the sensor i want the internal timer to start on the rising edge and stop/capture on the falling edge of the signal here is the setup i'm currently trying :

Any help would be much appreciated I'm very new to using timers and tried reading the timers cookbook but after 12 setup attempts i get an output that changes but i cant seem to figure out if i'm doing it right

this is my flag:

void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim) {
 
	if (htim->Instance == TIM2) {
		if (i == 0) {
			cap1 = __HAL_TIM_GET_COMPARE(&htim2, TIM_CHANNEL_1);
			i = 1;
		} else if (i == 1) {
			cap2 = __HAL_TIM_GET_COMPARE(&htim2, TIM_CHANNEL_1);
			i = 0;
		}
 
		__HAL_TIM_SET_COUNTER(&htim2, 0);
	}
}

and this is my while:

HAL_TIM_IC_Start_IT(&htim2,TIM_CHANNEL_1);
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
	  count = __HAL_TIM_GET_COUNTER(&htim2);
  }
  /* USER CODE END 3 */
}

 hers a snapshot of of output the values change i'm just no sure if it's right:

[Vangelis Fortounas]

hi,

prescaler value is too high.

suggest to put as prescaler value Tim2Freq/1000000 to have one microsecond resolution and to put at Auto Reload Register 0xffffffff ( the maximum value.)

there is no need to zeroize timer inside callback .

Save the two last captured values (as you already have done) and subtract the value cached by rise callback from the value catched by fall callback. (eg. cap2-cap1) The result will be in microseconds an you can convert it to inches by divide this by 147 (as writen in datasheet of the sonar)

[ELith]

Thank you vangelis i solved it thanks to that i changed my code it to have a 2 channels (1 direct on indirect) one for rising one for falling capture. The key to getting a nice looking output was as you said changing the prescaler to 72.