How to measure frequency using Timers

[Arman Ilmak]

Posted on June 05, 2018 at 22:30

Hello guys.

When I used LPC17xx series in my last experience of ARM MCUs I used 2 timers one for generating interrupt every 1 second and one for counting the rising edges of the input CAP.

So I started reading the Reference menu of the stm32F2xx ,but there were a lot of timer functions described in timer section.I was confused which one to use for my purpose.

Now I know that how to set the timer to work as a TIME BASE,but for input I didn't know which one to use.One section described external clock mode 1 and the other external clock mode 2 and the other was input capture mode .

Which one should I use?

#stm32f2 #cube-hal

[henry.dick]

Posted on June 08, 2018 at 02:22

'

Which one should I use?'

it depends on what you are trying to do.

The basic form of measuring frequency is to compare / gate two pulse trains, one of unknown frequency, and another of known frequency. 

1) the typical way is to use the known pulse train to generate a time base that turns on / off the counting of the unknown pulse train; this works for high frequency signal;

2) it can also be done the other way around: using the unknown pulse train to gate the known pulse train -> aka a reciprocal counter; it works for lower frequency measurement.

3) for cases where you don't need super high precision and the input pulse train isn't too fast / slow, you can use input capture to measure the frequency as well.

there are other ways too. all depends on what kind of signal you are trying to measure.

[Tesla DeLorean]

Posted on June 08, 2018 at 01:33

Sorry don't use CubeMX

The PWMInput examples should use CH1 and CH2 to report period and duty, and reset

STM32Cube_FW_F4_V1.21.0\Projects\STM32F4-Discovery\Examples\TIM\TIM_PWMInput\Src\main.c

  /*♯♯-1- Configure the TIM peripheral ♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯*/

  /* Set TIMx instance */  TimHandle.Instance = TIM2;

  /* Initialize TIMx peripheral as follow:

       + Period = 0xFFFFFFFF       + Prescaler = 0       + ClockDivision = 0       + Counter direction = Up  */  TimHandle.Init.Period = 0xFFFFFFFF;  TimHandle.Init.Prescaler = 0;  TimHandle.Init.ClockDivision = 0;  TimHandle.Init.CounterMode = TIM_COUNTERMODE_UP;  if(HAL_TIM_IC_Init(&TimHandle) != HAL_OK)  {    /* Initialization Error */    Error_Handler();  }

  /*♯♯-2- Configure the Input Capture channels ♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯*/

  /* Common configuration */  sConfig.ICPrescaler = TIM_ICPSC_DIV1;  sConfig.ICFilter = 0;

  /* Configure the Input Capture of channel 1 */

  sConfig.ICPolarity = TIM_ICPOLARITY_FALLING;  sConfig.ICSelection = TIM_ICSELECTION_INDIRECTTI;  if(HAL_TIM_IC_ConfigChannel(&TimHandle, &sConfig, TIM_CHANNEL_1) != HAL_OK)  {    /* Configuration Error */    Error_Handler();  }

  /* Configure the Input Capture of channel 2 */

  sConfig.ICPolarity = TIM_ICPOLARITY_RISING;  sConfig.ICSelection = TIM_ICSELECTION_DIRECTTI;  if(HAL_TIM_IC_ConfigChannel(&TimHandle, &sConfig, TIM_CHANNEL_2) != HAL_OK)  {    /* Configuration Error */    Error_Handler();  }  /*♯♯-3- Configure the slave mode ♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯*/  /* Select the slave Mode: Reset Mode */  sSlaveConfig.SlaveMode     = TIM_SLAVEMODE_RESET;  sSlaveConfig.InputTrigger  = TIM_TS_TI2FP2;  if(HAL_TIM_SlaveConfigSynchronization(&TimHandle, &sSlaveConfig) != HAL_OK)  {    /* Configuration Error */    Error_Handler();  }

  /*♯♯-4- Start the Input Capture in interrupt mode ♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯*/

  if(HAL_TIM_IC_Start_IT(&TimHandle, TIM_CHANNEL_2) != HAL_OK)  {    /* Starting Error */    Error_Handler();  }

  /*♯♯-5- Start the Input Capture in interrupt mode ♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯♯*/

  if(HAL_TIM_IC_Start_IT(&TimHandle, TIM_CHANNEL_1) != HAL_OK)  {    /* Starting Error */    Error_Handler();  }