STM32F407 external frequency counting

[fueralle123]

Posted on October 16, 2013 at 11:17

Hello folks,

i have to try write a C-Code for counting an external frequency in a Range of 250ms. I tried to use the encoder mode, but i think it is impossible only with one signal. In my project i have only one frequency signal in a range of 0Hz to round about 400Hz. Could you help me or show examples how to count external frequency by using timer? Thanks a lot!! #stm32 #stm32 #timer #exti #interrupt

[Tesla DeLorean]

Posted on October 16, 2013 at 14:18

Well there are several methods, you can just do a raw count over some integration period, or you could use input capture or PWM input, these would permit period/duty type measurements.

[DEAD LINK /public/STe2ecommunities/mcu/Lists/STM32Discovery/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/STM32Discovery/STM32F4%20Timer%20External%20Pulse%20counting&FolderCTID=0x01200200770978C69A1141439FE559EB459D75800084C20D8867EAD444A5987D47BE638E0F&currentviews=134]https://my.st.com/public/STe2ecommunities/mcu/Lists/STM32Discovery/Flat.aspx?RootFolder=%2Fpublic%2FSTe2ecommunities%2Fmcu%2FLists%2FSTM32Discovery%2FSTM32F4%20Timer%20External%20Pulse%20counting&FolderCTID=0x01200200770978C69A1141439FE559EB459D75800084C20D8867EAD444A5987D47BE638E0F¤tviews=134

[fueralle123]

Posted on October 16, 2013 at 15:13

Hi Clive,

thanks for your replay, i include this part of code:

void TIM3_Config(void)

{   GPIO_InitTypeDef GPIO_InitStructure;   TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

  /* GPIOC clock enable */

  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);

  /* TIM3 clock enable */

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

  /* GPIOA Configuration: TIM3 CH1 (PC6) */

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN; // Input   GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;   GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;   GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;   GPIO_Init(GPIOC, &GPIO_InitStructure);

  GPIO_PinAFConfig(GPIOC, GPIO_PinSource6, GPIO_AF_TIM3);

  TIM_TimeBaseStructure.TIM_Period = 21000;

  TIM_TimeBaseStructure.TIM_Prescaler = 1000;   TIM_TimeBaseStructure.TIM_ClockDivision = 0;   TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;   TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;   TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  TIM_TIxExternalClockConfig(TIM3, TIM_TIxExternalCLK1Source_TI1, TIM_ICPolarity_Rising, 0);

  TIM_ITConfig(TIM3, TIM_IT_Update, ENABLE);

  TIM_Cmd(TIM3, ENABLE);

} maybe you can have a look??? Thanks a lot!!!

[Tesla DeLorean]

Posted on October 16, 2013 at 15:29

  TIM_TimeBaseStructure.TIM_Period = 21000;

  TIM_TimeBaseStructure.TIM_Prescaler = 1000; Why? Also these take N-1 values, but 400 Hz would easily fit in 16-bit

[fueralle123]

Posted on October 17, 2013 at 07:58

Oh okay, i thought i set the time to 250ms.

Can you explain me how i can set the time??

[Tesla DeLorean]

Posted on October 17, 2013 at 13:27

For that you'd need a second timer, or SysTick, to mark off the 250 ms sample period, and then do a delta measurement of clock ticks on the TIMx->CNT of your external source over the period.

ie freq = (b - a) * 4

[fueralle123]

Posted on October 17, 2013 at 15:16

Okay, but with your example on

[DEAD LINK /public/STe2ecommunities/mcu/Lists/STM32Discovery/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/STM32Discovery/STM32F4%20Timer%20External%20Pulse%20counting&FolderCTID=0x01200200770978C69A1141439FE559EB459D75800084C20D8867EAD444A5987D47BE638E0F&currentviews=134]https://my.st.com/public/STe2ecommunities/mcu/Lists/STM32Discovery/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/STM32Discovery/STM32F4%20Timer%20External%20Pulse%20counting&FolderCTID=0x01200200770978C69A1141439FE559EB459D75800084C20D8867EAD444A5987D47BE638E0F&currentviews=134 i'm able to count the signal? Thats right? Now i need a second Timer, which set the time (250ms) of the first timer/counter?

[Tesla DeLorean]

Posted on October 17, 2013 at 15:35

Why don't you try it? Then you'd be able to observe first hand what it does.

TIM3->CNT will represent your external count, it will keep counting up, and wrap at the 16-bit boundary. If it reads 123, and then 223 some 250 ms later it has counted 100 ticks, over a second this would represent 400, and thus 400 Hz There are other ways to gate the timer, or measure the individual period/duty, you might want to review the manual to understand the options.