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Description
This is my Third tutorial in this series of using Input capture to measure different things. I have already covered how to measure the pulse frequency and Pulse width separately using input capture, so today in this tutorial I am going to show you how to do it combined i.e. measure the frequency and duty cycle of a PWM input signal.
I will be using STM32F103C8 controller and SW4STM IDE, But the code should work in any other STM32 microcontroller too.
How it works
Let’s go to the explanation along the CubeMx setup. Take a look at the Clock setup below
As you can see above that APB1 TIM clock is at 72MHz. Also the TIM Clock is PCLK1 x 2. This is going to be useful in a while. Let’s see the TIMER Setup now
As shown on the picture above here is the setup:-
- Slave Mode -> RESET Mode
- Trigger Source -> TI2FP2
- Channel 2 -> Input Capture Rising EDGE
- Channel 3 -> Input Capture Falling EDGE
- Prescalar -> 0
- ARR -> 0xffff
NOTE THAT the Prescalar is 0 this time so the TIM Clock will be 72MHz and as the ARR value is 0xffff (65536), The minimum frequency that we can measure will be equal to ((72 MHz)/65536) = 1098 Hz.
Also Channel 2 is configured for the rising EDGE so it’s better if you connect the input PIN to the CHANNEL 2.
Some Insight into the CODE
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1 |
IC_Val1 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_2); |
Captures the first TIMESTAMP when the Rising edge is detected and stores it in the variable IC_Val1. This value corresponds to the “Time Period” of the pulse.
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1 |
IC_Val2 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_3); |
Captures the first TIMESTAMP when the Falling edge is detected and stores it in the variable IC_Val2. And (IC_Val2/IC_Val1) value corresponds to the “Duty Cycle” of the pulse.
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1 2 |
Duty_Cycle = (IC_Val2*100/IC_Val1); Frequency = (2*HAL_RCC_GetPCLK1Freq()/IC_Val1); |
Frequency can be calculated using the IC_Val1. Here (2* HAL_RCC_GetPCLK1Freq) is for the reason that the TIM2 CLOCK is 2x PCLK1.
CODE
| You can download the entire code at the end of this article.. |
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void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim) { if (htim->Channel == HAL_TIM_ACTIVE_CHANNEL_2) // rising edge interrupt { // read captured value IC_Val1 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_2); // first value if (IC_Val1 != 0) // if the value is not 0 { // read second value IC_Val2 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_3); // falling edge value // calculate Duty cycle Duty_Cycle = (IC_Val2*100/IC_Val1); // calculate frequency Frequency = (2*HAL_RCC_GetPCLK1Freq()/IC_Val1); // As my timer2 clock is 2X the PCLK1 CLOCK that's why X2. } else { Duty_Cycle = 0; Frequency = 0; } } } int main(void) { HAL_Init(); SystemClock_Config(); MX_GPIO_Init(); MX_TIM2_Init(); MX_I2C1_Init(); lcd_init (); // start the IC in interrupt mode HAL_TIM_IC_Start_IT(&htim2, TIM_CHANNEL_2); HAL_TIM_IC_Start_IT(&htim2, TIM_CHANNEL_3); while (1) { // Print these values on the LCD lcd_send_cmd (0x80); lcd_send_string ("FREQ= "); lcd_send_data ((Frequency/100000)+48); // print 6th digit lcd_send_data (((Frequency%100000)/10000)+48); // print 5th digit lcd_send_data (((Frequency%10000)/1000)+48); // print 4th digit lcd_send_data (((Frequency%1000)/100)+48); // print 3rd digit lcd_send_data (((Frequency%100)/10)+48); // print 2nd digit lcd_send_data (((Frequency%10))+48); // print 1st digit lcd_send_cmd (0xc0); lcd_send_string("DUTY= "); lcd_send_data ((Duty_Cycle/100)+48); // print 3rd digit lcd_send_data (((Duty_Cycle%100)/10)+48); // print 2nd digit lcd_send_data ((Duty_Cycle%10)+48); // print 1st digit lcd_send_data('%'); HAL_Delay (10); // wait for some time } } |
Result
| You can check out the Video below |
You can buy me a coffee sensor 🙂
Or just Download the code below
Sir, In your code IC_Val2, is not getting updated. Hence duty cycle is zero. Also How falling is detected?