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sanju
sanju
Associate III
March 27, 2018
Question

PWM with first pulse different

  • March 27, 2018
  • 2 replies
  • 1174 views
Posted on March 27, 2018 at 07:56

Hello everyone,

I am just new to stm32 microcontroller. I am starting my first project of stm32 using “STM32F030C6T6� MCU. My project is to drive a “high speed solenoid valve driver�.

In which I have to drive a mosfet with PWM of duty cycle 15%@40Khz. Till this point it is not a problem. but there is a twist that first pulse of PWM output must be of 500ms period i.e. 2Hz with approx. 80% duty cycle means 80%@2Hz. From 2nd pulse it should be then 15%@40Khz

Just Summarizing here:

__1st pulse : Freq. 2Hz, Period 500ms, duty cycle appr. 99%

2nd pulse: Freq. 40KHz, Period .025ms, duty cycle appr. 15%

3rd pulse: Freq. 40KHz, Period .025ms, duty cycle appr. 15%

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last pulse: Freq. 40KHz, Period .025ms, duty cycle appr. 15%

Note: Toff of all pulse from first to last should be same.__

Can any one help me how it can be done with timer or how to configure timer for it.

You feedback and suggestions will be highly appreciated.

Thanks in advance.
    This topic has been closed for replies.

    2 replies

    waclawek.jan
    waclawek.jan
    Super User
    March 27, 2018
    Posted on March 27, 2018 at 09:44

    Set both TIMx_ARR and TIMx_CCRy to preloaded (TIMx_CR1.ARR=1, TIMx_CCMRz.OCyPE=1). Set TIMx_CCMRz to required output mode and enable in TIMx_CCER . Set TIMx_PSC, TIMx_ARR and TIMx_CCRy for the first pulse and set TIMx_EGR.UG to generate an update to make those settings active. Now set TIMx_PSC, TIMx_ARR and TIMx_CCRy for the subsequent pulses - these will get active only after the first cycle is finished and next Update is generated during the run of timer. Now enable the timer by TIMx_CR1.CEN.

    If the desired number of pulses is below 256, you can use TIM1 and its repetition counter (TIM1_RCR) and one-pulse mode (TIM1_CR1.OPM) to automatically stop the timer after the set number of pulses; but in TIM1 also don't forget to set TIM1_BDTR.MOE to enable outputs. Otherwise, you'd need to stop the timer in software when the required number of pulses elapsed (using an interrupt).

    JW

    sanju
    sanjuAuthor
    Associate III
    March 27, 2018
    Posted on March 27, 2018 at 10:56

    Thank you so much dear for your immediate reply. I got your suggestion, I will do it in my code and will let you know if I encounter any problem.

    By the way one mistake I have done while putting this question, that the frequency for first pulse is 2.0khz not 2hz. But no a problem I will calculate values as per this and will write the code.

    Once again thank you so much.

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