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FEke
FEke
Visitor II
June 16, 2019
Question

Quadrature encoder integration

  • June 16, 2019
  • 1 reply
  • 934 views

Hi there

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I​ am trying to integrate a quadrature encoder using STM32 cortex m mcus.

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I could not get enough clearance reading the manual several times. I don't have an oscilloscope, which is why I need to rely on specifications rather than trial and error.

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So far, i have been able to run the Tim/encoder example code to read the direction of turn (tim3 on stm32f401re).

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What I want to do is to

1) read the relative position since beginning​ (tim3 or timx /= tim3?)

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2) use a secondary timer to read frequency of the square wave to derive speed with hardware (tim4) counting. I have read the example on input capture for pwm input, but I only need the frequency and the master slave is done inside the same timer there. I want to make tim4 slave to tim3

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OR

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Should I simply attach the same encoder signal additionally to a Tim 4 pin directly​ and get rid of master slave conf?

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3) similarly derive acceleration (tim4 or tim5)

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4) do all that as precise as possible with the given hardware

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Here are my questions..

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1) Can the timer which uses the encoder mode to get direction (which disables use of slave/master conf for other uses) be also used to get the relative ​position?

OR

​do I need to use a separate second timer for position as well?

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2) how can I setup a timer as a slave in depicted cases?

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Any help is much appreciated!

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Best regards

This topic has been closed for replies.

1 reply

waclawek.jan
waclawek.jan
Super User
June 16, 2019

1) > Can the timer which uses the encoder mode to get direction (which disables use of slave/master conf for other uses) be also used to get the relative ​position?

Yes. You should have the two signals connected to CH1 and CH2 of given timer, enabled them for input by setting both respective TIM3_CCMR1.CCxS to 0b01, setting the slave-mode controller to encoder i.e. TIM3_SMCR.SMS=0b001, or 0b010, or 0b011; and finally enabling the counter by TIM3_CR1.CEN=1.

2) > how can I setup a timer as a slave

You want to output the waveform coming into TIM3_CH1 as TRGO (trigger out) (CH2 or any other channel set as input can't be used as TRGO), i.e. set TIM3_CR2.MMS to 0b011. Then in chapter for TIM4, look at table at the end of description of TIMx_SMCR to find out which ITR input corresponds to TIM3->TIM4, for 'F407 it's ITR2 and I guess it's the same for 'F401; so set TIM4_SMCR.TS to 0b010. Then, by setting any TIM4 channel's TIM4_CCMRx.CCxS to 0b11 (and enabling it in TIM4_CCER.CCxE), that channel will capture at the pulses incoming through the TIM3->TIM4 link, i.e. at those coming to TIM3_CH1. Enable the counter (TIM4_CR1.CEN=1) with internal clock (ie. with TIM4_SMCR.SMS=0b000), and in the respective TIM4_CCRx you will find the timestamp for incoming pulses; you can set an interrupt for that channel and read it out there, or use DMA if you expect higher input frequencies.

JW

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