Reading a speed sensor on L432KC Nucleo

[xpp07]

I'm using a reed switch (a pulse per revolution) to measure the speed of a wheel. The sensor output is connected to PA12 which is TIM1_ETR pin. I connected it there by mistake in my final PCB. I would have to tweak the PCB if I want to change timer channel.

Is there a way that I can measure speed on this pin?

[Tesla DeLorean]

Configure TIM1 in External Count mode, using TIM1_ETR.

Set counter in maximal mode (TIM1->ARR = 0xFFFF), and then read the counter TIM1->CNT once a second, and subtract out the count from the prior read. Do the math using uint16_t variables.

[xpp07]

Sorry for this question .. but I forgot to mention that channel 1 from Timer1 (PA8) is used as PWM generation. Does this affect what you explain above? I'm just starting to get involved with STM32 and CubeMx

[Tesla DeLorean]

So if you can't use it as a TIM input, consider using PA12 as an EXTI, generating an interrupt for each pulse.

[xpp07]

So I think that I can set PA12 as an EXTI and update a variable each time the pulse is given. But I would need the time elapsed between pulses. Is there a way to find it out?

[Tesla DeLorean]

To what accuracy?

You could have TIM2 counting elapsed microseconds.

Or frankly just have the EXTI increment a counter you check every second or millisecond.

Sorry you don't mention a range of speeds/frequencies involved. ​

[xpp07]

It's low RPM application. The reed switch is located in a treadmill. I don't have the exact range of speed, but motors I'm using are around 3000 RPM max. Of course, this limit is not reached in treadmill applications