Using RPM input as a hardware counter



  • Hi, what are the speed capabilities of the RPM input pin (PB6)? I'm using a Duet3 on a project and have need to count pulses coming from an external device. From what I've found online, the Duet doesn't directly work as a hardware counter or straight tachometer, but many folks have used the RPM input pin for that reading. My input signals could be as fast as 25MHz. How fast can the Duet3 keep up with?

    As background, I did find this in the forums already related to connecting to the PB6 pin for counting: "Connect the tacho wire through a diode (1N4148 or similar should work) to pin PB6 on the expansion connector. The cathode of the diode (the end with the stripe) goes to the tacho wire." Thanks.


  • administrators

    @TommyHawkins said in Using RPM input as a hardware counter:

    Hi, what are the speed capabilities of the RPM input pin (PB6)? I'm using a Duet3 on a project and have need to count pulses coming from an external device. From what I've found online, the Duet doesn't directly work as a hardware counter or straight tachometer, but many folks have used the RPM input pin for that reading. My input signals could be as fast as 25MHz. How fast can the Duet3 keep up with?

    To measure a signal as fast as 25MHz, you need to use a dedicated peripheral in the microcontroller. That could be either one of the timer/counters, or the frequency meter peripheral found in some more recent processors. Perhaps one of these https://www.adafruit.com/product/3800.


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