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Measuring RPM

Discussion in 'General Electronics Chat' started by Tobias, Mar 26, 2009.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
    Three methods I can think of at the moment
    1. Count pulses over a set amount of time. This takes up time that I can be doing other commands.

    2. Measuring the high or low pulse. Seems like a good deal.

    3. Frequency to voltage converter. I just found this online today. I found National Instruments LM2917. Needless to say I am not familiar with this device yet I understand that I can read the voltage out and know quickly RPM.

    I am working on making a piece for a race car where the RPM will be 0-10000 with 8 counts per rev. Will I be able to adjust the LM2917 to output 0-5v to represent the 0-10000?
  2. leftyretro

    Active Member

    Nov 25, 2008
    That chip, if you can find it as I'm not sure it's in production, should be able to do the job. Your speed/pulse requirements works out to be a 1.333 khz maximum rate which is well within the chips capablity. The scaling of voltage input to 10,000 display at max is something you handle in the software programming and is not a problem.

    Still it would be cheaper to do it with just inputing the speed pickup pulses as a digital input signal that generates a interrupt where it keeps track of the pulses per set time interval and generates a new RPM variable on a continous basis. That can work independently of your main program which would be free to do other tasks as well.