Frequency to voltage conversion

Discussion in 'The Projects Forum' started by The_big_dill, Oct 19, 2014.

  1. The_big_dill

    Thread Starter New Member

    Jan 5, 2013
    10
    1
    Hi all,

    I am working on a project where I am driving LEDs based on the RPM of an engine.

    It isn't the typical method where you just listen to the ignition events of a coil, rather, it is coming from a standalone ECU that outputs 0-12V square wave (frequency depends on RPM).

    I know I can use the LM2917 to do this conversion, however, I am not able to simulate it in Multisim. I tried looking up the circuit diagram for that chip, but I don't know how I would immitate a "charge pump".

    In any case, I hope someone has some insight into my options or has a solution.

    Thanks,

    Phil.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    You can breadboard the LM2917 circuit per the app. notes without simulating it...
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,220
    This might help. The .sub file is the model file. You'll likely have to do your own schematic symbol for Mulisim.
     
  4. The_big_dill

    Thread Starter New Member

    Jan 5, 2013
    10
    1
    I will see what I can do with this, Thanks.

    Any other options besides using the LM 2917 chip?
     
  5. The_big_dill

    Thread Starter New Member

    Jan 5, 2013
    10
    1
    I am not sure what you mean. But if you are saying that I should test it on the board without simulating it in the program first, then I don't really like that option because I want to be able to show this design on paper.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    If you would rather not use the LM2917, you can get the same functionality, though with lower linearity by merely triggering a monostable multivibrator with the signal from the ignition coil, then low-pass the output of the monostable.

    To obtain good linearity, pulses out of the monostable should be a couple tens of percent of the shortest period (at the highest RPM) that the circuit would encounter.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,026
    I built one of those, a 555 frequency to voltage meter. It was in the Forrest Mims booklet on the 555. It worked quite well. I fed it tones from my guitar tuner and the output voltage was quite linear in that range.
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    The LM331 can be fun as a frequency to voltage converter and only requires a few capacitors and resistors to function.
     
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