Trying to design a circuit to indicate servo motor rpm from duty cycle output

Discussion in 'The Projects Forum' started by Thespindoctor, Dec 29, 2014.

  1. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    I have a Teknic brand servo motor which outputs a 50 Hz signal. The signal has a duty cycle proportional to rpm ranging from 0 to 1000 rpm. Thanks for any suggestions to get me going on a circuit to display rpm!
     
  2. Brevor

    Active Member

    Apr 9, 2011
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    You could feed the speed signal into a low pass filter and drive an analog meter.
     
  3. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    Interesting, perhaps a much easier solution than I had imagined! Thanks, I will start looking at analog meters now!
     
  4. JohnInTX

    Moderator

    Jun 26, 2012
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    +1 on Brevor's suggestion. I regularly use 1ma meters marked 0-100% with a trimpot in series for calibration as a quick indicators for PWM outputs. Bought surplus for cheap. Pick a pot value that will give 1ma (or whatever your meter needs) at 100% PWM output with some adjustment for calibration. At 50hz, the meter inductance, motor back emf and needle inertia may give you all the filtering you need. If not, the suggested filter should do it.

    Have fun.
     
    Last edited: Dec 29, 2014
  5. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    It found quite a few analog meters that measure various ranges of DC voltage. I have a 5 volt signal with duty cycle such that 100% indicates 1000 rpm. I guess I could use a DC voltmeter 0-5v range and change the text on the meter to read 0- 1000 rpm instead of DC volts? I imagine that a circuit using a 555 timer and 7 segment displays might be cheaper. Many of the analog DC meters were more expensive than I was hoping for.
     
  6. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    Thanks! I did find some fairly inexpensive meters. Are the meters sealed or could take out the paper indicating 0-100% and print one of my own with rpm etc?

    My electronic knowledge is very limited. Does the trimpot take the voltage down to a range that the meter can handle as well as calibrate? I have a 5 volt DC signal.
     
    Last edited: Dec 29, 2014
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What kind of servo motor generates a 50Hz signal, where/how does it originate?
    Curious.
    :
    I think I see, it is a ECM or Electronically commutated motor with the controller built in by the look of it.
    Max.
     
  8. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    Yes, the drive is built in to the motor. I am very impressed with the motor and the documentation. I just wish they had a built in tachometer...
     
  9. JohnInTX

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    Jun 26, 2012
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    Lots of small meters can pop the front off for access to the scale. Some scale plates attach with screws and can be remarked. Ive scanned the plate then used photoshop to edit and print a new one.

    My example of a current meter required a 5Kohm series resistance to use with a voltage source. 5V FS/.001Amp mefer FS=5000ohms (not counting the small meter resistznce)

    A voltmeter with a scale of 5v would be ideal but maybe harder to find.

    Where are you located? If you sesrch for surplus electronic parts in your area you might get lucky. I bought mine for a couple of bucks each..
     
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  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is the exact model number of your motor?
    Max.
     
  11. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    I have a ClearPath Integrated Servo Motor CPM-MCVC-3421S-RLN
     
  12. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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    I would still love to have an 8 segment display for better visibility. I read about using the ICL7107 in a voltmeter circuit. Seems like a possibility if I could multiply the voltage by 200 and display that result. Lots more work than an analog meter. Think I will stick with the simple route... Thanks for all the input! I am sure I will have more questions when I get some parts together.
     
    Last edited: Dec 30, 2014
  13. JohnInTX

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    Jun 26, 2012
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  14. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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  15. Thespindoctor

    Thread Starter New Member

    Dec 29, 2014
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