Display off-frequency with just LEDs ?

Discussion in 'The Projects Forum' started by Externet, Jan 28, 2015.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Hi all.
    How would you make the simplest possible analog sensing circuit that will turn a LED on if an inputted frequency is above 1KHz and another LED if the frequency is below 1KHz ?
    Does not matter if at 1 KHz both leds are on or off.
     
  2. #12

    Expert

    Nov 30, 2010
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    After about 2 minutes of thinking, a pair of filters starts with the question, "How sharp do you want it?"
    If you do a F to V converter and add a comparator at the DC level that represents 1KHz, that eliminates most of the filtering.

    Use a window comparator and, "How sharp do you want it?" becomes, "dial a Q".
     
    Last edited: Jan 28, 2015
    GopherT likes this.
  3. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Thanks, #12.
    The 1KHz frequency can be off about +/- 20 Hz before indicators take action.

    Do you know of any PLL IC that some pin will go negative or positive if deviated from the frequency ?
     
  4. #12

    Expert

    Nov 30, 2010
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    Ummm...no. Did you know there are F to V chips, and they are different from PLL's?
    I never built one of these, I'm just thinking of how a guitar tuner works.

    Yes, PLL chips go positive or negative when the input is not the center frequency. I just don't know the part number.
     
    Last edited: Jan 28, 2015
  5. ronv

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    Nov 12, 2008
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    Sine wave or square wave?
     
  6. MrChips

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  7. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Sine wave.
     
  8. GopherT

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    Nov 23, 2012
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    Use a comparitor on a Microcontroller, any signal that is more than 1000 microsecons between rising edges is less than 1000 Hz, anything faster is more. Adjust output to pin with appropriate LED.
     
  9. Reloadron

    Active Member

    Jan 15, 2015
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    There are a number of ways but my first thought
    That would be how I would do it. Not many parts and a few LEDs can be hung on the output. That or a GopherT suggest a micro controller.

    Ron
     
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