Car Tachometer

Discussion in 'Circuits' started by Admin, Apr 17, 2013.

  1. Admin

    Admin Administrator Staff Member

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    This thread is for the discussion of the Car Tachometer circuit.
    Robert Gabb likes this.
  2. Robert Gabb

    Robert Gabb New Member

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    In the circuit description above the schematic diagram the meter is referred to as 50mA FSD, but in the paragraph below the diagram the meter is referred to as 0 - 1mA. This is a very important difference in trying to calibrate the circuit. Which is the correct meter 0-1 mA or 0-50mA ? Thanks.
    Rob.
  3. George

    George Moderator

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    I looked up a couple other ones on the net and found one that was 10V FSD meter and another that was 1mA FSD. I guess it would be best to check around and see if you can find another with the same pot hooked to it and go from there or just use a different design. Hope this helps a little.
  4. Robert Jelbart

    Robert Jelbart New Member

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    A milli-ameter in series with a resistor is a voltmeter. So don't go looking for a voltmeter. This circuit requires a 1 ma meter. The 200k pot makes it a voltmeter with a 200v range (!!). I would suggest that 10K (or 20K) would be more suitable

    50ma meter mentioned in the text must be a mistake. With the 200K pot set to it's mid position ( for example) it would require 5000v from the 555 to indicate FSD !

    As the 555 can source (or sink) 200ma probably it would work with 50ma meter - if you could find one - in which case the adjuster pot might be 470 ohms. But not recommended !

    The 4.7K resistor shown between the output and +v must be a mistake as well. Leave it out.

    But what do I know/ I'm just a drummer :)
    Last edited: Apr 18, 2014