Frequency to voltage converter lm2907 ground connection

Discussion in 'General Electronics Chat' started by Tony Elliott, Nov 15, 2015.

  1. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Hello All About Circuits,

    I am using a square wave oscillator 555/4013 (powered by 9v battery) connected to a LM2907 frequency to voltage converter (12v - ground +).

    I have taken the positive from the audio out and put it into the frequency in (Fin) as you can see in the schematic. I am getting a responsive reading on my multimeter (by varying the oscillators frequency) without ground connected from audio out. 0 - 1.8 khz 1 - 2.4 dc
    When I connect ground I get nothing. On the schematic, frequency in (Fin) am I doing something wrong in my connections??

    circuit on page 10
    http://www.ti.com/lit/ds/symlink/lm2907-n.pdf
     
  2. Veracohr

    Well-Known Member

    Jan 3, 2011
    550
    75
    I've never used something like this so I'm not sure, but you've got -12V on the negative input to the comparator so I wonder if it is able to do anything. Your input signal doesn't go below -12V does it? With the circuit connected as shown in the datasheet, the negative comparator input is ground, so it is sensing the 0-crossing point of the input signal.

    Try removing the -12V and just ground those pins like the circuit in the datasheet.
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Are you really using a +/- 12V (24V total) power supply?
     
  4. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    It doesn't go below -12v. What you said sounds interesting. You mean attach the ground from the 9v circuit to the -12v in the comparator? I'll try it
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    The reason I asked the question was that some will tag a voltage as though it were the negative end of a battery, ie a single 1.5 volt cell will have a +1.5V and a -1.5V. Throwing a ground into the mix will require TWO 1.5v cells. Just to clarify, do you indeed have a +12, GND and -12 supply?
     
    Tony Elliott likes this.
  6. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Yes I'm using a adjustable voltage supply as seen in the picture.
     
  7. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    I tried doing this and there was no voltage reading.
     
  8. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    I think Ive solved this, I turned the 9v battery oscillators power into two 9v batteries with 100 uf capacitors and made it into a dual battery power with - ground + and attached the ground between circuits and I have a much more stable reading on my multimeter.
     
  9. Veracohr

    Well-Known Member

    Jan 3, 2011
    550
    75
    No, I meant don't use the -12V supply. Replace it with ground (common from your +-12V supply), to which you would also attach the negative terminal from the battery. There's no reason to use the -12V supply, only the +12V.
     
  10. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Ah I see what you mean, I'll try this and get back with the results:)
     
  11. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Yes you were right I used the ground from the 12volt supply with the battery circuit using only one battery instead of two, it worked when I put the ground where the minus and the minus where the ground is on the battery circuit strange really? I used 104 capacitors to bridge to smooth
     
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