LM2907 Tach circuit

Discussion in 'General Electronics Chat' started by schwoch1, Feb 25, 2009.

  1. schwoch1

    Thread Starter New Member

    Feb 17, 2009
    2
    0
    HI All

    I need a little assistance on building a tach circut using the LM2907 IC
    I built 3 circuits one with the LM2907 chip one using the 555 timer circuit the other with just one transistor. All 3 worked out pretty good.The problem that I am having is the meter scale. the analog meter that I am using at full scale needs 50 MA. The input frequency that I am measuring is from 1500 th 2000 HZ 1500 HZ needing to be 0 on the scale and 2000 HZ needs to be 100% on the scale.lets say if I decrease my input frequency by 100 HZ I can move the needle from 100% to 90% But it really needs to move to !00% to 80% I need to move the needle more when I change the frequency. It also would be good it it the amount of needle movement on a frequency change was adjustable for calibration. Changing the gauge re scaling the gauge face is not an option the gauge offers the resolution that I need. any Ideas?
    Any input I can get on the problem would be very helpfull.

    Thank you Doug S
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It's the 50 milliamp meter movement. If you can use a more sensitive movement, or a voltmeter, you should have no problem. The 2907 has a voltage output - it's not designed to push current.
     
  3. schwoch1

    Thread Starter New Member

    Feb 17, 2009
    2
    0
    Hi All

    Changing the gauge or the scale is not an option. any other suggestions.
    Is there an IC or some type module that I can add to my LM2907 that will work


    Thanks Doug S
     
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