LM2907 Tach circuit

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

  1. schwoch1

    Thread Starter New Member

    Feb 17, 2009
    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
    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
    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