Voltage Indicator - Op-Amp, Zeners Or?

Discussion in 'The Projects Forum' started by uponone, Mar 10, 2011.

  1. uponone

    Thread Starter New Member

    May 18, 2010

    I am hoping someone can help me out with a voltmeter circuit I am working on. The purpose of this circuit is to monitor a 7.2V battery. I do not want to use an external power source to run the unit and since I am trying to keep this as cheap as possible I would like to avoid the LM3914.

    This circuit will light 4 leds at the following voltages:

    7v - green led on
    6v - green led on
    5v - red led on
    4v - red led on

    (I want to use a bar type mode not dot)

    I am new to electronics so bare with me if my questions seem silly.

    From the research I have done on Google, it seems I should be using a LM324 op-amp but I am confused because some sources say this MUST be used with a separate power supply. Is this true? I have attempted to read the datasheet for LM324 but it is over my head.

    I have found this schematic that seems to be what I need:


    Can I use this? If so, what would I need ot modify in order to measure the specified voltages and change the input to 4-7.2v? I am still wrapping my head around voltage dividers so I haven't been able to calculate the correct resistors. I would also like to get rid of the trim-pot if possible.

    Would I be better off using some zener diodes to construct this ciruit?

    Thanks for the help,
  2. jean_all

    New Member

    Mar 8, 2011
  3. uponone

    Thread Starter New Member

    May 18, 2010
    Hi jean_all,

    Thanks for taking the time to reply. That comparator looks promising. Do you know if they manufacture a 4-channel version?

  4. beenthere

    Retired Moderator

    Apr 20, 2004