Improve this diagram

Discussion in 'General Electronics Chat' started by Razor Concepts, Nov 20, 2009.

  1. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008

    There are four coils that sense EMF and light up some LEDs accordingly. However from some comments I have read, whoever made this has made some errors. So far here is what I have spotted:

    1. No current limiting resistor for LED
    2. R4 is wasting power, it should be removed

    Anything else? Thanks!
  2. SgtWookie


    Jul 17, 2007
    That schematic is so bad even I can't believe it.

    It looks like he started out with a circuit designed for an LM339 comparator (which has open-collector outputs, thus requires a pull-up resistor on the outputs) and slapped in an LM324, which doesn't require pull-up resistors.

    The feedback resistors are so large in value they may as well not be there.

    The noninverting inputs are set to +V/2 by R1/R5 so unless the inputs exceed that, the outputs will never go high.

    As you mentioned, the LEDs need current limiting resistors.

    The schematic is so poorly drawn that it detracts from a good analysis of what the original intent was.
  3. Wendy


    Mar 24, 2008
    I think you called the key mistake, he substituted a LM339 with a LM324. If that were the chip used then the pullup resistors would be the current limiting resistors for the LEDs, and valid.
  4. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
    OK, so it looks like I am better off making a circuit from scratch.

    I am thinking about this, the coil is put on the input of a divided feedback circuit, and that boosts the voltage to a higher level (5v?), and that voltage is put through a voltage to current circuit, which lights up an LED accordingly. Does that sound feasible? Thanks!