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LM339 quad comparator question

  1. Mar 29, 2010 #1
    Hey all,

    I am trying to make a cheap ammeter for my power supply. My original plan was to use 10 series resistors to split a reference voltage from a +5 or +12V regulator.

    I was also going to place a .5ohm resistor in series with the final output. I planned on comparing the reference voltages with the with voltage across the resistor.
    - Vr +
    out ----|\|\|\|-----

    My problem is that 339 comparators have a single ground for the comparisons, if I were to connect the -Vr to ground, and the +Vr to the comparators V+, with the V- being the reference voltage, the whole thing would be messed up (in terms of difference between voltages).

    Does anyone know how I could compare the two signals using a common ground?



    edit: I think it may work if the resistor was instead connected between ground and the black power supply lead. Does anyone know if this would work?
    Last edited: Mar 29, 2010
  2. jcsd
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