12V Tester

Discussion in 'General Electronics Chat' started by Webby, Nov 25, 2009.

  1. Webby

    Thread Starter Active Member

    Jun 15, 2008
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    0
    Hi all, I took my 12v tester appart last week and basically trying to work out how it all works. Just curiouse thats all.

    Inside the handle part which is clear there are two LEDS one red for positive and a green one for earth testing. They seem to be wired together with a resitor one end which then is connected to earth. The other end of the circuit is connected to the tip of the tester just wondered how it was all working thats all.

    Can anyone help here.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It probably is wired like this:

    [​IMG]

    If the polarity is correct, the green LED lights up.
    If the polarity is backwards, the red LED lights up.
     
  3. Webby

    Thread Starter Active Member

    Jun 15, 2008
    66
    0
    Hi Sgt, just wondered which way the LEDS were wired up, as two of the ends are wired together.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The green LED has its' anode towards the +probe, and its' cathode towards the -probe.
    The red LED has its' anode towards the -probe, and its' cathode towards the +probe.

    The resistor can be on either side (+ or -) of the LEDs, but it has to be in there somewhere; otherwise they would receive far too much current and burn up.
     
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