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Digital panel meters

Discussion in 'General Electronics Discussion' started by steveplant123, Mar 28, 2013.

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  1. steveplant123

    steveplant123

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    Mar 28, 2013
    I am building a very simple bench power supply based around the LM317 chip (2amp version)
    I want to monitor output voltage and current with a couple of digital LED modules.
    I have powered these using a second (100mA) LM317.

    The problem I get is that I get a 'dead short' when the ammeter module is in the circuit. (whichever way I connect it in)
    Also the DVM module will not read the correct value!

    The only way I can get the system to work correctly is by powering the Voltmeter and Ammeter with separate 9V batteries.(which does demonstrate my PSU wiring is correct!)

    As I really don't want to use batteries any suggestions as to how I can power these two meter modules without them 'interfering' with each other would be much appreciated.

    Please be aware that my knowledge of electronics is very basic (as is probably demonstrated by this question!)

    Many thanks in advance, Steve P
     
    Last edited: Mar 28, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    It may be possible to make the ammeter inputs float.

    If not, it may be possible to read the current in the ground wire.

    If not, it may be possible to get a small *ISOLATED* DC-DC converter to provide a fully isolated rail for the ammeter.
     
  3. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Please don't be insulted by this question, but you are not trying to connect the ammeter across the output, are you?

    Bob
     
  4. steveplant123

    steveplant123

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    Mar 28, 2013
    Worked!

    Thanks for your advice. The simple change to using the negative line solved both problems!
    Said my electronics knowledge was 'basic'
    Cheers, Steve P
     
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