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PWM controlled ammeter question?

Former Member

HI everyone,

 

i am trying to control a zero centered ammeter with a PWM signal from an arduino.  The ammeter displays a voltage from -12v to +12v where zero volts is in the center. The needle is centered when zero.  Now the Arduino can only supply a voltage from 0 to 5 volts simulated by a PWM signal with a value from 0 to 255, where 255 is the full 5 volts.  My problem is I need to drive the ammeter from a -12v to a +12v.  I'm thinking of some kind of external circuit with a transistor to switch on and off a 12 volt source, but that will only get me half the meter to swing.  How can I get a -12v to be driven by the Arduino?  I would like to supply a PWM value of zero to the Arduino pin which would correspond to -12v, and PWM value of 128 would be 0 volts on the ammeter, and PWM value of 255 would be +12v.  Hopefully this all makes some sense.  Any help would be appreciated!

 

THanks Mark

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  • 0

    You don't really need the -12V.

     

    If you connect the meter to your 12V supply it reads +12V.


    If you then swap the meter terminals, it will read -12V instead of +12V.

     

    So, you just need a circuit that does that for you. Think about the kind of H bridge circuit that people use to drive motors in either direction, only at a much lower current.

     

    Further thing to think about. Your volt meter is probably an ammeter with a series resistor to get full scale with 12V. If you can get at the resistor and replace it (if you felt confident you could do that without damaging the mechanism), you could convert it to be a 5V meter and then you wouldn't need the 12V supply. [An neater alternative to taking out the existing resistor might be to solder a second resistor in parallel with it to give the overall value you want.]

  • 0 in reply to jc2048

    Thanks Jon for your reply.  Yes i understand that it is just an ammeter with a series resister, but i do not want to modify the meter in any way.  Your idea about an H bridge did make me think.  Thanks

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