PWM controlled ammeter question?

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.]

using a simple op-amp with the + connected to the arduino output, the negative biased to 2.5V ish (You could use a pot to get it better), then supply the opamp with +- 15V (Easier than trying to use a rail to rail opamp or do it with transistors)

this will provide you with the +- swing nice and easy. you could also use a simple analogue comparitor the schematic would look the same

Use an instrumentation amplifier such as INA826, which is a rail to rail device. Power it from +/-12V. Set the gain to give +5V in +24V out but set the Vref to -12V to shift the output range down to +/-12V.

Here is very simple way to convert 0-5 V PWM to -2.5 to +2.5 V (avg value) converter..

the circuit below is just high pass filter which remove DC portion of PWM to make it negative and positive both..

the circuit will not work at 0% or 100% duty cycle but works just fine in range of 1% to 99% duty cycle..

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

Thanks Peter.  i do have some op amps at home i can try and use, maybe even some comparators.  i will give this a shot tonight.  ohh and by the way I really enjoy your you tube channel!

Mark

That sounds like a great idea and simple, i will need to get that chip though.  At this point i am hoping to use what i have at home, several opamps, transistors.  Thanks for your input!

Wow, that would really make it simple.  i will give that a shot!  thanks so much!

Is it easier than doing it with transistors? The above isn't a whole lot more complicated than using an op-amp (plus you don't have the problem of trying to trim the zero and getting the gain right for the full-scale deflection.)