Sink/Source panel meter

Not sure if this should go in electronics instead but I think I'm really asking about the design more than the way the electronics in this work...and sorry for the wordiness...I tend to over-describe :blush: I've got a couple center-zero panel meters, printed scale 0-1000 (http://www.ebay.com/itm/230691128247 - EIL 121H - the description states there are versions that go 0-1000 so don't let the picture throw you :)) I'm not looking to measure current for the sake of doing so - I'm just looking to use it as a physical display of other data (so the scale as written will be replaced with my own - leaving me to control the position.) With it being center zero I presume I need to reverse the current to display values left of center. Presuming the underlying measurement scale for the 0-1000 is 0-1000uA, can I just hook to 2 PWM pins, set both to OUTPUT using one as a sink one as a(n analog) source and then reverse to get the needle to the other side of center? Obviously it would need a resistor in series to reduce the current down to some reasonable level so it doesn't go off-scale. Is there a better way to control the meter?

can I just hook to 2 PWM pins, set both to OUTPUT using one as a sink one as a(n analog) source and then reverse to get the needle to the other side of center?

No I don't think that would work because the PWM outputs would act as both a source and sink depending on the logic level at the time. If you first smoothed the PWM signals then you could attach one to each end of the meter. Then it would show the difference between the two, that would go both sides of center.

Presuming the underlying measurement scale for the 0-1000 is 0-1000uA

How did you come to that conclusion? I couldn't see anything that would support that.

No I don't think that would work because the PWM outputs would act as both a source and sink depending on the logic level at the time. If you first smoothed the PWM signals then you could attach one to each end of the meter. Then it would show the difference between the two, that would go both sides of center.

Riiiiight. Didn't think of that. What's the simplest way then to smooth those signals? Still in the learning stages of this hardware stuff: would a simple low-pass RC filter work? Or is there some better way to control the meter?

How did you come to that conclusion? I couldn't see anything that would support that.

Sorry, that should have read "I've grabbed" not "I've got" as they've not yet arrived :P - I actually don't have anything to support that - 0-100uA is the default scale on the 0-100 meters I believe from reading the item description so I presumed 0-1000 scale was 0-1000uA. Might be completely wrong as I don't have them yet.

Well you might try controlling it with a single PWM output signal. The meter will have + and - terminal, so on the - terminal wire it to a fixed +2.5vdc voltage source (resistor divider, voltage regulator, voltage reference chip, etc). Wire the + terminal to a series resistor of correct value and the other end of the resistor to a PWM output pin. So max PWM output should drive meter to max positive scale and min PWM should drive meter to min negative scale. And of course a 50% PWM output should center the meter.

At least that is my first stab at it. Not sure if the meter will be dampened enough to be effected by the PWM switching frequency or not.

Lefty

Thanks, Retro, a simple resistor divider off the +5V to provide a ~2.5V - terminal voltage works beautifully - these meters seem to be unaffected at the ~500hz PWM output from the Nano. XD

Zenzizenzizenzic: Thanks, Retro, a simple resistor divider off the +5V to provide a ~2.5V - terminal voltage works beautifully - these meters seem to be unaffected at the ~500hz PWM output from the Nano. XD

Great, and so you now have a pretty simple and unique user feedback device to put to whatever use you wish. That should prove that it's pretty simple to utilize most basic DC meter movements into an arduino project with minimum difficulty. Most DC meter movements are of a basic 0-1ma movement regardless of their scale markings, although there are 0-100ua and 0-50ua meter movements somewhat common also. Most are not of the center zero type so won't require a 2.5vdc 'bias' applied to the negative terminal, just an appropriate size series resistor to a PWM pin.

Lefty

Zenzizenzizenzic: Thanks, Retro, a simple resistor divider off the +5V to provide a ~2.5V - terminal voltage works beautifully - these meters seem to be unaffected at the ~500hz PWM output from the Nano. XD

I am not surprise, even needle able move that fast ( it not). The eye would not.

my best shot;- use 4066 analog switch with Arduino 2 analog pins via resistors to meter terminals and 2 digital pins to 4066 control which meter terminals to ground.

my best shot;- use 4066 analog switch with Arduino 2 analog pins

Why when one PWM pin and two resistors work?

Grumpy_Mike:

my best shot;- use 4066 analog switch with Arduino 2 analog pins

Why when one PWM pin and two resistors work?

Three resistors, two for the voltage divider and one for the pwm output series current limiting resistor.

Grumpy_Mike:

my best shot;- use 4066 analog switch with Arduino 2 analog pins

Why when one PWM pin and two resistors work?

output range,

mine: +/- 5.00V

one PWM pin and two resistors work: +/- 2.50V

retrolefty:

Grumpy_Mike:

my best shot;- use 4066 analog switch with Arduino 2 analog pins

Why when one PWM pin and two resistors work?

Three resistors, two for the voltage divider and one for the pwm output series current limiting resistor.

Ok, plan B: Three resistors, two for the voltage divider and one for the analog output series current limiting resistor.

You only need two resistors. The PWM output current is limited by these potential dividers as well. If you only have a 5V meter unlike the OP then you will have to use two PWM pins and no resistors.

Grumpy_Mike: You only need two resistors. The PWM output current is limited by these potential dividers as well.

Are you sure?

Yes.