UNO as a 1mA Analog meter driver replacing an op-amp.

Hello,

What I am trying to do is compare to input voltages. 1 is the reference voltage say 3volts. The other is the “signal” anywhere from 2.5 to 3.5 volts. The greater the difference the higher the output voltage proportional to the difference. The current needed to fully deflect this meter is 1mA through its 50ohm load. That is a complete range of output between 0mV and 50mV. I believe that with these values the UNO would not be damaged.

I have read that the AD /DA converter has 1024 divisions over 5V (5000mV) or 4.88mV per division. I believe this is enough resolution to operate in an similar fashion as the analog op-amp driven panel meter.

Is this a reasonable project for the Arduino?
Does the Arduino UNO offer negative output voltage?

This is just the core most basic function of this circuit. If I can get this to work then I can add features easily by manipulating digital values. I.E. if the difference in Vref and Vsig is 20 units turn a warning led on.

Please know than I am only stating how I think this may work and am looking for guidance on how it may actually work. :smiley:

For the electronics knowledgeable I have attached a pic of the circuit. U4 represents the physical analog meter. R1 and R2 are the legs of a piezo resistiv voltage divider that creates Vsig depending on pressure (strain gauge.)

Jeremy

Is this a reasonable project for the Arduino?

I can't see what you gain.

Does the Arduino UNO offer negative output voltage?

No.

jgaupel:
Does the Arduino UNO offer negative output voltage?

No, but you can drive an analogue meter between two output pins (at least one has to be a PWM pin), as an h-bridge.
That will deflect the meter positive and negative.
A 1mA/50ohm meter would need a 4k7 resistor in series with the meter, and a ~10-100uF (bipolar) smoothing cap across the meter.
Leo..

Grumpy Mike,

The gain I would accomplish is in the fine tuning that would be alleviated by using the Arduino. The analog circuit has 10 turn 50ohm potentiometer with 10ohm resisters in parallel on each segment, each segment is in series with a 500ohm potentiometer and a 1Kohm resister.All this is just to zero the meter. :frowning: I am thinking that I can put some code in to compare the Vref and Vsig at “idle,” tell the arduino to make that zero, and simply use that offset in my calculations.
Also if I want to set an alarm its just a mater of deciding at what output value corresponds to the alarm set point I want and throwing an unused pin HIGH.
At least that is what I am hoping.

Jeremy

The analog circuit has 10 turn 50ohm potentiometer

And you think that the 10 bit resolution of the internal A/D gets you anywhere close to a 10 turn pot on the input side? And the 8 bit resolution for PWM gets you anywhere close to the resolution you need on the output?

G Mike

That is why I went into some detail about what I was doing. I was hoping to get some feedback. The question is not "can I get infinite resolution with arduino's DA /AD" IT is "will arduino fit my needs for a reasonable analog meter drive over the range of my Vref to Vsig difference?" The beauty of the analog meter with a custom face is that the meter is slow and the actual current running through the "coil" is meaningless to the end user in my case. This meter is a visual tool for an operator to know how hard they are pressing on a gem stone facet. That is why the Vsig comes out of a strain gauge.

Jeremy

will arduino fit my needs for a reasonable analog meter drive over the range of my Vref to Vsig difference?"

This is hard to say as you have not put figures on what you consider reasonable.