I don't know if the ADC pins are accurate enough to make a meter 
based on a microcontroller alone.  That said, I know there are some 
very nice ADC chips out there that would integrate trivially with any 
microcontroller, have fast conversions, and microvolt accuracies.

It could be done.  And perhaps it should be done.  There's nothing 
very magical about the parts of either a VOM or a DMM.  The most 
complex bit is usually the big gang switch that tends to be used 
mostly as a cost-saving measure.

It could be done.

Joseph - KF7QZC


On Fri, Oct 14, 2011 at 12:03:30PM -0500, Martin McCormick wrote:
>	I am surprised that nobody has come up with a talking
>VOM that could also give an analog style indication. What I am
>thinking of is a talking multimeter that gives you the numerical
>values that one needs as well as a tone that rises and falls
>with the readings. It wouldn't be that difficult especially with
>digital circuitry. One could listen to the tone and get a rapid
>indication if some value was rising or falling and then push a
>button or whatever to call for a quantitative readout.
>
>	Another way to do that is with a VCO or Voltage
>Controlled Oscillator. There are several VCO IC's out there but
>one would want one with a large range so that you could hear
>small changes more easily. It would have to be just in front of
>the analog-to-digital converter circuitry so that it would work
>on all ranges.
>
>	Most of the analog-to-digital converters I have studied
>work on a 0 to 5-volt range. One extreme gives you the maximum
>output number as in all ones and the other extreme gives you all
>zeros.
>
>	Some of the PIC microcontrollers have A/D converters
>with a 1024-bit resolution which could make for a pretty good
>meter as long as it stays accurate.
>
>Martin McCormick WB5AGZ  Stillwater, OK
>Systems Engineer
>OSU Information Technology Department Telecommunications Services Group