[sdiy] +/- 15V voltmeter

[tomg@efm]

> Excellent!

Even better add another 50K pot (no resistor needed) and a 
spdt. Adjust the SSV which should really be a ZCV( zero x-ing 
vm ) or even ZCDCVM  ( zero x-ing DC vm ..;-) so that 
.5 = 1V and you have a dual range +/-16V (full range) +/-4V 
vm.....much more useful.....;-)

The (-) terminal should actually be labeled gnd and the (+) terminal
should really be labeled (+/- V ).....and you should really drop
a nice bright blue led in behind the scale....;-)

Tom