Re: Building DC Voltmeter


"vwq47"

I'm wanting to built a DC volmeter from a moving coil ammeter. I have all
the info and can calculate the series resitstor I need to make a (say)
1-20V meter. It's an automotive use. What I would like to do do is
offset the zero so the zero reading is say 8V and the maximum 18V. I
can't for the life of me find a simple circuit that will work, though I
knowq I have seen them, using a regulator. Can anyone point me in the
right direction please?



** Just make the volt meter and series resistor up so it reads 10 volts
DC, full scale.

Then fit 8 volt " amplified zener " in series with the lot.

This consists of an NPN transistor ( ie BC 548 ) with a small ( 400mW ) 7.5
volt zener wired from collector to base and a resistor of about 1 kohms from
base to emitter.

The transistor's C-E terminals now make a sharp, low leakage 8.0 volt zener
with C the anode end.




........ Phil





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