# Building DC Voltmeter

Discussion in 'Electronic Basics' started by vwq47, Jul 27, 2007.

1. ### vwq47Guest

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?

Thanks

dave

2. ### Tom BiasiGuest

You are already going in the right direction.
You have the range that you want but want to start at 8V. Cheap and dirty
way is to insert an 8 V, zener in series with your resistance.
The meter won't start to read until 8V. and the readings will be 8V. less
than actual. This is not real accurate and you will lose some linearity, but
for automobile use you probably won't notice.

Tom

3. ### MikeGuest

Try Googling "expanded scale voltmeter".

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/2/02pg31a.gif for a
schematic and http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/2/02pg31.txt
for a text explanation of the circuit.

The 723 could be replaced by a TL431 shunt regulator or even a zener diode.

Mike

When truth is absent politics will fill the gap.

4. ### Phil AllisonGuest

"vwq47"

** 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

5. ### vwq47Guest

Thanks all - Tom , Mike and Phil . . . these are helpful suggesions. I also
happened on a SC circuit of ?1995 with two 5V regulators, republished last
year some time.
I have lots to go on now.
Thanks again - for the time and care!
Dave

6. ### neon

1,325
0
Oct 21, 2006
you have been fed missinformation. the amp meter or whatever it says is probably an microampere meter or milliamperer meter the movement to full scale is around that. you must find out before anything else. otherwise blewwwwe. once you find the current neccessary for full scale deflection then the the inplementation is easy if it is a 50 uamps then to read ful scale you need to supply 50uamps to the meter for full scale deflection and that is ohms law..