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
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
Try Googling "expanded scale voltmeter".
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.
"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
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
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