Re: Voltage Scaling


<ggold6@xxxxxxxxx> wrote in message
news:f15c2198-ac09-4a15-9d2a-ce10f45a631a@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Thanks for the quick reply.. will definitely try this.

For the curious:
The project is to build something along the lines of the following
clock (i'm using arduino diecimila):

http://web.jfet.org/weston-clock/

the board gives several variable 0-5V pwm outputs, but i can't find
analog panel voltmeters for anything less than 0-15VDC (also i have a
beautiful pre-WWII -3V~3V panel one which i really want to use, which
explains the need one of the scaling circuits). If anybody knows where
i can find 0-3V (or something along those lines) analog panels, that
would save a lot of hassle..

Also, usingDS1307 RTC the proper voltage is delivered to the 3 panels
(for sec's minutes and hours display).
In the spirit of open soft/hard-ware i'll post links to circuits and
code for the whole project when it's done..

Thanks again, gilad.

Analog voltmeters usually have internal resistors to provide scaling. You
should be able to open up the meter and change the resistor so the 0-15V
meter becomes 0-3 VDC or 0-5 VDC which can be driven directly from the PIC
PWM.

If you can connect the (-3V)-0-(+3V) meter to a bridge type circuit, you
can drive it without a negative supply rail. Or even directly between two
PWM outputs of the PIC.

It may also be possible to rotate the rear spring adjuster of the meter far
enough to make the pointer rest at the leftmost mark on the scale. Long ago
I worked as a meter technician and we would modify analog meters for
suppressed zero, live zero, and center zero. But these were more modern
meters, vintage 1975 or so, and not 1894 or 1940s. I'm not *that* old!

You can also look for switchboard DC ammeters, which are generally 50 mV or
100 mV full scale. They usually take a little more current to drive, but
probably 10 mA or less, and you can just add a series resistor. Or look for
0-1 mADC and add a scaling resistor (1000 ohms per volt).

If you'd like to make an analog display with a full 360 degree display, you
could use a "synchroscope", which measures the phase angle between two AC
voltages. See http://en.wikipedia.org/wiki/Synchroscope

Paul


.

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