[sdiy] How to measure VU meter properties

René Schmitz synth at schmitzbits.de
Sun Oct 19 12:33:03 CEST 2014


Hi David,

Am 18.10.2014 06:25, schrieb David Ingebretsen:
> How can I measure the electrical properties of an "unknown" VU meter (and
> its light) for circuit design so I don't damage the meter?

I'd use a variable power supply, and a series resistor to limit the 
current, while monitoring the current with the DVM. Then slowly ramping 
up the voltage from 0 to 15V (or whatever).

Most meters have full-scale currents in the range of 50u to 500uA, so 
100k series resistor would do as a starting value, making it smaller if 
we can't hit the end of the scale.

Check the lights for continuity first, chances are the lamps are broken. 
If so I'd consider replacing them with warm-white LEDs.

Other than that you can only guess the voltage, by carefully ramping up 
voltage and judging by the color of the light, stay on the 
yellow-reddish side. Lamps last much longer with undervoltage, which is 
usually the way these lamps are operated. E.g. 7V scale lamps were 
typically run on 6V.

Cheers,
  René

-- 
synth at schmitzbits.de
http://www.schmitzbits.de/



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