using analog audio VU meters? - Page 1
Forum section: electronics / beginners

author: dentaku
author_rank: Frequent Contributor
timestamp: May 20, 2014, 08:41:44 pm
content: I salvaged two VU Meters from an ancient wooden Realistic/Radio Shack tape recorder.I has separate pots for left and right and a VU Meter for each side.How can I uses these meters to read a regular audio signal from a headphone jack?Since the needle sits at the bottom of the scale and swings up I'm assuming the audio signal has to be rectified somehow?

author: Paul Price
author_rank: Super Contributor
timestamp: May 21, 2014, 01:53:29 am
content: Rectified yes, maybe even amplified by an op-amp and also calibrated for the markings on the meter to have any revelance. May require a logarithmic drive signal.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 21, 2014, 02:09:16 am
content: It is hard to say what you need without knowing what the meters are. They are almost certainly DC current meter movements with a "VU" face. So you will need a simple circuit to create the DC current to drive the meter based on the AC audio signal. If you have a DMM, you could use a pot (like 100K) and a 1.5V battery to figure out how much current it takes to move the needle up to full-scale. Then you will know what circuit it takes to drive them.Since they have a lograthmic scale, you don't need to use a log-conversion circuit. If they had a linear VU scale, then you would need a log-conversion circuit.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 25, 2014, 03:05:34 pm
content: I know this is an old thread but I just found that someone answered.I used an AA battery and a 100K pot and it looks like these meters hit 100% at around 256uA and go off scale past the red at around 500uA.I might actually be able to use these for somethingI used the same method to test the signal strength and center tuning meters from an old Drake ESR 24 Earth Station Receiver. They're pretty much the same values as the ones from the old RS tape player.Quote from: Richard Crowley on May 21, 2014, 02:09:16 am

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 25, 2014, 08:08:55 pm
content: OK, so you have 500uA DC meter movements. Good. Most any DC meter driver should work.A Google image search returns dozens of options for: vu meter driver circuitThere are many design trade-off decisions to be made here. For example:How sophisticated do you want? What kind of power is available to supply the circuit?

author: katzohki
author_rank: Frequent Contributor
timestamp: June 25, 2014, 09:22:18 pm
content: Quote from: Richard Crowley on June 25, 2014, 08:08:55 pmOr: "What's cheap and will do the job?"

author: dentaku
author_rank: Frequent Contributor
timestamp: June 26, 2014, 12:44:00 am
content: Quote from: katzohki on June 25, 2014, 09:22:18 pmI just did some experiments with what looks like an old germanium diode to build a half-wave rectifier type of circuit and every analog meter I own (salvaged junk) reacts quite well to a mono audio signal.It cost me $0.00 CANNow I'm curious about the old scavenged Cornell-Dubilier AM Transceiver in the basement with 3 meters on it. I guess I'm going to have to test them out too.