using analog audio VU meters?

[dentaku]

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?

[Paul Price]

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.

[Richard Crowley]

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.

[dentaku]

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 something
I 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.

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.

[Richard Crowley]

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 circuit
There 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?

[katzohki]

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 circuit
There 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?

Or: "What's cheap and will do the job?"

[dentaku]

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 circuit
There 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?

Or: "What's cheap and will do the job?"

I 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 CAN
Now 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.