audio input for VU meter

TecknoTone

Joined May 20, 2012
21
There is no single input to the LM324. This chip is an op-amp array with four amps per chip. Your diagram shows eight amps and therefore two LM324 chips. The 1K resistors act as a voltage divider giving an incremental reference to each amp. If the audio level exceeds the reference level on a given amp, the LED will light.

Yes, you will need to amplify the signal from a mic in order to drive this circuit. Mics only produce microvolts and you'll need a few millivolts at least to drive his circuit. Half wave rectification and a little bit of capacitance for smoothing an DC blocking wouldn't go amiss either

This circuit is odd as everything is referenced with respect to +V rather than 0V
 

KL7AJ

Joined Nov 4, 2008
2,208
It's strange to call it a VU meter when the resistor ladder steps are all equal value instead of semilogarithmically stepped like a VU meter.

http://www.ti.com/litv/pdf/snvs762a
Alas....in recent years, many folks consider ANY kind of audio meter a VU meter. A true Bell Standard VU meter has precise logarithmic level calibration as you mention AND very specific ballistics!

This takes some care and expense to achieve....unfortunately it has fallen victim to language inflation. :)

Eric
 

TecknoTone

Joined May 20, 2012
21
What are you trying to achieve Shinigami ? Perhaps if you can set out your aims, we will be able to help you more
 
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