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Sound Level Detecting Circuit


New Member
Hi guys, im new to this website
I have been given a project in a 4 credit course to design an Analogue Sound level detecting circuit
I was thinking of maybe the output being designed as a series of LEDs connected in parallel with resistors in each branch so that as the sound increases, a condensation mic would produce a signal which would be amplified by an OpAmp and then fed to the LEDs which light up. More LEDs means a louder detected sound.
This is my first circuit laboratory course in university and im honestly starstruck.
Can someone please help me make the circuit design on LTspice?
Any help would be appreciated!


Well-Known Member
Most Helpful Member
I'd suggest something like this:

Followed by something like this:

The preamp brings the mic signal up to a reasonable level, then the VU meter circuit rectifies the audio and feeds it to the comparator inputs, which switch the appropriate LEDs depending on level.

I would also replace the simple diode rec at the input of the VU circuit with an active rectifier, something like this:

You could use an NE5532 dual audio opamp for both the preamp and rectifier.

You will need to adapt some things and adjust gains, bias circuits, the levels of the comparators etc. - but that's where you need to start experimenting and calculating.

(It's not reasonable for someone else to do the whole project for you; help and advise is a different thing, as long as you put a reasonable effort in to it.)


Well-Known Member
Most Helpful Member
Sound levels and our hearing are logarithmic like an obsolete LM3915. An LM3914 is still made but it makes a linear voltmeter, it is not logarithmic.
I designed and made my Sound Level Indicator project 14 years ago and it has been working day and night nonstop. It uses an LM3915, a dual opamp and 3 transistors.

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