Led - VU Meter




About: I'm an amature engineer, love to build things that use lights, lasers, LED's.. you name it. Other from that, i run a Photography business, and i L0V3 taking pics :D
In this instructable, I will show you how to put together an analog VU-meter.
You can plug any light in (with the right voltage ofc) and it will work.

A Vu-Meter is simply measuring the volume of the sound, the bigger the voltages, the higher the light will go on the bar. :)
Though, getting it accurate takes calibrating and such, and I will not go over that.

This is as simple as it gets, and it's pretty awesome!

Step 1: Gather Your Parts!

The main component we are using this time is the "Tip 31C"
Standard transistor, cheap and easy to find.
How many?
Use as many as you want!

Then you need just as many diodes + a few spares. (take note of the Vf drop they have, too high, and you can't use many leds with low voltage)

A pcb board.

a pin-breakable thing :^) -- The same thing you use to build shields with.

A potentiometer (100k for this one) To adjust sensitivity on the bar.


A simple switch.

Some Led's 

And last but most important, a lunchbox.

Step 2: Step 1, or Step by Step, or Step, or ..

First of all, you want to put the transistors in a nice line to work with, not to close, and not too far away. (I calculated the holes exactly)

Then you solder a Diode (shown on the picture) as a starting rectifier for the BASE-pins.
Connecting another diode onto the end, with another diode, and so on. so you "split the voltages, the further away you go.

Since there is a Forward-voltage, you drop, in this case 0,6V per diode. Making the LED's shine less the further away it is in the bar.

Continue adding a diode, then connecting the end to a base with a resistor (10k ohm)
(view the picture)

Trying to view from below just makes my eyes hurt.

Step 3: Connectors

Moving on with adding some metal pins so we can easily connect our LED's to the board.

And not necessary, but done here, a simple passive low-pass filter done with a 1k ohm resistor and a 1µf capacitator.
(sorry for poor documentation here)

Step 4: Testing the Shizzle!

Hook it up to a few led's to see if it runs as it's supposed to do.

And connect the speakerwires to the base-pin and ground to make it show you how loud it is!
Adjust with the potentiometer if you are playing really loud.

Try the low-passfilter to see it bounce to the base-line and beat. Really eyecatching.

Step 5: Lunchtime.

Bring out your box, or in this case, the lunchbox.

Start punching holes in it, calculate where you want your switches to be and so on.

Step 6: Soldering and Soldering!

Okay, you made it this far.

So start adding on those LED's.
Remember to get them in the correct order.
The first transistor shines the most, the next one, a bit less, next one after that, more less, etc.

Solder the grounds to the pins of the transistors and the positive (to the positive of your power source, ofcourse)

Step 7: Add Some Glue and You Are Done!

There you go!

Hook it up to your stereo and watch it bounce.

I added some extra pictures to make it a bit easier with the electrical wiring.

If you are watching the third picture.

The bottom right 2 pins are the sound-input.
Top pin is positive, and bottom one is negative.

The top left 2 pins are for power supply (12V or depending on the LED's)
Left one is positive, right one is negative.
The left one is connected to all the LED's

IF you have any questions, be sure to comment or send me a pm!
It could be a bit confusing perhaps, since i messed up with some pictures :^)



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    42 Discussions


    4 years ago

    I guess I see that you said a leg of the resistor connects to the diode.. and in the schematic it then shows the other end of the resistor connecting to a leg of the transistor.. In the schematic I think it shows the other end of the resistor connecting to the center pin of the transistor but from the bottom side of your pcb board the soldering u did doesn't look like the resistor connects to the center pin?? Sorry I am electronic illiterate.

    1 reply

    Reply 4 years ago on Introduction

    The audiosignal which goes up and down in voltage when the music plays, is the line the furthest to the left with the AC-symbol. If you follow that line, you will se intersections of the other lines (cables)
    However, the lines that cross over and have a dot at the crossing, means that they are soldered together.
    If there aren't any dot at the intersection, the lines go over or under eachother.
    If that's what you meant.

    And the schematic is always a simplified version to make it easier for people to view and understand it on paper. when you have it in your hands, the pins could be swapped, and you have to check which one is the base, the emitter and source.


    4 years ago

    Can you please help me with the basics of this circuit?? How does the resistor and diode connect to the transistor?? How is that circuit built. ?? And what specific diode do I need to by?? Is it used as a switching diode?? I'm not the smartest about this at all.. But any help would be appreciated! !! Thank you

    2 replies

    Schematics don't necessarily show the pins in order. You have to look up the datasheet for the part to find out which pin is which. B connects to the resistor/C to the LEDs/ E to ground. I would guess that he is using something like a 1n914 diode. When a diode conducts it has a voltage loss across it (for the 914 it is .7v). Here that is used to "chop up" the audio signal level & use it to turn on the transistors in order. Hope this helps!! Cheers!

    DufvaLectric Wizard

    Reply 4 years ago on Introduction

    1n4148 - Diode actually, but you weren't too far off!

    And yes, the diodes is used to create a voltagedrop the further "up" the chart it goes.

    The schematic is correct, but when you come to real-life soldering you might have to do some adjustments because the pins could be in another order as "Lectric Wizard" wrote. :)

    You should correct your schematic to show where the diodes go. Technically what you have created is a "color organ" not a Vu meter. A Vu meter is a logarithmic meter used to measure audio levels, it will react very differently that this. None the less great job building it & on the instructable !!

    4 replies
    DufvaLectric Wizard

    Reply 5 years ago on Introduction

    Well, I did my research and I wouldn't call it a color organ completely, since the higher the volume the further up the LEDs it shines.
    And yes I need to update that schematic,, missing original file though :(


    Reply 5 years ago on Introduction

    Let me know when you update your schematic, and I will feature your project :D

    Community Manager


    Reply 4 years ago on Introduction

    I am wanting to build this thing but don't know much about electronics at all.. Can you help me out with this?? It seems like you ran the center pin of the transistors to run to the negative pin of your led strip... however the schematic seems to show the center pin going to that resistor and then to the diode string?? I don't understand?


    5 years ago on Introduction

    Awesome project!! Quick question, what kind of LED strip is that and where can I find them? Thanks so much!

    1 reply

    5 years ago on Introduction

    it will be nice if I could now the right position of potentiometer in wiring shema...I bought the whole PDF, so....

    3 replies

    Reply 5 years ago on Introduction

    The potentiometer is positioned on the line in.
    The sound input that is :-)


    5 years ago

    Would you be able to have the sound be determined by a 1/4" input for a musical instrument with a 1/4"output as well? Basically I want my guitar to control the LEDs but still output to my amplifier for live shows. Could you build this? I'd pay ya for it! :-)


    5 years ago on Introduction

    Just looking, your strip LED's that you're using are multi coloured, so you could set it up so that the bottom few are green then yellow, then red. Would look more like a VU meter then. :)

    2 replies

    Reply 5 years ago on Introduction

    That's correct :)
    But i didn't have any coloured led's when i built it, and fully red made it look sweet aswell.