Introduction: A Wearable Sound-to-light Display, Without a Microprocessor - the Musicator Junior.

Picture of A Wearable Sound-to-light Display, Without a Microprocessor - the Musicator Junior.

Smaller than the 9-volt battery that powers it, the Musicator Jr. displays the sound it 'hears' (through the Electret Microphone) as fluctuating light bars.

Small enough to fit in your shirt pocket, it can also be placed on a flat surface to monitor the sound levels around it.

An alkaline battery will easily power it 20 or more hours.

Step 1: The Parts Needed

Picture of The Parts Needed

The 'brains' of this project is a LM358 general-purpose op-amp which costs under 30-cents. The first half of the circuit is an amplifier which boosts the 500-micro-volts from an electret mic to about 1-volt. This level is generally called 'Line-level' and can be used to drive our LEDs, an audio amp, or even the input pins of an Arduino processor.

The second half of the op-amp is used as a voltage-to-current converter, which limits the brightness of the LEDs to 10mA or less.

The complete list of parts is below:

LEDs. Any combination can be used, as long as their total forward voltages is less then 8. For example, you can have up to 4 amber LEDs with 1.8v Vf.

Electret microphone - I got mine on eBay for under 25-cent
LM358 - Op-amp (8-pin DIP). Also available on eBay.
2N4401 - NPN general transistor (other audio NPN-types will probably work as well)
10k resistor x 5
2.2k resistor x 1
470k resistor x 1 (Can also be 330k as labeled in the circuit)
100-ohm resistor x 1
1uF capacitor
0.1uF capacitor
9-volt battery and connector
Perf-board and mounting parts.

Total cost: $3 or less.

Step 2: The Schematic

Picture of The Schematic

Thanks to echoskope for this schematic!

You can download a larger copy of the circuit here.

You can download a copy in pdf format here.

Step 3: Assembly

Picture of Assembly

Construction is very straightforward -the only caution is the electret mic is polarized - the side which is connected to the outer casing is Ground (or Negative). See the last image for the pin-out of the one I used - note the connections to the shell from the - pin.

The first image is the completed board from both sides, followed by an 'X-Ray' image from the solder side.

Step 4: Fire It Up!

Picture of Fire It Up!
Once it's tested and working, you'll find that it's a real conversation piece at your next party or dance.

You can slip it inside a shirt pocket with the perfboard on the outside. The mic will pick up the sound from around you and the LEDs will 'perform' to it.

A final touch - cut short pieces of a clear or translucent drinking straw to fit over the tops of the LEDs. This will spread the light to give you the 'bar of light' effect.

The last image is my test rig for this project.

A video of the Junior Musicator in action here.

Step 5: Adding More Lights (and the Maths)

Picture of Adding More Lights (and the Maths)

To allow the output transistor to handle more LEDs, start by making sure you have maximum LEDs on each 'string' (ones in series): If your supply is V, then substract 2 and multiply by 0.9 Then, for each White, Blue, Pink or Violet LED, subtract 3; for others (Red, Yellow, Orange, Green) subtract 2, until you get as close to 0 as you can. This is the combination that gives you the most LED for the lowest power wastage.

Each 2N4401 (or BC337) can handle up to 8 'strings' - but you will have to make sure each string is composed of identical LEDs as the first string - then adjust R-bright to 100/n, where n is the number of strings, connected in parallel. The value of R should be 100 * R-bright.

  If you have a 9v system, then Start with (V-2)*0.9 = 6.3; Which means we can have 2 Whites OR 3 Reds, And if we have 4 strings of this, then R-bright would be 100/4, or 25-ohms. You can use 22-ohms here, and R should be 22*100, or 2.2k. NOTE: You can have up to 8 string ONLY with the 2 transistors specified. While high-powered devices like the TIP-series will work, they may not have the gain to drive the LEDs fully. If you want to use 2N2222, 2N3906 or similar audio transistors, limit the strings to 4 or less.

 One final expansion is to duplicate the entire stage, starting with R, R-bright and the driver Transistor along with the SAME LED arrangement. Connect like the previous Stage, EXCEPT, do not connect R-bright to the input of the op-amp. It is still required but only to make the load identical to the first stage. This way, you can have up to 5 stages in total.

And, if you haven't yet, check out the Next generation of the Musicator! Please vote if you want to see more of the same.


BojanS8 (author)2016-05-14

Can i use any other microphone, like a very good one so the device registers sounds from far away (5m) ?

qs (author)BojanS82016-05-14

Unless you are thinking of directional mikes (parabolic etc.) Whatever sound closest to the mike will drown out anything further away.

What are you planning to use this for?

kedarisetti (author)2016-04-23

How can u test whether a mic is working or not

EvanF5 (author)2015-01-24

I'm thinking about using an LED strip for this. Can I use more than 3 LEDs on this circuit?

EvanF5 (author)EvanF52015-01-24

Never mind, dumb question answer in directions.

theWobblebot (author)2014-10-07

How can I modify this design so that instead of the output going to the LED's, the output goes into an inverter for EL wire?
Would I just need to take out the LED's and replace them with the anode and cathode of the 9V driver?

Also, in an unrelated note, why are there only two LEDs in the schematic?

qs (author)theWobblebot2014-10-07

The circuit is current-driven, so it'll probably not suit the inverter that well. However, if you know (or measure) the minimum (dark) and maximum (bright) current requirements of your specific EL driver, you can find some work-arounds to possibly make it work.

The circuit can only drive 2 white or blue LEDs, but can do 3 red or orange ones.

miss_n (author)2013-12-15

Has anyone done this on a breadboard? If so, is there maybe a reference photo anyone could share? Thank you!

ThatABoyce (author)2012-10-03

Is it possible to use RGB LEDs? Would you need to redo the whole thing.

qs (author)ThatABoyce2012-10-04

You can use any combination of different LEDs by using the calculations in Step 5, however ...

If you mean powering the R, G and B LEDs separately, based perhaps on frequency, then see my response to umfan10, a bit further down ...

BUT, if you mean using LEDs that have all the RGB elements built in, then it's not a good idea - their close proximity gives a muddy-green effect. Not pretty at all.

dlane4 (author)2012-08-23

could the microphone be wired to be away from the unit itself?

qs (author)dlane42012-08-25

The mic cannot be more than 2-inches away from the rest of the circuit without using a shielded cable. It is much better to wire the LEDs off the board and keep the mic and op-amp as close together as possible.

Goodbuddy32 (author)2012-08-17

Could this be used with el wire instead?

qs (author)Goodbuddy322012-08-19

EL wire requires over 100-volts to work, so this circuit cannot work with it without major changes.

EET1982 (author)2012-08-07

As soon as my LM358's come in I'm going to build this :). Cool project. Thank you.

qs (author)EET19822012-08-07

You're very welcome. Enjoy!

BrysonReece (author)2012-06-06

Would the NTE975 Op-Amp work instead of the LM358? The local Radioshack only carries the NTE975.

qs (author)BrysonReece2012-06-06

In a word, No.

The NTE part is a single op-amp designed for dual supplies and requires frequency compensation. The LM358 is effectively TWO simplified NTE975's all within the same package.

A quick search through eBay will list you a number of suppliers for the LM358 at a fraction the cost of what RS wants for the NTE.

umfan110 (author)2012-06-03

just a random question if something was at 5.26 V and i needed it to drop down to 3.4V how would i do that i know you throw on some resistors on there but they dont seem to do anything


qs (author)umfan1102012-06-02

For a single dropping resistor, you need to know the current through the circuit. If you are trying to power a single, 5mm LED, for example, then the current would be 20mA, or 0.02A. The resistance you will need will then be: (5.26-3.4) / 0.02, or 93-ohms, which you can round up to 100-ohms.

The resistor should be placed with one end on the + of the power source and the other end to the + (longer lead) of the LED.

J-Five (author)2009-08-23

Here's one that I drew.

Jim5975 (author)J-Five2009-09-29

can you label r1, r2, c1 etc......

J-Five (author)Jim59752009-11-13

what do you mean?

Jim5975 (author)J-Five2009-11-14

r1= ???ohms etc

J-Five (author)Jim59752009-11-15

Sorry about that I misunderstood what you meant. Here it is

IC1 = LM358 - Op amp (8-pin DIP)
Q1 = 2N4401 - NPN general transistor
R1 to R5 = 10K
R6 = 2.2K
R7 = 470K
R8 = 100 Ohms
C1 = 1 μF ceramic disc capacitor
C2 = 0.1 μF ceramic disc capacitor

Jim5975 (author)J-Five2009-11-16

ok thanks

J-Five (author)Jim59752012-05-20

No problem.

indiantinker (author)2012-05-18

Awesome Instructable..i have done something like this using Arduino and Processing!
But this one is real portable!
Im making this one...

qs (author)indiantinker2012-05-18

Thanks! I hope you have fun building this simple project.

And check out my Arduino powered Level Display too!

umfan110 (author)2012-03-24

is there any way that you can split it into high, mid, and lows

qs (author)umfan1102012-03-26

I have a couple of other projects that do that, including this one: and the Android driven Musicator:

Hope they're what you're looking for!

umfan110 (author)qs2012-03-26

This was exactly what i was looking for did you hook this up to a mic or to a 1/8 audio jack. Mine my iggnorance but what dose COM mean i never understood that i know there is left and right but com?

qs (author)umfan1102012-03-26

COM stands for Common - if Red and White are the RIght and Left channels then the Common is usually the Black wire.

musick_08 (author)2011-05-10

instead of a microphone, could you put on a 3.5mm jack so the lights flash to a music source?

Try checking out this one:
I honestly think the circuitry on this one looks a bit simpler, but it should work for what you are thinking of.

i've used the circuit for that on other projects, but i want one that can use a battery source for portability

i have built that circuit to run off a 9 volt battery by placing the LEDs in parallel, so its entirely portable.

Oh, I see. Well, I can't say that it would work for certain, but I've run several LED's off of 2 AA batteries with the proper resistor. I haven't used the transistor that was featured in that project before, but it shouldn't cause too much impedence, I think.

qs (author)musick_082011-05-16

Check out my other circuit which uses only a handful of parts and takes the output from an Earphone plug to flash an LED. It was designed to use a USB supply, but any 4.5-6 volt supply will also work.

Circuits that only use a single transistor suffer from 2 major problems: they do not work unless the volume is cranked way up, and they distort and may even damage the sound source.

musick_08 (author)qs2011-05-16

I think this would work. i wanted a small circuit that could be used with a small battery source if needed. thanks

AronC0816 (author)2011-07-20

I have to agree with the two people above me. I can somewhat read schematics but this one confuses me. It would have made more sense if the rectangular shape of the op-amp was included and the interior circuits were shown inside that box. Then you could show each of the eight pins and what they should connect to. I tried to wire this up but it took me over an hour and it doesn't work. So apparently i did something wrong.

thealeks (author)2011-06-30

would it be hard to use 6 mics that individually trigger 6 LED's?


qs (author)thealeks2011-07-01

Nor too certain what you aim to do here - you could easily drive 6 LEDs using just the 1 mic and circuit here - why complicate things?

thealeks (author)qs2011-07-01

i want to set up a small light show for my guitar, and i want each mic to be activated by a single string, so when i play, a light will light up for each string thats played

qs (author)thealeks2011-07-02

I think you will find that, in real life, this setup will not be able to distinguish between the strings. one mic will pretty much 'hear' the same thing as its neighbor. It MAY work if you have an electric guitar and can extract the signals from each separate pickup before it goes into the pre-amp stage.

thealeks (author)qs2011-07-02

i was hopin i could lower the sensitivity, maybe by giving the mics less power, and putting the mics right up to the strings, so they only pic up their designated string. im still learning so i dont know much about this stuff, so i dont know if that will work or not

qs (author)thealeks2011-07-03

The only way to find out is to build one and see if it can be mounted to exclude sounds from other strings.

An alternate approach is to use the approach used in this circuit which splits the input into 3 distinct (low, med & high) frequency channels to indicate the pitch, rather than the string played.

thealeks (author)qs2011-07-03

i thought about that, but then the lights wont sync up with the strings, but the ideas not out.

last question, how would i change the sensitivity of the mic?

thanks for all your help, by the way, i appreciate it

qs (author)thealeks2011-07-03

The 470k resistor named "Level" controls sensitivity - the lower its value, the lower the gain. it can also be a 500k adjustable resistor so you can play with the setting that works for you.

thealeks (author)qs2011-07-09

ok awesome. thanks for your help. ill let you know how it turns out!

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