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A wearable sound-to-light display, without a microprocessor - the Musicator Junior.

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Picture of A wearable sound-to-light display, without a microprocessor - the Musicator Junior.
MJr03a.jpg
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

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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

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.
 
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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)  theWobblebot15 days ago

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_n10 months ago
Has anyone done this on a breadboard? If so, is there maybe a reference photo anyone could share? Thank you!
ThatABoyce2 years ago
Is it possible to use RGB LEDs? Would you need to redo the whole thing.
qs (author)  ThatABoyce2 years ago
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.
dlane42 years ago
could the microphone be wired to be away from the unit itself?
qs (author)  dlane42 years ago
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.
Goodbuddy322 years ago
Could this be used with el wire instead?
qs (author)  Goodbuddy322 years ago
EL wire requires over 100-volts to work, so this circuit cannot work with it without major changes.
EET19822 years ago
As soon as my LM358's come in I'm going to build this :). Cool project. Thank you.
qs (author)  EET19822 years ago
You're very welcome. Enjoy!
BrysonReece2 years ago
Would the NTE975 Op-Amp work instead of the LM358? The local Radioshack only carries the NTE975.
qs (author)  BrysonReece2 years ago
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.
umfan1102 years ago
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


thanks
qs (author)  umfan1102 years ago
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-Five5 years ago
Here's one that I drew.
123.bmp
Jim5975 J-Five5 years ago
can you label r1, r2, c1 etc......
J-Five Jim59754 years ago
what do you mean?
Jim5975 J-Five4 years ago
r1= ???ohms etc
J-Five Jim59754 years ago
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 J-Five4 years ago
ok thanks

J-Five Jim59752 years ago
No problem.
Awesome Instructable..i have done something like this using Arduino and Processing!
But this one is real portable!
Im making this one...
Cheers!
qs (author)  indiantinker2 years ago
Thanks! I hope you have fun building this simple project.

And check out my Arduino powered Level Display too!
umfan1102 years ago
is there any way that you can split it into high, mid, and lows
qs (author)  umfan1102 years ago
I have a couple of other projects that do that, including this one: http://www.instructables.com/id/A-Triple-Channel-Musicator-the-TriM/ and the Android driven Musicator: http://www.instructables.com/id/The-LED-Matrix-Panel-or-LMP-for-the-Arduino-micr/

Hope they're what you're looking for!
umfan110 qs2 years ago
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)  umfan1102 years ago
COM stands for Common - if Red and White are the RIght and Left channels then the Common is usually the Black wire.
musick_083 years ago
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: http://www.instructables.com/id/Music-LED-Light-Box/
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_083 years ago
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 qs3 years ago
I think this would work. i wanted a small circuit that could be used with a small battery source if needed. thanks
AronC08163 years ago
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.
thealeks3 years ago
would it be hard to use 6 mics that individually trigger 6 LED's?

thanks
qs (author)  thealeks3 years ago
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 qs3 years ago
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)  thealeks3 years ago
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.
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