USB-powered Musicator




Introduction: USB-powered Musicator

This is a very simple Musicator that runs off the USB port. In its basic form, it only uses 4 components plus a single white LED. The 'star' of the show is the LM431 'Programmable Zener Diode' - which costs under 20c, so our project can be made for about a dollar in parts!

This allows us to double it up and have separate Left and Right channels, as shown here and below.

Step 1: Some Sample Videos

As you can see, the circuit is very sensitive and is able to display even soft passages on low listening volumes.

Step 2: What's Needed

The parts:

LM431 Programmable Zener
15K resistor
120-ohm resistor
1uF capacitor

You will also need a means to plug into the earphone socket of your music player and a male-"A" USB plug.

You can perhaps see an earlier prototype in the rear of the image below. There I've modified a perf board as a USB plug. It works, but definitely is not recommended unless you know what is involved and you have an inexpensive USB port to test on.

Step 3: How Does It Work?

How do we get a Zener diode to play music you may ask. The answer is the unique circuit inside the LM431. Within its transistor-like package, it packs a comparator and a precision voltage reference of2.5v, which is useful here, because it is exactly mid-way of our USB supply.

We are using this precise voltage to bias the LED just below its Vf, in fact you will see a faint glow even with no signal.

The input pin is monitored by the 'reference' pin and any changes in the signal shows up as fluctuations in our LED. The 15K resistor controls the sensitivity and can be as low as 3.3K if you like your music loud, or if your phones are less efficient. The LED brightness is controlled by the 120-ohm resistor.

Step 4: Assembly

With a handful of parts, the circuit is simple to assemble.

The images below should help you arrange the parts.

Note: You should not space the LEDs more than 3/4" (18mm) apart, otherwise your eyes will not detect out-of-phase signals used for surround sound effects.

See more of my circuits here.

Step 5: Variations

The LM431 is truly quite impressive. Here in a variation of our circuit, we have it driving a 1/2-W LED, not only that, it is also powering a little speaker at the same time!

Step 6: Variations 2

WIth some minor changes, our circuit can be adapted to other voltages. Because all the LEDs are in series, they can all be controlled by the LM431 by monitoring the last LED in the chain.

Basic calculations:
E = 0.9 * (V-1)
e = 3 for White, Blue, Pink, Violet or Green
e = 2 for Red, Orange, Yellow or Yellow-Green
Subtract e of each LED from E until it is close to 0. This is the most efficient combination for a given supply voltage.

R1 = 50 - 100 ohms (Brightness)
R2 = 10k - 47k-ohm (Sensitivity)
C = 0.5 - 1uF. Positive side towards TL431. Connect the Negative side to either the tip (Left Channel) or the first Ring (Right) of a Stereo plug.

Step 7: Variations 3

With a small sacrifice in sensitivity, we can substitute an NPN transistor for the LM431. Use the same process as above to calcuate LEDs supported.

Choose an audio-frequency transistor with a high beta (gain) of 150 or more. 2N4401, BC337 are good choices. Also acceptable are 2N2222 and 2N3906. Otherwise, check the datasheet for a device that:

is NPN
has a gain (beta) of 150-500
can handle 500mW or more
can handle 150mA or more
Voltage 50% higher than the Supply

R1 = 50-100ohm (Bright)
R2 = 100k - 390k (Sensitivity)
C = 0.1 to 1 uF. Negative side to music output.

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    18 Discussions

    Im confused on the schematic. Where does the usb come into play? where does the input from a music source go?

    Sorry, i am a beginner in electronics.

    P.S. Really cool instructable! i am excited to learn how to build it!

    1 reply

    The music comes from the earphone plug of a player or laptop - see Step 6 for an idea of how they are connected.

    Great Instructable! Only one problem, I built this exactly and it works great, but how can I get the lights to flash with a heavy bass beat instead of with most vocals? Right now the lights hardly flash with the beat like they do in transistor based music light effect generators. Any ideas?

    2 replies

    You can modify the frequency response of this circuit by adding a ceramic (or disk) capacitor in PARALLEL with R1, the 15k resistor. The capacitor can range anywhere from 0.001uF (1nF [102]) for reduced reaction to higher notes; all the way to 0.05uF (50nF [503]) to allow only Bass notes.

    Thanks! Another thing that worked for me was to add a resistor capacitor low pass filter to the input, I'll try this though now.

    2 questoins. what did u make those tubes out of? and if i used a Tip31c, would that act the same as a LM431?

    4 replies

    The tubes are white drinking straw cut to 1" (2-3cm) lengths and crimped at one end after heating/melting.

    The TIP series of transitors are low-gain trainsistors meant for switching 5 or more amps - and is NOT suitable for these applications, which requires the sensitivity to control less 1/30th of an amp.
       Despite its simple appearances, the LM341 has a dozen transistors inside that provide the functions used here. 

    so would it b possible to replace the Tip31 with a LM341 in this diagram?


    I've added a couple of steps above to show how to use this circuit with other voltages. They will be many times more sensitive than the circuit you showed.

    Look it over - I'll be out of town for a bit but I'll answer any question when I have a chance.

    If there is enough interested, I will add more circuits for other options and larger displays.

    a LARGER scale version would be pretty cool. I've just ordered parts for some of your projects. I can't wait to get them up and running!

    Absolutely fantastic. I've just begun to dabble in micros & electronics, having received my Amateur Extra radio license at age 63. Hope I live long enough to understand and even develop projects like this. Great job = 5 * Can you identify the band in the first video?

    1 reply

    Thank you for your kind words.

    I enjoy electronics - especially the bits that shine. My job does not allow me a lot of time to build complex project so I tend to design the simplest circuits that'll do the job. Check out my website and my other projects - you'll see what I mean.

    The piece is Chantal Kreviazuk singing John Denver's "Leaving on a Jet Plane" from the Armageddon movie soundtrack. 

    Thank you.

    I'm fascinated by devices that combine Music and Lights, and this one worked out rather well.

    this is amazing :D one question though; i've build other "muzicators" but they all share the problem that when you turn up the volume, they are way 2 bright. or, on a too low volume, theyr not on at all. is it any different with that programable diode?

    2 replies

    With this design, there won't be any 'drop out' on low volumes - if you can hear it, it will display it.

    This Musicator will work until the phones get uncomfortably loud, but in extreme cases, a 1K pot can be connected across the input and ground, with the - side of the 1uF capacitor connected to the wiper.

    The accuracy of this is very high. The last video of it driving both the LED and speaker is pushing it to its limits and it still shows excellent linearity.

    k, il try that, whenever i get those programable diodes :D