# Creating An Audio-Reactive LED Circuit

These instructions will help you learn how to construct an audio-reactive LED circuit.  Familiarity with electronics and soldering is strongly recommended  Barring any circuit errors, the task should take no more than an hour. This circuit can easily be expanded and integrated into other projects to create visually impressive effects.

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## Step 1: Safety Precautions

Caution should always be exercised when working with electric currents.  Currents can cause burns or damage to vital organs.  Currents as small as 10 mA can be damaging or even fatal.  Power sources should be disconnected when modifying a circuit, and remember to always use common sense when working with electronics.

## Step 2: Materials Needed

-9 Volt Battery (or a lab power supply)
-9 Volt Battery Connector (if using a battery)
-An Audio Splitter
-An MP3 Player (or computer)
-1 or more LEDs of any color
-1 NPN Transistor (this guide uses the 2N3904)
-1 100-400 ohm resistor
-An audio Y Cable
-A few alligator clips
-Jumper wires

## Step 3: Calculating Resistor Values

Pictured above is a chart detailing how to read a resistor value from color coding information.  The formula to calculate the resistor value needed to power a single LED is:
resistance(R) = (power supply voltage - LED voltage drop) / LED current

The typical recommended LED current is 20mA, our power supply voltage is 9V, and the LED voltage drop for a clear blue LED is 3.0V.  This results in:
(9-3)/0.020=300 ohm
Of course this doesn't need to be exact, a 330 ohm resistor will work fine here.  If we plug 330 ohm back into our formula we get
(power supply voltage - LED voltage drop) / resistance (R) = LED current
(9-3)/330 = 18 mA

18 mA is a good value to power our LED.  If the current is too low, the LED will be dimly lit, and if the current is too high, the LED will become very bright and may explode.

## Step 4: Powering the Breadboard

1) Strip off a small amount of the wire insulation from the 9V battery connector
2) Insert the wires into the respective positive and negative rails of the breadboard
-Red: Positive
-Black: Negative
tdickerson37 months ago

Would love to see the instructable for the filtered circuit also. Also the one for the newest version which has another string of LED's for the midband frequency range.

Nice work and your guides are very easy to follow.

Arijit Chatterjee8 months ago

Please upload a instructable for the above circuit. I mean for the filtered one that has different LEDs for BASS and TREBLE. It will of great help. I couldn't understand your schematic. Please ...!!!

BurgersBytes9 months ago

How did the RCA connectors get from female to male?