Sound Controlled Led Lights Circuit

In this Instructable I will show you how you can control a number of LED's with sound by means of a simple electronic circuit. You could of course use a printed circuit board for this, but as you know I like to solder the components directly together. This not only looks nice and clear, but I also find this way easier to "read" the electronic circuit and thereby understand the operation of different components!

Video tutorial:

The circuit operates on a 3 to 4,5 volt power supply. You can use 2 AA batteries, I used my power supply for this. As soon as the power is switched on, the microphone is powered. When it responds to sound, it emits an electrical signal. This signal is coupled by capacitor to the first transistor amplification. The amplified signals are sent to second transistor base. Second transistor drives LED to emit light. The louder the sound, the brighter the LED.

• 5 LED's
• 4.7 K resistor
• 10 K resistor
• 1 M resistor
• 1 uF capacitor
• 22 uF capacitor
• 2 S9014 transistors
• 3v - 4,5 volt power supply

First, let's prepare the LEDs. In my other projects I have already extensively discussed the operation of LEDs and I assume that most of you also know how an LED works. If not, take a look at my Instructables page.

• Solder all cathodes (-) together.
• Solder all anodes (+) together.

The cathode can be recognized by the length of the pin. This one is usually longer. The anode is usually shorter and the LED has a flat side on the side of the anode.

At the end of this Instructable the + of the power supply is getting connected to the anodes (+) of the LEDs, creating a + "strip". The various components used for this circuit obviously need power. To keep the project organized I start with connecting the different resistors that these components need to the + "strip".

• Start on the left side and solder the 4.7 K resistor to this
• Skip an LED and solder the 1 M resistor to it
• Skip an LED and solder the 10 K resistor to it

It does not matter how the resistors are mounted. This does not affect the operation of the resistor, it is the same in both directions.

The next step is to connect the first transistor. In the operation of the circuit this is actually the last transistor, but to make the circuit it is easier to connect this last transistor first, are you still following it?... First a bit of explanation about the operation of a transistor.

A transistor works when the electrons and the holes start moving across the two junctions between the n-type and p-type silicon. The small current that we turn on at the base makes a big current flow between the emitter and the collector. In the circuit that we are going to make, 2 transistors are used in succession. This amplifies the signal from the microphone, making it strong enough to control the LED's.

• Connect the collector of the transistor to the - of the LEDs
• Connect the base of the transistor to the 10 K resistor
• Solder the connections well

The second transistor, actually the first in the circuit, is also an s9014 transistor and of course works the same. This will therefore amplify the signal and use it to control the other transistor.

• Connect the collector of the transistor to the base of the other transistor
• Connect the base of the transistor to the 1 M resistor
• Connect the emitter of the transistor to the emitter of the other transistor
• Solder the connections well

The next step is to mount the microphone. The + side is soldered to the 4.7 K resistor and the - side is soldered to the emitters of the transistors.

Now mount the 1 uF capacitor between the + terminal of the microphone and the base of the first (remember?) transistor. Make sure you mount the + and - side of the capacitor correct. This will ensure that when the microphone is active, a signal goes to the first transistor.

If you want to know more about how a capacitor works, I can recommend you to visit the Sparkfun page. Here the operation and possibilities of capacitors are explained in detail.

Why mount a capacitor between + and -? A little explanation first: A decoupling capacitor's job is to supress high-frequency noise in power supply signals. This is why these capacitors are also called bypass caps; they can temporarily act as a power source, bypassing the power supply. Decoupling capacitors connect between the power source and ground.

• Connect the + of the 22 uF capacitor to the + "strip".
• Connect the 1 of the capacitor to the emitters of the transistors.

And the project is done! Now just connect the power supply (as shown in the diagram), turn on some nice music and the circuit works!

Video Tutorial:

The operation of the circuit explained again. The circuit operates on a 3 to 4,5 volt power supply. You can use 2 AA batteries, I used my power supply for this. As soon as the power is switched on, the microphone is powered. When it responds to sound, it emits an electrical signal. This signal is coupled by capacitor to the first transistor amplification. The amplified signals are sent to second transistor base. Second transistor drives LED to emit light. The louder the sound, the brighter the LED.

I hope this Instructable has been of some use to you! Let me know what you thought of it in the comments. If you have made the circuit, I am very curious about the result and your experiences. Tips, tricks and other comments are of course always welcome!