LED Voice Flasher


This circuit is commonly called MUSIC COLOUR  as the LEDs flash and blink in time with the music.
It uses two transistors to amplify the signal from the microphone to drive the LEDs. It will  operate from 3v to 5v. Do not use a voltage above 5v as the output does not have a current-limiting resistor and the LEDs will be destroyed.

Principle of Operation
The signal from the microphone is about 20mV and the current is less than 1mA. The LEDs require a signal of 4v and at least 100mA to produce a bright flash.
The two transistors amplify both the voltage and current to achieve this requirement.
The first transistor increases the voltage but this is not an important factor as most of the voltage amplification takes place with the second transistor.
The first transistor accepts the current from the microphone and when combined with the current from the 1M base resistor, the transistor  turns ON more and turns OFF slightly (due to the waveform). This action is passed to the second transistor where the 10k resistor turns the transistor ON and the first transistor turns the second transistor OFF slightly by robbing the base of current from the 10k resistor.
The 10k resistor allows a maximum of 0.5mA to flow into the base of the second transistor and if this transistor has a gain of 200, the collector-emitter current will be 100mA. This current flows through the 5 LEDs and is shared equally to pass about 20mA through each LED. We are using the transistor and 10k as "current-limiting" and that's why the supply must not be increased above 5v.

The Circuit

The video shows the LEDs flashing in time with voice and music.
Use a constant-heat soldering iron (320 degrees C) and fine solder (0.8mm).
Fit one component and splay the legs slightly so it doesn't fall out of the holes. Turn the board over and hold the soldering iron on one side of the lead and the solder on the other side. The solder will melt and flow across to the iron. This will take less than one second.
Snip the leads close to the solder-joint. Solder one component at a time. Use the photo below to identify the components and how they are fitted to the board. All the components must be fitted around the correct way and there is only one way to fit them.
The microphone has two short wires with one wire connected to the frame of the microphone. This is the negative lead. The 3 resistors can be fitted around either way as they are classified as a "non-polar component."

The photo above shows all the components fitted to the board. The flat on the side of the LED identifies the cathode lead (the short lead is the cathode). The placement of the two electrolytics must be observed. The 3 resistors are 4k7, 1M and 10k.
Connect a 3v to 5v supply to the 2-terminal connector with the negative on the left and the positive on the right. The circuit will not be damaged if the supply is reversed, but it will not work.
 

You can buy this kit for about $3.50 post-free

21-7-2013