Micro-controllers play an important role in today's electronics and DIY projects, most mirco-controllers have a large number of Input/Output pins, but in some cases that just is not enough. But being a digital device, there are a number of solutions and add on circuits to use, to overcome this problem one of the such devices is a demultiplexer. A demultiplexer can be used when you have to control a large amount of LEDs.
In this instructable I'm going to show you how to use a 3 to 8 demultiplexer using the arduino using this it is possible to control 8 LEDs with just 3 microcontroller pins.
Step 1: Tools and Components
Step 2: Circuit
The circuit to understand a Demultiplexer is quite simple, you can assemble it on a breadboard. The circuit consists of a 74hc138 IC which is a 3 TO 8 Line Decoder Demultiplexer. IT uses 3 I/O pins from the microcontroller it is connected to and uses it to control 8 lines, i.e you can control 8 LEDs with just 3 pins of the micro-controller. The 74HC138 has a voltage range of 2 to 6 volts so you can power it using any 3.3V microcontroller or a 5V microcontroller.
You will need to add a current resisting resistor suitable to the LEDs used.
Step 3: Going Further
The circuit can be assembled on a PCB or as an arduino shield, the image above shows the table of how to control the 8 lines, by supplying various combinations across the 3 input lines.
You could also add a separate 3.3V voltage regulator if you are working with LEDs.