Introduction: LEDs Switches

This article shows you how to build a simple LED switching circuit.

I used big LEDs and switches from an old PC (personal computer) and VCR (video) cassette recorder. You can use smaller LEDs.

You can implement this circuit with just two switches and two LEDs.

Supplies

Parts: LEDs - 4, Piece of cardboard or matrix board, 100-ohm resistors - 5, switches - 3 or 4, 1 mm metal wire, wires, power source (2 AA or 2 AAA batteries, battery harness).

Tools: pliers, wire stripper (this tool could be optional if you are not using insulated wires - you do not need insulated wires for this circuit if the switches come with wires attached).

Optional parts: solder, scissors for the wire stripping (not a good idea in my opinion).

Optional tools: multimeter, simulation software, soldering iron.

Step 1: Design the Circuit

The circuit above is showing only three switches but you can connect the grounded cathode LED1 to switch. Then you will have additional control. The white LED that you have seen in the video actually conducts in both directions and changes colour with the current direction.

The maximum LED current will equal to:

IledMax = (Vs - Vled) / Rd1 = (3 V - 2 V) / 100 = 10 mA

The minimum current is only possible LED2 and LED3 are unique LEDs and conduct in both directions. When switch 1 and switch 3 are shorted the total current for two LEDs will equal to:

2*IledMin = (Vs - Vled) / Rd2 = (3 V - 2 V) / 100 = 10 mA

Divide this current by two because the current will split in half we get 5 mA.

You should not raise the power supply voltage. This might burn the LEDs. However, those big LEDs might need a current slightly higher than 10 mA.

Step 2: Make and Test the Circuit

I did not use a soldering iron at all. I twisted the wires together with pliers.

The piece of cardboard has many holes because I tried implementing other circuits that were not good enough to be published anywhere on the internet.

The video is showing me gradually turning OFF the switches and thus the LEDs sequentially turning ON, one after another.

I suggested that you purchase more than three LEDs because you can easily burn the LEDs if you are not patient.