Irby Electronics

Irby Electronics

6.      Assembly is now complete. Check that any bare wires are not touching each other. Place three new AA batteries into the battery box and switch on.


  • If your circuit doesn’t work and the batteries become hot then you have made a short‑circuit. This is a potential fire hazard! Switch off immediately, remove the batteries  and check your circuit to find the problem before continuing.
  • If the problem isn’t a short‑circuit, please recheck your soldering and your batteries.

completed circuit

showing soldered joints

Think  SAFETY.   Act  SAFELY.

You're important . . . so also read through the safety guidance sheet provided with the kit.

3.      Bend the negative lead of the l.e.d. so that it lies flat on the foam board and, using pliers, bend the end of this lead into a small hook as shown:

Some marking of the surface of the foam board is unavoidable during construction but this can be minimised by careful handling. Only three joints are needed to complete the circuit and soldering is not essential. The connections could be made by just twisting wires together but a soldered joint makes a better electrical connection.

1.      Position the foam board so that the removable REVERSE label is on the underneath surface and normally hidden from view. Screw the foam board to the wooden supports. Push the leads of the l.e.d. through the pin holes in the middle of the foam board until the base of the l.e.d. lies flat on the foam board.

2.      Identify the positive and negative leads of the light-emitting diode. A light-emitting diode will not work if it is connected the wrong way around and so correct identification of the leads is important! For this type of l.e.d., the negative lead is shorter and it is next to the flattened edge on the l.e.d. capsule:

Skill level:      *            BASIC       
Project constructed on foam board.
Soldering recommended but project could be made by simply twisting wires together.

This is a very simple circuit containing a single light-emitting diode. The circuit diagram is shown below. The same circuit is used in Project 7 but Project 7 is constructed on track board.

close-up of hook on

negative lead of l.e.d.


negative lead next to

flattened edge on l.e.d.

A resistor is usually connected to a light-emitting diode (l.e.d.) to reduce the amount of current flowing in the circuit. Too much current can cause the l.e.d. to burn out. In this circuit, a 47 ohm resistor (R1) is connected to the l.e.d. (D1).

The “surprise” about this circuit is that such an ordinary-looking l.e.d. can produce such a colourful display. For a really spectacular display, place a cut-glass container such as a tumbler or a tea light holder over the l.e.d.

The l.e.d. changes colour over about 30 seconds and then the cycle repeats. Unfortunately, it is not possible to alter the rate at which the l.e.d. changes colour.

This project requires three AA batteries (not supplied in this kit). In a test of this circuit, a set of Duracell Plus Power batteries was still producing a good output of light after 140 hours of continuous use.

To construct this project you will need to use the following tools (not supplied):

  • small, low power soldering iron, e.g. 15 watt, 18 watt or 25 watt (only needed if soldering is to be attempted)
  • small pliers for bending component leads
  • slotted screwdriver for securing foam board to wooden base.

Assembly Instructions for Project 1: L.E.D. Surprise 1
Please read through these instructions very carefully before starting assembly.

Twist the black lead from the battery box around the hook on the negative lead of the l.e.d. and solder them together, avoiding touching the foam board with the soldering iron.

4.      Using pliers, bend the ends of the leads of the resistor to form small hooks. It does not matter which way around a resistor is connected in a circuit. Bend the positive lead of the l.e.d. in the opposite direction to the negative lead and make the end of the positive lead into a small hook. Twist one end of the resistor and the end of the positive lead of the l.e.d. together and solder them.

5.      Twist the red lead from the battery box around the other end of the resistor and solder them together. Your circuit should look like that in the picture below: