A resistor is usually connected to a light-emitting diode to reduce the current flowing through it in a circuit. Too much current can cause the l.e.d. to burn out. However, these are special l.e.d.s and they do not require resistors.
All of the positive leads of the l.e.d.s are connected to the positive side of the battery. All of the negative leads of the l.e.d.s are connected to the negative side of the battery. This is an example of a circuit in which the components are connected “in parallel”.This project requires two 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 90 hours of continuous use.
To construct this project you will need to use the following tools (not supplied):
Assembly Instructions for Project 15: Christmas Star L.E.D. Display
Please read through these instructions very carefully before starting assembly.
Think SAFETY. Act SAFELY.
You're important ... so also read through the safety guidance sheet provided with each kit.
9. Cover the negative leads and negative link wire with pieces of insulation tape. Cover the junction of the black cable and green cable with a small piece of insulation tape. This will prevent a hazardous short‑circuit occurring should a positive part of the circuit accidentally touch the negative link wire. To aid clarity in the picture below, yellow insulation tape was used to cover the negative link wire but black insulation tape is supplied in the kit.
10. Make the end of each positive lead into a small hook. Connect all of the positive leads of the l.e.d.s together by passing the remaining piece of link wire through each of the hooks. Squeeze each hook and link wire connection together using pliers and solder the five joints. Trim excess link wire using wire cutters.
11. Twist the end of the red extension cable around the positive link wire at any convenient position and solder them together. Twist the other end of the red cable around the end of the red lead from the battery box and solder them together. It is not necessary to cover the positive link wire with insulation tape. Your circuit should look like that in the picture below:
(negative part of circuit covered with yellow insulation tape)
8. Take the extension cable and twist one end of the green cable around the negative link wire at any convenient position and solder them together. Twist the end of the black lead from the battery box around the other end of the green cable The picture below shows this stage of construction:
soldered link wire
connecting the negative
close-up of a link wire
and hook connection
Skill level: * BASIC
Project constructed on foam board.
Soldering recommended but project could be made by simply twisting wires together.
This circuit contains five light-emitting diodes (l.e.d.s) arranged on a star-shaped piece of foam board. The foam board circuit is attached to the battery box by a short extension cable which allows the star to be dangled from the branch of a Christmas tree whilst the battery box is hidden from view. The l.e.d.s flash independently at slightly different rates to produce a sparkling display.
The circuit diagram is shown below. The same circuit has been used in earlier projects.
Some marking of the surface of the foam board is unavoidable during construction but this can be minimised by careful handling. The connections between the components 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 underneath. Choose one of the l.e.d.s and gently push its leads through one of the pairs of pin holes on the top surface. Continue pushing until the base of the l.e.d. lies flat on the surface of the foam board.
2. Identify the positive and negative leads of the l.e.d. 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 is nearest to the flattened edge on the l.e.d. capsule (see picture below).
PROJECT 15: CHRISTMAS STAR L.E.D. DISPLAY
green lead of extension cable attached to negative link wire
12. Assembly is now complete. Check, again, that the bare positive link wire is not touching the negative link wire at any point. Place two new AA batteries into the battery box and switch on.
3. Bend the negative lead of the l.e.d. so that it lies flat on the REVERSE side of the foam board and points towards the centre of the star.
4. Choose a second l.e.d. and push its leads through another pair of pin holes on the top surface. Bend the negative lead so that it lies flat on the REVERSE side and points towards the centre. Repeat this procedure with the three remaining l.e.d.s.
5. Using pliers, bend the end of each negative lead into a small hook as shown below:
6. Bend the positive leads of the l.e.d.s so that they lie flat on the foam board and away from the negative leads. To avoid confusion with the negative leads, do NOT bend the ends of the positive leads into hooks at this stage of construction!
7. Pass the length of link wire through each of the hooks on the negative leads and squeeze the hook and link wire connections together using pliers. Trim the excess link wire using wire cutters. Solder the five joints, taking care to avoid touching the foam board with the soldering iron. All of the negative leads of the l.e.d.s are now connected together.
negative lead next to
flattened edge on l.e.d.
close-up of a hook on negative lead of l.e.d.
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