• USB colour-changing light* - Using a USB lead Scouts can power a colour-changing LED which can then be placed inside a ping pong ball to make a glowing computer mascot.
This simple project demonstrates the use of a USB cable as a power source for an LED light. The colour-changing LED requires 5V, which is the same voltage as the USB cable delivers, so no additional resistance is needed for this circuit. If alternative LEDs are used, appropriate resistors will need to be added to the circuit as different coloured LEDs require different voltages.
The LED can be taped to the wire, or the two can be soldered together. Once they have put together the colour-changing LED, the Scouts can use it to light up a ping-pong ball with a hole cut in it. They could then draw an image on the outside of the ball, or add eyes whiskers and paper ears to make it in to a computer mouse.
USB power cable - Kitronik Code 4101 (https://www.kitronik.co.uk/4101-usb-power-lead.html)
10mm 5V Colour-changing LED - Kitronik Code 3544 (https://www.kitronik.co.uk/3544-colour-changing-10mm-diffused-led-750mcd.html)
Soldering equipment (optional)
Ping pong ball (optional)
Pens, paper and tape (optional)
Tools and equipment
Computer or USB power adapter for testing
• The Kitronik USB cables contain a positive and a negative wire only. Other USB cables are likely to contain four wires. Only the negative (black) and positive (red) wires are used in this project, any other wires should be ignored.
• USB cables that have a connector at both ends should be prepared by cutting off the connector on the opposite end to the standard USB plug.
• This is a good project for introducing soldering. The soldering is fairly straight-forward and mistakes can be corrected relatively easily and inexpensively.
• USB devices such as this can only draw up to 100mA from a computer. Devices that need more than this have to gain permission from the host computer through a process called negotiation.
Advice on soldering:
• Give Scouts only as much solder as they need for the project. The temptation to see what happens when a soldering iron is held against a whole reel of solder can be hard to resist!
• Lead-free solder can leave a residue on the tip of the soldering iron that stops it from working properly. This should be cleaned using a soldering iron tip cleaner.
Never clean soldering irons with an abrasive as this will remove their coating.
• The LED must be wired the correct way round to work.
• Short circuits can be caused by the two LED terminals making contact or bare wire from the USB cable making contact. This can be avoided by covering any exposed wire with insulating tape.
• For USB cables with more than two wires, make sure only the red and black power wires are used.
Meeting the aims of the electronics badge:
• Demonstrates that power can be drawn from different sources.
• Re-iterates learning about LEDs being polar and needing to be wired correctly to work.
• Basic soldering (optional).