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What you need:
3 crocodile-clip wires
9V battery
LEDs
Assorted resistors
Asparagus
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THE candle. It is a simple technology, and a good one. The electronic version is also simple to make, and is a great introduction to the concept of circuits 鈥� the cornerstone of many maker projects and core knowledge for the budding robot-builder.
Circuits are always complete loops that run from one terminal of a power source, such as a battery, to the other, going through some components on the way. The components are essential: connecting the terminals of the battery directly together will create a short circuit, and that鈥檚 bad news. The full energy of the battery will flow back on itself unimpeded, leading to heat and damage.
A component 鈥� an LED, say 鈥� tempers the flow by putting some of that energy to use. A couple of things to note about these little lights before you get going. First, they are polarised, which means current will only flow through them in one direction and so you have to attach them the right way round. Take a look at an . You will see that one leg is longer than the other. Just remember that the longer leg is positive.
The second point to remember is that LEDs are easy to fry. They tend to operate between about 1.5 and 3.5 volts (it will say on the packet), so connecting one to a 9V battery can be a death sentence. To prevent this, add a , which will dissipate some power and reduce current flow, bringing it down to a level where the LED is happy. To pick which resistor to go for, check what current the LED will take and either use (resistance = voltage / current) to work out the right resistor to use, or cheat and start with 300 ohms.
When you build your circuit, don鈥檛 touch any naked metal or you will get a shock. The small currents in this sort of circuit mean becoming part of it isn鈥檛 life-threatening, but it isn鈥檛 that comfortable. Take it from someone who knows.
Start with your 9V battery and connect its positive terminal (+ or red) to the resistor using a crocodile clip wire. Connect the other side of the resistor to the positive leg of the LED (green wire in the photo). Attach the other leg of the LED to the battery鈥檚 negative (black) terminal.
That鈥檚 it 鈥� you have made an electronic candle. Bask in the literal glow of success. Stick it on a bulldog clip and you can use it as a tiny reading light.
Experiment with different resistors. Higher values will make the LED dimmer, while lower values will make it brighter, until it burns out.
Bonus game: now you can play 鈥淲ill it Conduct?鈥� by adding anything from asparagus to jewellery to your circuit in place of one of the wires and see whether the LED lights up. Let me know what you find.
To download a printable version of this page click here
What you will need next week:
Piezo buzzer
Toaster
Tinfoil
Cardboard
Chopsticks
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Next in the series
1. Introduction
2. Electric candle: How to build a circuit
3. Toast notifier: Upgrade your circuit with switches
6. Magic eight ball
7. Theremin
8. Sound-sensitive disco ball
9. Rubbish sweeper
10. Biscuit bot
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