Build yours at home · Build 007
Dim the light
What we're doing
Build a real dimmer. Inside the kit's knob is a curved strip of carbon, the same stuff as pencil lead. Turning the knob changes how much of it the electricity goes through.
About 20 minutes.
Goes with these lessons
Get these parts
New to breadboards? See Getting set up- 4×AA battery holder with a switch (electronics shop or online)
- Breadboard, jumper wires, one LED, one 220 Ω resistor and one 10k knob (potentiometer) (Elegoo kit)
Fill each holder with the matching number of AA batteries (household).
Keep it safe
Battery power only, never household power. Use AA packs matched to the parts, not a 9V battery. A grown-up connects and disconnects the pack. Stop immediately if any part warms. Never join the pack's two metal ends: the wires can get hot. Coin cells stay with grown-ups, locked away. CPSC warns a swallowed button or coin cell can burn through a child's throat in about two hours; suspected swallowing needs emergency medical care immediately.
Keep the 220 Ω resistor in, so the LED never gets too much.
Steps
- 1
With the switch off, push the battery's red wire into the + line and its black wire into the − line.
- 2
Push the knob's three legs into three different rows. Call them left, middle and right.
- 3
Add a jumper wire from the + line to the knob's left-leg row.
- 4
Push the LED's long leg into the knob's middle-leg row and its short leg into an empty row.
- 5
Push one end of the 220 Ω resistor into the LED's short-leg row and the other end into the − line.
- 6
Switch on and turn the knob slowly. The light gets dimmer, then brighter. More carbon in the path, less light.
Not working? Turn the LED round. Then check it shares a row with the knob's middle leg.
- 7
Switch off and take the parts out.
Talk while you build
- What happens when the path through pencil lead gets longer?
- What did we change without changing the battery?
Spot it at home
- Dimmer switches, volume knobs, fan speed dials, and a tap that lets more or less water through.
What other knobs at home change 'how much'?
Grown-up extension
- Swap in different resistor values and compare the brightness.
- Add a potentiometer and turn it slowly while watching the LED.
More for grown-ups · printed parts
Optional equipment
Prints that make the build easier. None are required. Every build works with tape and clips.
Printables
A bigger knob that small fingers can turn without knocking parts off the breadboard.
Not printed yet
Grown-up references
A Beginner's Guide to Circuits · Øyvind Nydal Dahl Short projects that show what resistors and other common parts do in a circuit.