My First LED Circuit
Battery, switch, resistor, LED. A classic first circuit, built on a breadboard with no soldering.
What you’ll make
A battery pack, a switch, a resistor and an LED, built on a breadboard with no soldering. Flip the switch and your LED lights up. It’s a classic first circuit.
What you need
- A battery holder for 3 AA batteries, with an on/off switch and wire leads (red and black)
- 3 AA batteries, all new and the same type
- 1 red LED, 5 mm
- 1 resistor, 220 Ω, ¼ watt (bands: red, red, brown; on a five-band resistor: red, red, black, black, brown)
- A small solderless breadboard
- 2 or 3 jumper wires
- Optional: a multimeter
Cost: low. These parts are inexpensive, and most beginner electronics kits include all of them.
No 3-AA holder? A 2-AA holder (3 V) also works with a red LED and the same 220 Ω resistor. The LED will be dimmer. Don’t use a 9 V battery with this resistor; Lesson 5 shows why.
Safety numbers for this build
| Supply | 3 V to 4.5 V (2 or 3 AA batteries) |
|---|---|
| Expected LED current | about 11 mA at 4.5 V; about 4.5 mA at 3 V |
| Heat in the resistor | about 0.03 W, far below its 0.25 W rating |
| Supervision | An adult nearby for younger builders |
Build it, step by step
- Batteries in, switch off. Put the batteries in the holder, matching + and −, and make sure the switch is off.
- Place the LED. Push the LED into the breadboard so its two legs are in two different five-hole rows. Note which row has the long leg (anode).
- Add the resistor. Push one resistor leg into the same row as the LED’s long leg. Put the other resistor leg in an empty row.
- Connect to the rails. Run a jumper wire from the resistor’s free row to the red (+) rail. Run another from the LED’s short-leg row to the blue (−) rail.
- Connect the battery pack. Push the red lead into the red (+) rail and the black lead into the blue (−) rail. If the leads are soft and stranded and won’t go in, use a holder with solid or tinned wire ends, or jumper wires with alligator clips.
- Switch on. Your LED should glow a steady red. Switch off, and it goes dark instantly.
It doesn’t light? Check these in order
- Is the battery switch on, and are the batteries in the right way round?
- Is the LED backwards? The long leg must connect (through the resistor) to +.
- Are both LED legs in the same five-hole row? Move one.
- Is the resistor really sharing a row with the LED’s long leg?
- Are the rails split halfway along your breadboard? Keep everything on the same half, or bridge the gap with a wire.
- Still dark? With a multimeter on DC volts, check the battery pack reads about 4.5 V (3 fresh AAs usually read a little more).
Measure it (optional)
With the LED lit, set a multimeter to DC volts and measure across the resistor, then across the LED. Expect roughly 2.5 V across the resistor and about 2 V across the LED (your numbers will differ a little). Add them: they should come close to the battery voltage. Then work out the current: I = Vresistor ÷ 220.
Take it further
- Swap the 220 Ω resistor for a 1 kΩ (brown, black, red). Predict the new current, then look: dimmer?
- Add a second LED with its own 220 Ω resistor between the same rails. Now you have two branches: a parallel circuit.
- Try a yellow LED. Then try a blue one on 2 AA batteries (3 V). It will glow only faintly, if at all. Lesson 5 explains why it struggles.
For teachers and parents
Open the teacher guide
Time: 10 to 15 minutes to prepare; 30 to 45 minutes in class.
Learners will: build a complete series circuit from a diagram; identify LED polarity; explain why the resistor is needed; predict and test what happens when the circuit is opened or the LED reversed.
Per student or pair: the parts list above. Have spare LEDs and resistors on hand.
Risk and supervision: low. Battery power only. Check every battery pack is switched off before building starts. Watch for loose batteries being shorted against keys or coins in pockets.
Common misconceptions: “The LED uses up the current” (no: the current is the same all the way around; the LED converts energy). “The resistor makes it brighter” (no: it limits current to protect the LED). “Only the wire to + matters” (current needs a complete loop).
When it doesn’t work: nine times out of ten it’s a reversed LED or both legs in one row. Use the checklist above with the class; troubleshooting is part of the lesson.
Discussion questions: What happens everywhere in the circuit when the switch opens? Why does the LED only work one way? What would happen without the resistor?
Worksheet with answers:
- Draw the circuit using schematic symbols. (Battery, switch, resistor and LED in one loop, LED triangle pointing away from +.)
- The battery is 4.5 V and the LED needs 2.0 V. How many volts are left for the resistor? (2.5 V.)
- Use I = V ÷ R to find the current through the 220 Ω resistor. (2.5 ÷ 220 ≈ 0.011 A, about 11 mA.)
- Predict: with a 1 kΩ resistor, brighter or dimmer? (Dimmer: about 2.5 mA.)
Stretch: add a second LED in parallel with its own resistor, and explain why each LED needs its own.
Curriculum note: circuits and electricity appear in elementary and junior high science in Alberta and across Canada. Check the current Alberta program of studies for exact outcomes.
Learn more
- Lesson 5: LEDs and resistors
- Virtual Workbench: try other resistors and LEDs on screen
- Science World: Build a Circuit: a simple classroom circuit activity
- Next build: Conductor or insulator?
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.