Build a Basic LED Circuit
The first circuit most electrical engineers ever build — small, fast, and it teaches you why every component in a circuit exists for a reason.
Related field: Electrical Engineering
Mission Briefing
Objective
Build a working circuit that lights an LED safely, using a battery, a resistor, and a breadboard.
Constraints
- The LED must be connected with correct polarity — it will not work backward
- A resistor must be included in the circuit to limit current
- Only the listed components and a single power source are allowed
Concept You're Testing
Current, polarity, and current-limiting resistors — why an LED only works in one direction, and why connecting it directly to a battery without a resistor is a bad idea.
What You'll Need
- A small breadboard
- A 9V battery with a battery clip, or an AA battery holder (2–4 batteries)
- One LED
- One 220–330 ohm resistor
- 2–3 jumper wires
Instructions
- 1Look closely at the LED: one leg is longer than the other. The longer leg is positive and must connect toward the battery's positive side — LEDs only work in one direction.
- 2Place the LED into the breadboard so its two legs sit in different rows (not the same row, or it will short out).
- 3Connect one leg of the resistor to the same row as the LED's positive (longer) leg, and leave the other end of the resistor free for now.
- 4Connect a jumper wire from the free end of the resistor to the battery clip's positive wire.
- 5Connect a second jumper wire from the LED's negative (shorter) leg row to the battery clip's negative wire.
- 6Connect the battery. The LED should light up immediately.
- 7If it doesn't light up, double-check the LED's direction first — reversed polarity is the most common reason a first circuit doesn't work.
- 8Optional: try removing the resistor briefly to see what changes, then put it back — this demonstrates why the resistor is there in the first place, not just a spare part.
How to Measure Results
Success is simple and binary: the LED lights up. If it doesn't, the circuit isn't complete or correct yet — that's useful information, not a failure.
Skills You'll Practice
- Reading component polarity — why direction matters in a circuit
- Why a current-limiting resistor is necessary, not optional, when using an LED
- Basic breadboard layout and how its rows are electrically connected
- Methodical debugging — checking one likely cause at a time when something doesn't work
If It Doesn't Work the First Time
That's normal — this challenge follows the same design process real engineers use. A failed test just tells you where to go back and improve.
Figure out what problem you're actually solving, and what would even count as success. Skip this step and jump straight to building, and a lot of bad designs happen right here.