FIRST CIRCUITS · 4 MIN READ

A first LED circuit

Start with something you can understand at a glance: a battery-powered LED with a resistor in series.

What you need

• A two-AA battery holder with a switch, and two 1.5 V alkaline AA batteries.
• A standard red indicator LED, a 330 Ω resistor and a solderless breadboard.
• A few jumper wires and the LED’s datasheet or pinout.

Understand the loop

The circuit is one continuous path: battery positive → resistor → LED anode → LED cathode → battery negative. The resistor limits current. It can sit on either side of the LED, provided it stays in series.

A red LED often has a forward voltage around 2 V. With a nominal 3 V supply and a 330 Ω resistor, the estimated current is (3 − 2) / 330, or about 3 mA. The exact brightness depends on the LED and batteries; check the part’s ratings.

Build it, one connection at a time

1. Check how your breadboard connects its holes. Place the two LED leads in separate electrical rows.
2. Identify the LED’s anode and cathode from its documentation. On many new LEDs the longer lead is the anode; the flat edge often marks the cathode.
3. Connect the battery’s positive wire to one end of the resistor, then its other end to the anode.
4. Connect the cathode to battery negative. Check that there is no direct connection between battery positive and negative.
5. Switch on briefly. If anything becomes warm, switch off and disconnect the batteries.

If it stays dark

Switch off first. Check the battery orientation, breadboard rows and LED polarity. Try a known-good LED if you have one. Never remove the resistor to make it brighter.

A useful next experiment

Switch off and replace the resistor with 680 Ω, then 1 kΩ. Compare the brightness. Record which value you used so that the observation is repeatable.