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How to Use a Breadboard: How the Holes Connect, Power Rails and a First LED Circuit

Probot Studio

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What we'll do

  1. Look inside a breadboard and see which holes connect to which.
  2. Use the + and − power rails the right way.
  3. Build first circuits with an LED, a resistor and a button.
  4. Find and fix the 5 most common mistakes on a virtual breadboard.
  5. See how to measure current on a breadboard.

Why it's useful: a breadboard lets you build, pull apart and rebuild circuits without soldering. Most circuits that "just don't work" come down to one thing: not knowing which holes are connected inside.

Breadboard drawing: the left half shows the holes from the top, the right half the metal strips under the plastic; in each column a-e is one strip and f-j another, with + and − rails running along the edges

What is a breadboard and what is it used for?

A breadboard is a board full of holes for building circuits without solder. You push a leg into a hole and metal spring clips inside both hold it and connect it. The holes are 2.54 mm (0.1 in) apart, so LEDs, resistors, chips and an Arduino Nano plug straight in.

Size Holes Layout
Mini 170 17 columns × 10 holes, usually no power rails
Half 400 30 columns × 10 holes + 4 rails × 25
Full 830 63 columns × 10 holes + 4 rails × 50

How are the holes on a breadboard connected?

In each column, the 5 holes from a to e share one metal strip inside; f to j is a separate strip. The center gap splits the two sides. The rails on the edges are connected end to end.

Breadboard + and − (power rails)

Wires from the Arduino 5V and GND pins go into the + and − rails and a glow runs along the + rail; below, a rail split in the middle with a bridge wire across the gap

The long rows along the edges are the power rails: red-lined + (5 V) and blue-lined − (GND). You feed power into the rail once and every part takes it from there.

Building an LED circuit on a breadboard

Two panels: on the left, wrong, both LED legs in the same 5-hole strip and the LED stays dark; on the right, right, the legs in two separate strips side by side and the LED lit

There's one rule: each part's two legs go into two different strips, and ends that should connect share a strip.

  1. Red wire: + rail → a5.
  2. 220 Ω resistor: c5 → c9. A resistor has no direction. To read its value, see the resistor color code.
  3. LED: long leg (anode) in e9, short leg (cathode) in e10. The LED rim is flat on the short-leg side.
  4. Black wire: a10 → − rail.

Current flows from the + rail through the resistor and the LED back to the − rail. With 5 V, a red LED (about 2 V) and 220 Ω, that's about (5 − 2) / 220 ≈ 14 mA.

Two LEDs in parallel: give each LED its own resistor, and connect each one between + and − on its own path.

Try it: a virtual breadboard

First tap a hole and see what lights up; then, on the Find the mistake tab, fix 5 circuits whose LED won't light.

This is an interactive half-size breadboard: tap any hole to light up every hole connected to it, then find and fix the faulty part in five LED circuits. It needs JavaScript. If it didn't load, the inside-view drawing and the steps above cover the same ground.

Wiring a button on a breadboard

Button circuit on a breadboard: from the + rail into the button, from the button through a 220 ohm resistor to the LED, from the LED to the − rail. The button sits across the gap; pressing it lights the LED

The button sits across the center gap; pressing it joins its left and right leg pairs and the LED lights. Four-leg buttons have their legs connected in pairs inside; if you're not sure which pair is which, check with the continuity mode of a multimeter.

To read the button with an Arduino, wire it to pin 2 and GND and use INPUT_PULLUP: the code is in What is Arduino.

Simple breadboard circuits to try

Mini breadboards and breadboard power modules

Measuring current on a breadboard

One resistor leg pulled out of its strip, the red multimeter probe in the empty strip and the black probe on the loose leg; the meter on its mA range shows about 13.6 mA

To measure current, the multimeter goes into the loop (in series): you open the circuit at one point and close the gap with the meter. To measure voltage you don't open anything; the probes just touch two points.

Common mistakes

Symptom Cause Fix
LED dark, legs in the same column Both legs in one strip Move one leg to the next column
LED very bright and hot Resistor in one strip, or missing The resistor must bridge two strips
Everything looks right, LED dark LED backwards Long leg toward +
Half the board does nothing Split rail, or the other edge has no power Wire across the split or between the edges
The circuit cuts in and out Leg not fully seated, thin leg Straighten the leg, try another hole
The Arduino keeps resetting + and − rails shorted by a wire Unplug USB right away, check the wires

Sources

Accessed: 17 October 2026