Breadboard simulator: plan and test circuits online

A breadboard simulator lets you try a circuit on screen before you push real parts into a breadboard, so you find the mistakes that burn out an LED or leave a loop open. Our Circuit Builder works as a breadboard simulator on a grid rather than on a picture of a breadboard: place cells, resistors, LEDs, switches, lamps, sensors and meters, wire them up, and it shows the voltage and current in every part as you build, with a warning when something would burn out. Plan the circuit there, then copy it onto your board.

Try it

Circuit Builder

Build any DC circuit with meters, lamps, LEDs and sensors, and see live readings

Open the simulatorGo to its page

Is it a breadboard simulator?

Not in looks. You won't see holes, jumper wires or a battery clip: you build a circuit diagram on a dot grid, the way you would sketch the circuit before building it. The electrical result is what a breadboard would give you, because a breadboard is only a way of joining parts. Strips of holes joined underneath act as wires, so any breadboard layout can be drawn as a circuit diagram, and the other way round.

It simulates direct current (DC) circuits made from these parts: cells with an optional internal resistance, resistors, variable resistors, filament lamps, LEDs, switches, thermistors, light-dependent resistors (LDRs), ammeters and voltmeters. It doesn't have transistors, capacitors on the build grid, chips such as a 555 timer, an Arduino or AC supplies. For those, use a simulator made for electronics projects. The online circuit simulator guide covers everything else it does, including its guided circuits.

How a breadboard is connected

A solderless breadboard has metal clips under its holes. On a standard board each row of ten holes is split by a gap down the middle into two strips of five, and the five holes in a strip are joined. The long power rails down each side, marked + and −, are joined along their length. The two sides aren't joined to each other, and some larger boards split each rail halfway, so check with a multimeter.

The centre gap is there for chips: a chip straddles it so that each of its legs lands in its own strip. The rule that matters most is that a part's two legs go in different strips. Push both legs of an LED into the same strip of five and the clip joins them, so no current goes through the LED.

How to build a breadboard circuit in the Circuit Builder

1. Open the Circuit Builder. It opens in Build a circuit mode on a starter circuit: a cell, a switch, an ammeter, a lamp and a voltmeter. Press the bin button to clear the grid, or pick from Load an example.
2. Pick a part from the parts row, such as Cell, then click a gap between two dots to place it. The cell stands in for your battery or power supply.
3. Choose Wire and drag from dot to dot to join parts, the way jumper wires and strips join them on the board. Make sure the loop goes all the way back to the cell.
4. Choose Select and click a part to set its values: the cell's voltage, a resistance, an LED's forward voltage and maximum current. Press F, or the flip button, to turn an LED or meter round.
5. Read the table of every part's voltage, current and power, and any warnings. Click a switch on the grid to open or close it.

The warnings tell you what would go wrong on the bench: an LED with nothing to limit its current, an LED the wrong way round, a lamp well above its rated power, a part shorted out by a wire across it, or a loop that isn't closed.

Example: an LED on a 9 V battery

The first circuit most people build on a breadboard is an LED with a resistor. Use the Circuit Builder's default LED values, a forward voltage of 2 V and a maximum current of 20 mA (check your own LED's datasheet). The resistor takes the rest of the supply voltage, so for a current of 15 mA:

Resistors come in standard values, so round up to the next one, 470 Ω. Build it: a 9 V cell, a 470 Ω resistor, an ammeter and an LED in one loop. The ammeter reads 14.9 mA and the LED lights. Now change the resistor to 330 Ω, a value you might grab from a kit. The current rises to 21.2 mA, over the LED's 20 mA maximum, and the Circuit Builder marks the LED Burns out. Take the resistor out altogether and it warns that the LED would burn out instantly.

On a real LED the longer leg is the anode, the + side. Flip the LED in the Circuit Builder and no current flows, and it tells you the LED is reversed: the same thing that happens when you push one into the board backwards.

Example: a light sensor

A light-dependent resistor in a voltage divider gives a voltage that changes with brightness, which is how a night light knows it is dark. Build a 9 V cell in a loop with a 10 kΩ resistor and an LDR, with a voltmeter across the LDR. Select the LDR and drag its light level slider:

The darker it gets, the bigger the LDR's share of the 9 V. The Thermistor sensor example in Load an example does the same with temperature: its voltage falls as the thermistor warms. The voltage divider calculator guide explains the formula behind these numbers.

From the simulator to the breadboard

1. Draw the loop in the Circuit Builder first and check every current against each part's rating.
2. On the board, run the battery to the + and − rails.
3. Give each junction in your diagram its own strip of five: everything that meets at one dot in the Circuit Builder goes in the same strip.
4. Put each part's two legs in different strips, with an LED's longer leg towards +.
5. Measure with a multimeter where the Circuit Builder had meters: in series for current, across a part for voltage. The readings should match the simulation, give or take your parts' tolerance.

Common mistakes

• Both legs in one strip. The clip joins them and the part is shorted out. The Circuit Builder marks this Shorted.
• No resistor with an LED. Nothing limits the current and the LED fails.
• The LED backwards. No current flows. The longer leg goes towards +.
• Assuming the rails run the whole length. On split-rail boards, join the two halves with a wire.
• An ammeter across a part. An ammeter has almost no resistance, so across a part it shorts it out. It goes in series.
• A voltmeter in series. Its very high resistance stops the current. It goes across a part.

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Physics · Electricity and magnetismOnline circuit simulator: build DC circuits, read metersBuild DC circuits online with cells, resistors, lamps, LEDs, switches, sensors and meters, and see every voltage and current live, with worked examples.