Add parts
Drag gates, switches, clocks, flip-flops and displays onto the grid, or tap a part to drop it in the middle. Start from an example if you like.
Free Logic Circuit Simulator
Build digital circuits from gates, switches, clocks, flip-flops, LEDs and 7-segment displays, then flip the switches and run the clock to see every wire light up. Turn any circuit or Boolean expression into a truth table with its simplest sum of products, or build a circuit from an expression in one click.
Open Logic Circuit Simulator →How to simulate a logic circuit
Wire them
Drag from an output pin to an input pin, or tap one pin and then the other. Wires turn green when they carry a 1.
Simulate
Click switches to change inputs, press Run to start the clocks, step one tick at a time, and open the truth table to see every input combination.
Tips for clear circuits
Name your inputs and outputs
Labels on switches and LEDs become the column names of the truth table and the variables of the simplified expressions.
Let the table simplify for you
Fill in a truth table or type an expression, then build the simplified circuit: fewer gates, same behaviour.
Use feedback for memory
Feed a gate's output back into an input to build latches and memory. If a loop never settles, the simulator flags it and highlights the parts involved.
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Logic circuit simulator FAQ
Is this logic circuit simulator free?
Yes. It's a free online logic simulator with every part and feature included, as many circuits as you like, no account and no watermark on exported images.
How do I simulate a logic circuit online?
Add switches, gates and LEDs, connect pins to wire them, then flip the switches and watch the outputs respond. It all runs in your browser with nothing to install, and ready-made examples help you get started.
Which logic gates and parts are included?
Switches, push buttons, clocks and constants; AND, OR, NOT, NAND, NOR, XOR, XNOR and buffer gates with 2 to 8 inputs; D, JK and T flip-flops; LEDs in five colours, a 7-segment display, a hex display and text labels.
How do I make a truth table from a circuit?
Open the Truth table tab. Use your circuit (switches are the inputs, LEDs the outputs), type a Boolean expression, or fill in a table yourself. You get the minimal sum of products and product of sums, the minterm and maxterm lists, and a CSV download.
Can I turn a Boolean expression into a circuit?
Yes. Type the expression in the Truth table tab and build the simplified circuit with one click: fewer gates, same behaviour, ready to test with switches and LEDs.
Which expression syntax can I use?
AND as A·B, A*B, A&B, A AND B or just A B; OR as +, |, OR; NOT as A', !A, ~A or NOT A; XOR as ^, ⊕ or XOR; plus NAND, NOR, XNOR, -> and <->. Several outputs go on separate lines as F = …. When all names are capitals, letters next to each other multiply, so AB' means A·B'.
Can I build sequential circuits with flip-flops and clocks?
Yes. D, JK and T flip-flops react to the rising edge of their clock, so you can build counters, shift registers and other sequential logic and step through them. If a feedback loop never settles, the simulator pauses and highlights the parts involved.
How big can a circuit be?
Up to 2,000 parts per circuit, with truth tables of up to 12 inputs and simplification of up to 10 variables: plenty for digital logic coursework, lab prep and hobby projects.
Does it work on a phone or tablet?
Yes. Tap a part to add it, drag parts to move them, tap one pin and then another to wire them, and pinch to zoom. The parts and details panels fold away to leave room for the circuit.
How do I save or share a circuit?
Your circuit is kept in this browser automatically. Save a circuit file to keep a copy or open it on another computer, copy a share link, or download the drawing as PNG or SVG.
Are my circuits uploaded?
No. The simulation runs in your browser and the current circuit is saved in this browser's storage on your device. A share link carries the circuit after the # sign, which browsers never send to a server.
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