Computer Science • Logic Gates & Circuits
Circuit Dash
Each round shows a logic circuit and the value on every input. Follow the signals through the gates and call the output, Y — 0 or 1 — before the clock runs out. The circuits get bigger the longer you last.
Learning objectiveLogic gates · Boolean expressions
Work out the output of a logic circuit of up to three levels of gates for any combination of inputs, and link a circuit diagram to its Boolean expression.
By the end of a game you should be able to: recognise the AND, OR, NOT, NAND, NOR and XOR symbols; state each gate's truth table; trace values through a circuit one gate at a time; and read a Boolean expression such as Y = A·B + A̅·C as a circuit.
- Each circuit shows its inputs (A, B, C, D) on the left and the output Y on the right.
- Choose Y = 0 or Y = 1 — or press 0 / 1 on the keyboard.
- After each answer, every wire is labelled with its value so you can see how the output was reached.
- You start with 60 seconds. A correct answer adds time; a wrong one takes some away.
- Every three correct answers the circuits step up in size. Points = 10 × inputs × levels of gates, so bigger circuits score more. A NOT gate doesn't count as a level.
- In Standard mode the Boolean expression is shown under the circuit. In Advanced mode it isn't.
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Boolean notation
A · B or AB | A AND B |
A + B | A OR B |
| NOT A (a bar over the top) |
A ⊕ B | A XOR B — 1 when the inputs differ |
| A NAND B |
| A NOR B |
NOT is worked out first, then AND, then OR — just as multiplication comes before addition. Brackets change the order.
Working out a circuit
- Write each input's value on its wire.Where a wire splits (a dot), both branches carry the same value.
- Work through the gates from left to right.A gate can only be worked out once both of its inputs are known.
- Write each gate's output on the wire leaving it.A NOT gate (triangle and circle) simply flips 0 ↔ 1.
- The value reaching Y is the answer.Example: Y = A·B + A̅·C with A = 1, B = 0, C = 1 → A·B = 0, A̅·C = 0, so Y = 0.