Build a circuit from its rule

5 minAS Level3.2.4

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can construct a logic circuit from a problem statement, an expression or a truth table.

Treat the expression like a wiring recipe

For example, let A and B name inputs and Y name the output. If Y is 1 only when A is off and B is on, put A through NOT, then feed NOT A and B into AND.

Build the smallest operation first, then connect its output to the next gate. Each input letter gets its own wire.

For Y = (NOT A) AND B, first invert A. Then feed NOT A and B into a two-input AND gate.

Worked example: From sentence to gates

Output Y is 1 when A is off and B is on.

Have a go first?

Pick the gate plan

Multiple choiceQuestion 1 · Apply

Y should be 1 when A is off and B is on. Which circuit plan matches?

APut A through NOT; connect NOT A and B to AND; label its output YBPut A and B into OR, then invert its outputCPut A and B directly into ANDDPut A through NOT, then connect NOT A and B to OR

Multiple choiceQuestion 2 · Stretch

Which gate sequence builds Y = A OR (NOT B)?

ASend B through NOT, then connect A and NOT B to ORBSend A through NOT, then connect NOT A and B to ORCPut A and B into AND, then invert the outputDConnect A and B directly to XOR

Answer the 2 questions above to continue.

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