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Half adder from CMOS NAND gates

Logic Gates from Components · free online experiment, runs in your browser with no install or sign-up.

Open this experiment in the circuit simulator

Objective

Add two bits using transistor-level gates: sum = A ⊕ B, carry = A·B.

Procedure

Use the Controls tab (or the batteries' Properties) to set each input to 0 V or 5 V and press Start Simulation; turn Live on and drag an input slider to watch the output.
The green LED is the sum, the yellow LED the carry.

Theory

Four NAND gates make the XOR (sum), a NAND plus an inverter make the AND (carry): 5 gates, 22 transistors.

Questions to answer

Count the transistors.

Components used

9 × 2N7000 N-MOSFET, 9 × BS250 P-MOSFET, 3 × Battery / DC source, LED 5mm Green, LED 5mm Yellow, 2 × Panel voltmeter, 2 × Resistor 220 ohm 1/4W

About the model

Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.