Adder Circuit Builder
Explore half adders, full adders, and 4-bit ripple carry adders with interactive inputs and circuit diagrams. Matches AQA A Level CS (7517) specification §4.6.5.5.
📖 Learn Step-by-StepA half adder adds two single-bit inputs using an XOR gate (sum) and an AND gate (carry). It cannot accept a carry-in from a previous stage.
Truth Table
| A | B | Sum | Carry |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 1 |
Working
- Inputs: A = 0, B = 0
- XOR gate: A ⊕ B = 0 ⊕ 0 = 0 → Sum = 0
- AND gate: A ∧ B = 0 ∧ 0 = 0 → Carry = 0
- Result: 0 + 0 = 00 in binary (0 in decimal)
Adder Circuit Practice Questions
Half adder: Sum output
Half Adder — Inputs:
Select the outputs:
Half adder: A=1, B=0
Half Adder — Inputs:
Select the outputs:
Full adder: A=1, B=1, Cin=1
Full Adder — Inputs:
Select the outputs:
Full adder: A=0, B=1, Cin=1
Full Adder — Inputs:
Select the outputs:
Full adder: A=1, B=0, Cin=0
Full Adder — Inputs:
Select the outputs:
Quick reference — adder circuits
Half adder
Adds two single bits. Uses an XOR gate for the sum and an AND gate for the carry. Cannot handle a carry-in.
Full adder
Adds two bits plus a carry-in. Built from two half adders and an OR gate. Can be chained to add multi-bit numbers.
Ripple carry adder
N full adders chained so each carry-out feeds the next carry-in. Adds two N-bit numbers. Called “ripple” because the carry propagates from LSB to MSB.