IntermediateDisplays & Logic
Single-Bit Full-Adder Trainer
Build a one-bit full adder from XOR, AND, and OR gates, then check sum and carry for all input combinations.
Parts from the database
Other supplies
- breadboardCommon build supply
- 5 V supplyCommon build supply
- three switchesCommon build supply
- three 10 kฮฉ pull-downsCommon build supply
- two LEDsCommon build supply
- two 1 kฮฉ resistorsCommon build supply
- three 100 nF capacitorsCommon build supply
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Connections
- Power each DIP-14 at pin 14/+5 V and pin 7/ground with 100 nF. Switches with pull-downs provide A, B, and Cin.
- HC86 gate pins 1/2โ3 makes P=A XOR B; pins 4/5โ6 make Sum=P XOR Cin.
- HC08 gates pins 1/2โ3 make G=A AND B; pins 4/5โ6 make H=P AND Cin.
- HC32 gate pins 1/2โ3 gives Cout=G OR H. Show Sum and Cout on LEDs. Tie unused inputs low.
Build steps
- Build and check A XOR B first.
- Add the second XOR and two AND terms, then OR the carry terms.
- Test all eight A/B/Cin combinations against the full-adder truth table.
- Read Cout:Sum as 0, 1, or 2 for the three input bits.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
Outputs satisfy Sum=A XOR B XOR Cin and Cout=(A AND B) OR (Cin AND (A XOR B)).
Troubleshooting
- Carry wrong for 1+1+1: trace both AND terms and final OR.
- Inputs float: add a pull-down for each switch.
- IC warms: disconnect power and check for shorts.
Safety and limitations
Logic trainer only; use 5 V and low LED current, not as a machinery control.
Manufacturer and platform documentation
Community Notes for This Project
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