Full Adder From Discrete Transistors

Multisim
2N2222 Transistors
DIP Switches
LEDs

What I Built

A full adder made only from 2N2222 transistors, with no logic ICs. Inputs come from DIP switches, with LEDs as input indicators. The sum and carry outputs show on LEDs as the binary result. I wired it with a very large number of jumper wires and transistors.

Process

I first designed and simulated the whole circuit in Multisim, then built the physical version. It was physically built and works as described.

Circuit Design

This is the circuit I designed and simulated in Multisim. Select an image to open it full size.

Multisim schematic of the full adder. Inputs A, B and Cin each come from a switch. Five gate blocks, HB1 to HB5, are wired together, ending in two LEDs. — The full adder in Multisim. Inputs A, B and Cin feed five gate blocks: HB1 and HB2 are XOR gates, HB3 and HB4 are AND gates, and HB5 is an OR gate. HB2 drives the sum LED and HB5 drives the carry LED.

Transistor-level schematic of the XOR gate block, with inputs IO1 and IO2, six transistors, 220 kilohm and 47 kilohm resistors, and output IO3. — Inside the XOR gate block (HB1 and HB2): transistors and resistors.

Transistor-level schematic of the AND gate block, with inputs IO1 and IO2, three transistors, 220 kilohm and 47 kilohm resistors, and output IO3. — Inside the AND gate block (HB3 and HB4).

Transistor-level schematic of the OR gate block, with inputs IO1 and IO2, three transistors, 220 kilohm and 47 kilohm resistors, and output IO3. — Inside the OR gate block (HB5).