Digital Full Adder
A modular digital full adder built from transistor and NAND-gate implementations.
Overview
I started designing this digital full adder shortly after learning about logic gates. First, I drew a full adder using XOR-gates and AND-gates. Then I replaced the gates with NAND-gates and drew a full adder using nine NAND-gates. After finishing the NAND-gate logic, I designed the circuit with the circuit simulator of HTL Braunau.
The project includes KiCad files, circuit simulator files, and pictures.
How the modules fit together
The full adder combines the input bits A, B, and Cin into the outputs Sum and Cout.
- The transistor module builds the logic from discrete bipolar transistors.
- The NAND-gate module implements the adder with 74HC00 chips.
- The 74HCT283E module uses a dedicated 4-bit binary full adder.
- The Raspberry Pi Pico module implements the logic in Micropython.
- The power supply module provides regulated voltage for the circuit modules.
Module 1: Bipolar transistors
The first module of the full adder is built with bipolar transistors. CircuitSim files, KiCad files, and pictures are available in the Transistors folder.
Materials
- 19x BC547C NPN general purpose amplifier
- 9x resistor (10kOhm)
- 3x resistor (330kOhm)
- 18x resistor (100kOhm)
- 3x LED (5mm, red)
- 3x sliding switch
- Copper wire
- Pin headers (angled, 2-row)
Module 2: NAND Gates (74HC00)
The second module uses NAND-gates. It can be connected to module 1 or directly to the power supply through the pin headers.
Materials
- 3x 74HC00 quadruple 2-input NAND-gates
- 3x resistor (330kOhm)
- 3x LED (5mm, red)
- 2x sliding switch
- Pin headers (angled, 2-row)
Module 3: 4-Bit Binary Full Adder (74HCT283E)
The third module consists of one 4-bit binary full adder.
Materials
- 1x 74HCT283E: 4-bit binary full adder with fast carry
- 3x resistor (330kOhm)
- 3x LED (5mm, red)
- 2x sliding switch
- Pin headers (angled, 2-row)
Module 4: Raspberry Pi Pico (RP2040)
Module number 4 is one Raspberry Pi Pico. The code is written in Micropython. You can find it underneath the materials. Although using a Raspberry Pi for a single module of a full adder is overkill, I still thought that it would be a nice extension.
Materials
- Raspberry Pi Pico (RP2040)
- 3x resistor (330kOhm)
- 3x LED (5mm, red)
- 2x sliding switch
- Pin headers (angled, 2-row)
You can view a simulation of the circuit using this link.
Power supply
Materials
- 1x battery holder
- 1x 9V battery
- 2x capacitor (100nF)
- 2x capacitor (100uF)
- 1x voltage regulator (-5V, MC7905)
- 2x sliding switch
- Pin headers (angled, 2-row)
I did not have a positive voltage regulator (MC7805) at home, so I used the negative one (MC7905).
More modules to come
- FPGA
- MOSFET transistors
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