The Arduino Adder Unit was made in October 2021 during PLTW Digital Electronics class. The user inputs a valid expression into the Arduino serial monitor, where the Arduino outputs the expected result in a 4-bit system. At the same time, it loads the binary data of the operands onto a shift register, which from there the physical result is calculated using combinational logic circuitry.

The circuit is essentially the work of YouTube user Ben Eater, with both the D flip-flop shift register and combinational logic circuitry derived from his implementations. These are basic digital logic topics I would later formally learn in university, but Eater made them accessible to anyone interested in electronics.

The Arduino code is entirely my own work. Originally written in October 2021, and revisited in March 2023 for cleaning and bug fixing, the program's job is strictly to translate human input into digital signals, and to verify the circuit results.

Build the circuit described by the schematic in arduino_adder_kicad/arduino_adder_kicad.pdf.

Clone the repository using

git clone https://github.com/WGeckle80/arduino-adder-unit.git

Open arduino-adder-unit.ino in the Arduino IDE, and upload the sketch to your Arduino of choice. Open the serial monitor in the IDE. You should see the following message:

Enter a valid binary operation with a and b in [-8, 7]:
"a + b", "a - b"

Type in a valid expression such as -8 - 7, and take note of the output. Since the arithmetic system is 4 bits, the serial monitor should display -8-7=1, with the corresponding physical output being 0001.

Ben Eater. (2016). ALU Design. https://www.youtube.com/watch?v=mOVOS9AjgFs&ab_channel=BenEater

Ben Eater. (2017). Build an Arduino EEPROM programmer. https://www.youtube.com/watch?v=K88pgWhEb1M&ab_channel=BenEater

Ben Eater. (2015). Learn how computers add numbers and build a 4 bit adder circuit. https://www.youtube.com/watch?v=wvJc9CZcvBc&ab_channel=BenEater

Ben Eater. (2016). Twos Complement: Negative numbers in binary. https://www.youtube.com/watch?v=4qH4unVtJkE&ab_channel=BenEater