The M5 Hexadecimal Display
The M5 Hexadecimal Display: A Breadboard-Friendly Hexadecimal Display for Teaching Digital Logic and Programmable Hardware
M5 is developing a small breadboard-friendly printed circuit board designed to make four-bit digital logic immediately visible to students of digital electronics, from middle school through college. The board accepts a four-bit binary input plus power and ground, and displays the corresponding hexadecimal value — 0 1 2 3 4 5 6 7 8 9 A b C d E F — on a single seven-segment LED display. Four small indicator LEDs show the input bits directly, allowing students to see the binary value and its hexadecimal representation at the same time.
The board plugs into the top of a standard solderless breadboard. Along its lower edge are six pins: bit 0, bit 1, bit 2, bit 3, +5 V, and ground. Directly above the four data pins are four tiny LEDs that show the input state. Above those LEDs is the seven-segment display. Above the display is a CPLD that performs the decoding from four-bit input to seven-segment output, with a driver array nearby.
Unlike familiar BCD-to-seven-segment decoder chips used in many introductory electronics labs, this board supports the full hexadecimal range from 0 through F. This matters because students in computer engineering, embedded systems, digital logic, and retrocomputing encounter hexadecimal constantly, yet often lack a simple physical device that lets them “see” a nibble as both binary and hexadecimal.
In the live demonstration, participants will interact with the board in three ways. First, they will manually drive the four data inputs using switches or jumper wires on a breadboard. As the input pattern changes, the four bit LEDs will show the binary value and the seven-segment display will show the corresponding hexadecimal character. Second, the board will be connected to a small four-bit up/down counter, allowing visitors to watch the display count from 0 to F and back again. Third, the demonstration will show the design flow used to create the board, including the schematic and PCB layout in KiCad, the logic equations used to define the seven-segment decoder, and the process of programming the CPLD using Microchip’s WinCUPL II.
The educational goal is to show how a student can move from a small conceptual need — “I want to see the value of these four bits” — to a finished custom PCB. The board connects binary representation, hexadecimal notation, seven-segment displays, programmable logic, PCB layout, breadboard prototyping, and the transition from abstract Boolean expressions to a working physical artifact.
The use of a CPLD is especially important. Many introductory digital electronics courses rely heavily on fixed-function logic chips, microcontrollers, or software simulation. CPLDs occupy a valuable middle ground: students can express logic directly, synthesize it into hardware, and observe the result without the conceptual overhead of a full FPGA workflow. The Boolean equations for the hexadecimal decoder can be inspected, modified, and reprogrammed, making the board a compact introduction to programmable logic.
This project is well suited to academic makerspaces because it is small, affordable, reproducible, and legible. It can be used as a teaching aid, lab component, debugging tool, outreach object, or KiCad design example. It also demonstrates a makerspace-centered approach to curriculum development: instead of relying only on commercial lab modules, students and instructors can design small custom boards that precisely match local teaching needs.
The contribution of this demonstration is not the invention of hexadecimal notation, seven-segment displays, or programmable logic. Rather, it is the integration of these familiar ideas into a small, teachable artifact. A four-bit hexadecimal display is a small object, but it addresses a real teaching need: helping students connect binary signals, physical circuits, and symbolic representation.
Keywords
Academic makerspaces; digital logic; CPLD; KiCad; PCB design; seven-segment display; hexadecimal; breadboarding; computer engineering education; programmable logic.
by Baird Soules - 9 September 2026