Why build this?

This project started with a simple question: what would a computer look like if we never agreed that binary was the only sensible choice?

Balanced ternary is an elegant number system with a long history in theoretical computing. Its use was seriously considered in early Soviet computer research (most notably the Setun machine, 1958), and it remains theoretically interesting today.

Instead of bits, balanced ternary uses trits: −, o, or +. The least significant digit represents ±1, the next ±3, the next ±9, and so forth. Numbers are coded as follows:

This makes negation trivially easy (just flip the signs), eliminates the need for a separate sign bit, and keeps arithmetic symmetric around zero. In this project, the three states are represented physically as voltage levels: −5 V, open, and +5 V.

I chose relays and diodes because they are easy to understand and relate to. You can hear them click, watch LEDs change state, and trace every signal path by eye. This is not about speed or efficiency. It is about understanding computation at a fundamental level, exploring an alternative number system, and embracing the constraints — and beauty — of hardware logic. What followed was a long descent into diode matrices, relay logic, and the realization that ternary arithmetic is elegant in theory but not trivial in hardware.

No References, Just Plain Curiosity

All of this was designed completely from scratch. No reference designs, no copied schematics, and no “standard” ternary circuits quietly borrowed from somewhere else. I started with an empty page and worked forward by thinking, prototyping, testing, redesigning, and debugging.

Schematics, logic concepts, PCB layouts, and mechanical assemblies are all original. This project isn’t about efficiency or usefulness; it’s about understanding computation by physically building it, one clicking relay at a time.

The Ternary Relay

The whole project hinges on a deceptively simple trick: building a three‑state switching element from bog‑standard SPDT relays on a single PCB.

This Double‑Pole Triple‑Throw (DPTT) relay is synthesized from two sub‑miniature G6K‑2F‑Y SPDT relays, packaged in a wide 24‑pin DIP configuration. When neither coil is energized, the common pin floats, representing the o (open) state. Energizing the first coil connects the common to −5 V, representing −. Energizing the second coil connects it to +5 V, representing +. Diodes ensure that only the appropriate relay is driven.

Red and blue LEDs indicate positive and negative states, chosen to evoke “warm” (positive) and “cold” (negative) temperatures. This creates a true three‑state switching element that maps directly onto balanced ternary logic; built from parts you can hold in your fingers and hear click.

A Design Challenge

A critical design constraint follows directly from this arrangement: the −5 V and +5 V rails must never be connected to each other through the relay contacts.

Since both supply rails are always present in the circuit, a single wiring error or logic fault that simultaneously activates both coils — or routes both rails to the same common pin — would create a direct short circuit, with the inevitable magic smoke as an unpleasant result. Every stage of the adder, the demultiplexer tree, and the amplifier board was therefore carefully designed to guarantee that at any given moment only one coil per relay module can be driven, and that no signal path can ever bridge the two supply rails.

Clear Stages and LEDs

The adder was designed with an educational purpose in mind. Every stage is named (in Dutch) so that its...