The Blinking Computer

An educational computer you can watch think. It is built from discrete transistors, diodes, resistors and LEDs, with no integrated circuits in the processor. Nearly every transistor has an LED on its collector, so the whole state of the machine is visible: the registers, the bus, the arithmetic unit and the phase of the instruction being executed.

A Raspberry Pi Pico 2 provides the memory and the clock. Because the Pico makes every timing edge, the machine runs correctly at any speed from one phase every hundred seconds up to tens of kilohertz. A class can step through a single instruction one phase at a time and see exactly what moves where, or let a program run.

• 16-bit words, 64K words of memory, four registers, sixteen instructions.
• About 800 transistors.
• A Forth-like language, an assembler and an emulator exist for the instruction set, with 247 passing tests. They will be published alongside the hardware design.

Documents

• Design, 2026: the architecture, the storage cell, the bus to the Pico, the instruction set, the phase sequence and the transistor budget.
• References: every outside source cited during the design, with the conversation each came from.
• Design conversations: the discussion that produced the design, kept because the reasons for each decision, and the roads not taken, matter to anyone who wants to copy or change it.