The Heathkit ET-3400 (often called the ET-3400 Microcomputer Learning System or Trainer), introduced in 1977, was a popular educational microprocessor trainer kit. Designed for teaching 6800 assembly language, digital logic, and interfacing, it was widely used in schools, universities, and by hobbyists learning the fundamentals of microprocessors in the late 1970s and 1980s.
Heathkit, famous for DIY electronics kits, developed the ET-3400 to capitalize on the microprocessor boom. It was based on the Motorola 6800 CPU, with design focusing on hands-on learning. Later variants (ET-3400A) updated to 6808/6802 CPUs. Heathkit also offered accessory boards and structured courses (e.g., EE-3401 Microprocessors) to complement the trainer.
Released around 1977 as a kit (~$130 assembled higher), the ET-3400 was marketed through Heathkit catalogs and electronics magazines. It sold thousands of units, remaining available into the 1980s. An optional ETA-3400 Memory/I/O Accessory added RAM, ROM (Tiny BASIC), serial port, and cassette interface, turning it into a basic computer.
The ET-3400 centered on the Motorola MC6800 microprocessor. Key features included:
Compact blue plastic case with front-panel controls—no keyboard or video output standard.
The built-in 1 KB ROM monitor allowed hex entry, memory examination, execution, and single-step debugging. Users hand-entered 6800 machine code or assembly via keypad. With ETA-3400 accessory: Tiny BASIC, serial terminal support, cassette save/load. Heathkit courses included experiments in interfacing LEDs, switches, DACs, and more on the breadboard.
The ET-3400 democratized microprocessor education, teaching thousands the inner workings of CPUs before affordable personal computers. Its trainer design influenced later educational tools. While basic compared to full systems, its interactivity made concepts tangible. Surviving units are collectible, with modern expansions (e.g., RAM upgrades, Raspberry Pi interfaces) and emulators keeping it alive. The ET-3400 symbolizes Heathkit's educational legacy in the microprocessor revolution.