The original RCA COSMAC ELF computer appeared on the front cover of Popular Electronics in August, 1976. It was a single board machine based on the RCA 1802 CPU that cost under $100 to build from a bare board. Another $20 would get you a B&W video display. It was an outstanding value that lingered in the classified section of computer magazines like BYTE well into the early 1980s.
Lee Hart's tiny 1802 Membership Card is an incredibly simple computer built around the classic RCA 1802 chip. The dual board design is small enough to cram into an Altoids tin and includes a front panel with 9 blinky LEDs and 11 subminiature toggle switches. A 25-pin parallel port is also built in.
The system is as simple as it looks. The 1802 CPU is driven by an adjustable RC clock oscillator, and a 28-pin IC socket accepts a 2 to 32 Kilobyte RAM or EPROM chip. There's an 8-bit output port, along with an 8-bit input port and an expansion header. The system operates from a 3V-6V power supply and draws less than 1 mA.