Serial interface (dev. #03)

The device enables communication between the ZX Spectrum computer, external peripherals, and a PC using the most popular communication interfaces used in automation: UART (RS-232), SPI, I2C, and USB. With this interface, you can connect most devices designed for Arduino to the computer: temperature/pressure/pollution sensors, displays, relays, LEDs, LCD displays, motors, servos, and many, many more…

Currently available on eBay. Go to offer.

One of the device’s highlights is the ability to communicate with it from a simple BASIC terminal.
Manual excerpt.