A Bluetooth Keyboard With Exactly One Key—and a Surprisingly Elaborate Settings UI
One Key: Single Button Bluetooth Keyboard
Adafruit's John Park built One Key, a wireless mechanical keyboard containing exactly one key. It connects as a Bluetooth HID device and can act as a mute button, presentation clicker, macro launcher or other configurable control.
Despite having only one physical key, it can send characters, combinations such as Ctrl-Z, strings and media commands. A WebSerial interface also configures LED colors and sleep behavior. The input hardware has been reduced to almost nothing, while the configuration for deciding what that one button means has become impressively rich.
The keyboard has been reduced to one key, but the settings for deciding what that one key does keep multiplying.