Description Chain Key is a single-button input node in the M5Stack Chain series. It combines a hot-swappable mechanical blue switch, programmable RGB feedback and an STM32G031G8U6 core MCU in a compact Chain-series control module. Chain Key uses UART serial cascading communication, making it suitable for interactive button controls, smart home actions and human-machine interfaces. With two HY2.0-4P expansion interfaces, Chain Key can be connected with more Chain series devices to build larger interactive systems. Features Single-button Chain input: Chain Key provides one tactile button node for M5Stack Chain-series projects. Hot-swappable blue switch: the mechanical keyboard switch design gives Chain Key clear tactile feedback and easy switch replacement. STM32G031G8U6 MCU: an integrated STM32G031G8U6 controller handles key input, RGB output and Chain communication. Programmable RGB feedback: two WS2812C RGB LEDs let Chain Key show status, alerts and interactive lighting effects. UART cascading protocol: Chain Key communicates through UART at 115200bps@8N1 for Chain-series expansion. Dual HY2.0-4P connectors: two expansion interfaces help connect Chain Key with Chain Bridge, Chain DualKey and other Chain devices. Compact control node: the 23.9 x 23.9 x 34.4mm body fits small smart home panels, control boxes and desktop interaction projects. Specifications MCU STM32G031G8U6 Input Power DC 5V Communication Method UART 115200bps@8N1 Interface Spec 2 x HY2.0-4P RGB LED 2 x WS2812C Working Power Consumption 28.24mA Working Temperature 0 ~ 40°C Product Size 23.9 x 23.9 x 34.4mm Product Weight 9.1g Package Size 138.0 x 93.0 x 26.0mm Gross Weight 14.4g Applications Smart home scene triggers and programmable wall-button projects using Chain Key. Human-machine interaction panels that need tactile input plus RGB status feedback. Desktop control buttons, macro controls and quick-action input devices. Chain-series interactive installations with multiple cascaded input modules. Education and prototyping projects that demonstrate UART cascading and button-event handling. Product List 1 x Chain Key 1 x Chain Bridge 1 x Keycap Sticker Other Content Chain Connection Direction When using the Chain Bridge connector, connect the main controller Chain DualKey with Chain Key and other Chain series input devices in the correct direction. The triangle arrow should point outward from the Chain DualKey controller. Communication And Expansion Chain Interface Two HY2.0-4P connectors provide input and output chaining for Chain Key. Serial Settings UART communication uses 115200bps@8N1. Controller Pairing Use Chain Bridge with Chain DualKey to connect Chain Key into a Chain-series setup. Development Resources Arduino quick start, M5Chain library, example program, UiFlow2 documentation, firmware and protocol files are listed in Resources. Resources Chain Key product document Schematic PDF for the button node Model size PDF for the button node Arduino quick start guide for the button node M5Chain Arduino library Arduino example program for key input UiFlow2 documentation for the key module Internal firmware repository for the key module Communication protocol PDF for Chain Key Documentation PDF for the button node FAQ What is Chain Key used for? Chain Key is used as a single-button input node for smart home control, human-machine interaction, quick-action controls and Chain-series interactive projects. Which controller does Chain Key use? Chain Key integrates an STM32G031G8U6 MCU for button input, RGB LED control and UART Chain communication. How does Chain Key communicate? Chain Key uses UART serial cascading communication at 115200bps@8N1. Can Chain Key connect with other Chain devices? Yes. Chain Key has two HY2.0-4P expansion interfaces and can be connected with Chain Bridge, Chain DualKey and other Chain series devices. What is included in the package? The package includes 1 x Chain Key, 1 x Chain Bridge and 1 x Keycap Sticker.
