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Puck.js v2 is an open-source Bluetooth LE button and beacon powered by the Espruino JavaScript interpreter. Program and debug it wirelessly from any modern b...

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Puck.js v2 is an open-source Bluetooth LE button and beacon powered by the Espruino JavaScript interpreter. Program and debug it wirelessly from any modern browser using Web Bluetooth — no wires, drivers, or native software required. Built around the nRF52832 SoC, it packs sensors, LEDs, an IR transmitter, and GPIO into a compact puck form factor.

Version 2 adds an accelerometer, gyroscope, MOSFET output, calibrated temperature sensor, and improved Bluetooth signal strength over the original Puck.js.

Key Features

  • Wireless JavaScript Programming – Upload, debug, and modify code over Bluetooth from any Web Bluetooth-compatible browser
  • Bluetooth LE – Acts as a beacon (Eddystone/iBeacon), HID keyboard, or BLE central device
  • Built-In SensorsMagnetometer, accelerometer, gyroscope, calibrated temperature sensor, light sensor, and capacitive touch
  • IR Transmitter – Control infrared devices directly from the Puck
  • RGB LEDs – Red, green, and blue LEDs for visual feedback
  • Programmable NFC Tag – Configurable from JavaScript
  • MOSFET Output – Drive external loads directly (v2 addition)
  • Tactile Button – The entire puck acts as a single large button
  • Autonomous Operation – Responds to button presses, magnetic fields, or nearby Bluetooth devices without a phone or hub
  • Open Source – Both hardware and software are fully open source

Specifications

  • SoC – nRF52832 (64 MHz ARM Cortex-M4)
  • RAM – 64 KB
  • Flash – 512 KB
  • Firmware – Espruino JavaScript interpreter (pre-installed)
  • Connectivity – Bluetooth Low Energy
  • Magnetometer – LIS3MDLTR
  • Accelerometer / Gyroscope – LSM6DS3TR-C
  • Temperature Sensor – PCT2075TP (calibrated)
  • GPIO – 7× on 2.54 mm (0.1″) pitch header + 2× SMD pads
  • InterfacesPWM, analogue input, I²C, SPI, Serial, capacitive sensing
  • MOSFET Output – 1×
  • Power – CR2032 coin cell (approximately one year battery life)
  • Case Dimensions – 36 mm diameter × 12.5 mm thick
  • PCB Dimensions – 29 mm diameter × 9 mm thick
  • Weight – 14 g (in case)

Ideal For

  • Bluetooth beacons and proximity sensing
  • Smart home control and IR remote replacement
  • HID keyboard and multimedia triggers
  • IoT prototyping with JavaScript
  • Wearable and portable Bluetooth projects

Package Contents

  • 1× Puck.js v2 in ABS plastic case with silicone cover
  • 1× CR2032 battery (pre-installed)

Resources

Jargon buster

Plain-language definitions for the technical terms used above.

ARM Cortex-M4
The ARM Cortex-M4 is a 32-bit processor core widely used inside microcontrollers, often with hardware support for signal-processing and control tasks. It provides enough processing power to run embedded programs that handle sensors, wireless communication, audio and similar workloads.
BLE
BLE stands for Bluetooth Low Energy, a Bluetooth mode designed for low power use and broad compatibility with modern phones and computers. It connects well to battery-powered and mobile devices, including Apple hardware, though it behaves differently from Bluetooth Classic and its serial-style profiles.
capacitive sensing
Capacitive sensing detects changes in electrical capacitance caused by a nearby object or material, such as a finger, water, or moisture in soil. It is used for touch buttons, proximity detection, and liquid or moisture-level sensing, and it matters because it can work without exposed metal contacts, avoiding the corrosion that bare probes suffer in damp conditions.
Eddystone
Eddystone is a Bluetooth beacon format originally defined by Google for broadcasting identifiers or small pieces of data. Support for Eddystone matters if your project needs to work with software or receivers that expect that beacon format.
GPIO
General-purpose input/output pins are microcontroller pins you can set in software to read signals, switch devices on and off, or connect to peripherals. The number of GPIO pins matters because it limits how many buttons, LEDs, sensors, and other parts you can wire directly to the board.
Gyroscope
A gyroscope measures rotation, such as how fast a board is turning around its X, Y, and Z axes. This matters for projects like gesture controls, balancing robots, and motion tracking where tilt or rotation changes need to be detected.
HID
Human Interface Device is a USB device class used for keyboards, mice, gamepads and similar controls. If a board supports HID over USB, it can act like an input device to a computer without needing a custom driver.
iBeacon
iBeacon is Apple’s Bluetooth beacon format for broadcasting an identifier that nearby devices can recognise. Support for iBeacon matters when building proximity or location projects that need compatibility with apps or systems using that format.
IoT
Short for Internet of Things, meaning physical devices that connect to networks or the internet to send data or be controlled remotely. It matters if you want projects such as connected sensors, remote controls or classroom data-logging activities.
magnetometer
A sensor that measures magnetic fields, often used to work out compass direction. It matters because nearby magnets, motors, or metal objects can affect readings and may require calibration.
PCB
A printed circuit board (PCB) is a board, usually rigid, with etched copper tracks that connect electronic components together without loose wiring. Components are mounted on the board and signals route between them through the copper layout.
PWM
Pulse Width Modulation is a way for a digital pin to simulate variable output power by switching on and off very quickly. It matters for controlling things like LED brightness, motor speed, or servo-style signals from a microcontroller pin.
RAM
RAM (random-access memory) is fast, temporary memory a device uses for working data while it is running; in its common volatile form, its contents are lost when power is removed. Some devices offer a mode that applies settings to RAM only, which is handy for testing changes temporarily because they are not stored permanently and disappear at power-off.
RGB
Short for red, green and blue, the three primary colours of light that are mixed in varying amounts to make a wide range of colours. In electronics RGB can refer to an LED or pixel that blends these three colours, or to a colour signal or interface that carries separate red, green and blue channels.
SMD
SMD means surface-mount device, a component style designed to be soldered directly onto the surface of a circuit board rather than through holes. SMD parts are compact and mounted flat on the board, which suits smaller and mass-produced designs.
SPI
A fast serial communication bus often used for displays, memory cards, and sensors. It matters because SPI devices need specific pins for clock and data, plus a separate chip-select line for each device.
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