MDBT42Q Bluetooth Module

Raytac MDBT42Q

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The MDBT42Q is the Bluetooth module that we use in Puck.js and Pixl.js devices. You can get it with Espruino installed in two forms:

Just got your MDBT42Q? Take a look here!

Note: We only provide support for MDBT42 modules purchased from us. Other modules don't have a bootloader installed and will need connecting to a programmer tool to have firmware installed.



  • Bluetooth Low Energy
  • Espruino JavaScript interpreter pre-installed
  • nRF52832 SoC - 64MHz ARM Cortex M4, 64kB RAM, 512kB Flash
  • 32 x GPIO (capable of PWM, SPI, I2C, UART) on 0.7mm Pitch, including 8 analog inputs
  • 1.7v - 3.6v voltage range (on bare module)
  • Built in thermometer
  • NFC tag programmable from JavaScript (when an antenna is connected)
  • Dimensions: 16mm x 10mm x 2.2mm thick

Breakout board features

  • 2.5 - 16v voltage input (on breakout board), 20uA power draw when advertising
  • 0.1" pin header (With 22 GPIO, 7 analog inputs)
  • Red and Green LEDs
  • Button

Getting Started

Check out the section below on Powering - the bare MDBT42Q module and the breakout have slightly different requirements.

Once powered up follow the Getting Started Guide for details on getting the IDE connected wirelessly. You can also use a wired connection if you prefer.

Powering MDBT42Q

Breakout board

Apply power between any V+/Vin and GND pins. Any voltage between 2.5 and 16 volts will work - just be careful not to get the polarity wrong! Check the pinout below for more information on the location of pins.

Just between Vin/GND and D9/D10 on the bottom edge of the board in the pinout there are two 2mm-spaced pins. These can be used to fit a JST PHR-2 battery connector as mentioned on the Battery page - these are very common for LiPo batteries, which are a good fit for the module.

Bare Module

All you need to get the MDBT42Q working is to apply power between the VDD and GND pins. A 3v non-rechargeable lithium cell is ideal for this (LiPo batteries have a voltage that is too high and will need the voltage dropping with a diode or voltage regulator). Check the pinout below for details on where to connect power.

It is recommended to connect all the GND pins together (especially when designing a PCB) but it is not absolutely required - you can boot the MDBT42Q module with just two wires.

Power Consumption

  • No advertising - 5uA
  • Advertising - 80uA
  • Connected via BLE - 900uA (idle 40uA)
  • LED1 on - 10mA
  • 100% CPU usage running JavaScript - 8mA
  • Using NRF.findDevices to scan for devices - 12mA

On-board peripherals

While there are no buttons or LEDs on the bare module, the MDBT42Q build assumes the following (which are connected on the breakout board):

  • There is a button (BTN/BTN1) between pin D0 and 3.3v. Pulling this high on boot enables the bootloader.
  • There is a LED (LED/LED1) between pin D1 and GND. This is flashes at boot and also indicates bootloader mode.

The breakout board also contains a green LED (LED2) on pin D2 (Espruino 1v99 and earlier require global.LED2=D2 to use this). Since D2 is an analog input it is possible to detect ambient light using analogRead(LED2) - values range from around 0 (dark) to 0.25 (bright).

Hard Reset

Occasionally you may manage to save code to your MDBT42Q that then runs at boot and stops you connecting to it, effectively 'bricking' it.

Recovering it easy:

  • Follow the step for a firmware update, but leave BTN/D0 pressed/connected for 5 seconds (or until the LED goes out).
  • Espruino will now have booted without loading any saved code, however the code will still be there and the next time you reset it the code will be loaded as normal.
  • You can now connect normally with the IDE and continue.
  • To reset completely, type reset(true) into the REPL. This will remove any saved code that is present in the MDBT42Q so even after a reset, your code will not be loaded.


First, it's best to check out the Getting Started Guide

Tutorials using MDBT42Q:

Tutorials using Bluetooth LE:

Tutorials using Bluetooth LE and functionality that may not be part of the MDBT42Q module:


Hover the mouse over a pin function for more information. Clicking in a function will tell you how to use it in Espruino.

  • Purple boxes show pins that are used for other functionality on the board. You should avoid using these unless you know that the marked device is not used.
  • ! boxes contain extra information about the pin. Hover your mouse over them to see it.
  • 3.3v boxes mark pins that are not 5v tolerant (they only take inputs from 0 - 3.3v, not 0 - 5v).
  • 3.3 is a 3.3v output from the on-board Voltage regulator.
  • GND is ground (0v).
  • ADC is an Analog to Digital Converter (for reading analog voltages)
  • USART is a 2 wire peripheral for Serial Data.

MDBT42Q module

3.3v D25
3.3v D26
3.3v D27
ADC 3.3v D28
ADC 3.3v D29
ADC 3.3v D30
ADC 3.3v D31
3.3v D24
3.3v ! D23
D0 3.3v BTN1
D1 3.3v LED1
D2 3.3v ADC LED2
D3 3.3v ADC
D4 3.3v ADC
D5 3.3v ADC
D6 3.3v USART1 TX
D7 3.3v
D8 3.3v USART1 RX
D9 3.3v NFC
D10 3.3v NFC

MDBT42Q breakout board

3.3v D25
3.3v D26
3.3v D27
ADC 3.3v D28
ADC 3.3v D29
ADC 3.3v D30
ADC 3.3v D31
ADC 3.3v D3
ADC 3.3v D4
ADC 3.3v D5
3.3v D11
D6 3.3v ! USART1 TX
D8 3.3v ! USART1 RX
D7 3.3v
D9 3.3v NFC
D10 3.3v NFC

Note: The nRF52 port has one available I2C, SPI and USART (and infinite software SPI and I2C). Unlike STM32-based Espruino boards, these peripherals can be used on any pin.

The bare MDBT42Q module must be powered with a voltage between 1.7v and 3.6v. You can not connect a LiPo battery to it without a voltage regulator. However the breakout board contains a regulator that will work off of 2.5 to 16 volts.


MDBT42Q library


Serial Console

When power is first applied, the MDBT42Q checks if pin D8 (labelled RX on the breakout board) is at 3.3v (which will be the case if it is connected to a Serial port's transmit line). If it is, it initialises the on-chip UART on D8 (MDBT42Q RX) and D6 (MDBT42Q TX) and puts the Espruino console (REPL) on it at 9600 baud.

To use it, connect to a 3.3v output USB to TTL converter as follows:

MDBT42Q USB->TTL converter
D8 (RX) TX ( <- PC )
D6 (TX) RX ( -> PC )
3V 3.3v (Optional - to run without a battery)

You can now use the normal Espruino Web IDE, or a serial terminal application at 9600 baud.

When you connect via Bluetooth, the console will automatically move over. To stop this, execute Serial1.setConsole(true) to force the console to stay on Serial1.

Note: Serial1 is not enabled by default because it requires the high speed oscillator to stay on, which increases power draw a huge amount. If you connect the UART but don't power down and power on the MDBT42Q, you won't get a serial port.

Firmware Updates

Please see the Firmware Update page for detailed instructions.

Note: If you hold BTN (or leave D0 connected to VDD) for too long (> 3 sec), the MDBT42 will leave bootloader mode and will instead start Espruino without loading saved code, allowing a hard reset to be performed.

Other Official Espruino Boards

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