Edge Connector & micro:bit pinout

The edge connector provides a set of pads and pins to allow interfacing to other circuits and components.

Overview

The edge connector on the micro:bit is used to connect to external circuits and components.

There are 25 strips/pins including 5 rings for using with 4mm banana plugs or crocodile clips. 3 of these rings are for general purpose input and output (GPIO) and are also capable of analog, PWM and touch sensing, and two are connected to the micro:bit power supply.

The smaller strips spaced at 1.27mm on the edge connector have additional signals, some of which are used by the micro:bit, and others that are free for you to use. There are a number of external PCB connectors for purchase with an 80w 1.27mm pitch that can be used to easily access these extra pins.

Only the pins on the front are connected to signals. The back rings are connected to the front rings, but the back small strips are unconnected.

Edge Connector Pins

edge connector

Also checkout microbit.pinout.xyz for more information.

Pins and Signals

This table shows various data about each of the pins on the micro:bit edge connector.

m:b ring mod schem MCU s/w functions dir pull?
  21 COL1R P0.04 P3 (GPIO), (ANALOG), LEDCOL(1), (PWM), (UART) O
    PAD1   P0 }    
    PAD1   P0 }    
0 18 PAD1 P0.03 P0 } GPIO, ANALOG, TOUCH, PWM, UART I e10Mu, i12Kd
    PAD1   P0 }    
  22 COL2R P0.05 P4 (GPIO), (ANALOG), LEDCOL(2), (PWM), (UART) O
  37 BTN_A P0.17 P5 (GPIO), BUTTON(A), (PWM), (UART) I e10Ku, i12Kd?
  30 COL9R P0.12 P6 (GPIO), LEDCOL(9), (PWM), (UART) O
  29 COL8R P0.11 P7 (GPIO), LEDCOL(8), (PWM), (UART) O
    PAD2   P1 }    
    PAD2   P1 }    
1 19 PAD2 P0.02 P1 } GPIO, ANALOG, TOUCH, PWM, UART I e10Mu, i12Kd
    PAD2   P1 }    
  38 P0.18 P0.18 P8 GPIO, PWM, UART I i12Kd
  28 COL7R P0.10 P9 (GPIO), LEDCOL(7), (PWM), (UART) O
  23 COL3R P0.06 P10 (GPIO), LEDCOL(3), (ANALOG), (PWM), (UART) O
  9 BTN_B P0.26 P11 (GPIO), BUTTON(B), (PWM), (UART) I e10Ku, i12Kd?
  40 P0.20 P0.20 P12 (GPIO),ACCESSIBILITY, (PWM), (UART) I i12Kd
    PAD3   P2 }    
    PAD3   P2 }    
2 20 PAD3 P0.01 P2 } GPIO, ANALOG, TOUCH, PWM, UART I e10Mu, i12Kd
    PAD3   P2 }    
  6 SCK P0.23 P13 GPIO, SPI(SCLK), PWM, UART I i12Kd
  5 MISO P0.22 P14 GPIO, SPI(MISO), PWM, UART I i12Kd
  4 MOSI P0.21 P15 GPIO, SPI(MOSI), PWM, UART I i12Kd
  34 P0.16 P0.16 P16 GPIO, PWM, UART I i12Kd
    +V_TGT     PSU(V_TGT)  
    +V_TGT     }  
    +V_TGT     }  
3V   +V_TGT     } PSU(V_TGT)  
    +V_TGT     }  
    +V_TGT     PSU(V_TGT)  
  17 SCL P0.00 P19 (GPIO), I2C(SCL), (PWM), (UART) O e4k7u
  16 SDA P0.30 P20 (GPIO), I2C(SDA), (PWM), (UART) I e4k7u
    GND     PSU(GND)  
    GND     }  
    GND     }  
GND   GND     } PSU(GND)  
    GND     }  
    GND     PSU(GND)  
column purpose
m:b ring the micro:bit basic interface (the 5 rings on the front)
mod the pin number on the module:bit
schem the symbol name in the micro:bit schematics
MCU the actual pin name of the nRF51822 MCU chip
s/w the name that is used in the DAL runtime software
functions all possible functions, BOLD for default. brackets indicate use with caution
dir the startup conditions (direction) when the micro:bit boots: Input or Output
pull? pull up or down resistors. e10Mu means an external 10Mohm pullup, i12Kd means an internal 12K pull down.

Notes

  1. RINGs for 0, 1, 2, 3V and GND are also connected to the respective reverse side rings on the edge connector.

  2. The 3V and GND rings have guard strips either side of the big rings, to avoid any degradation of device performance due to slipping crocodile clip connections. Care should be taken on rings 0, 1 and 2 to avoid shorting crocodile clips against adjacent pins, which could cause some slight interference with the pattern currently displayed on the LED matrix, or introduce some innaccuracies in the light sensing readings.

  3. The DAL DynamicPWM driver (and the underlying nrF51 timer peripherals) dictate that PWM can only be active on 3 pins simultaneously. Any attempt to allocate a 4th pin for PWM use, will disable one of the existing PWM pins.

  4. Digital input pins are by default configured with internal pull down resistors when the pins are configured by the DAL.

  5. Functions in brackets should be used with caution, as other features of the device may become unstable, degraded or non operational, if their normal use is not disabled in the software first.

  6. The source file for the pinout table is held in CSV format. You can load this into a spreadsheet and sort and filter it in any way that makes sense to you. There is also a zipped Python script in this folder that you can download to re-generate the markdown table version of the pinmap used on this page, from the .csv file.

  7. The pin marked ‘ACCESSIBILITY’ is used to enable/disable an on-board accessibility mode, and should not be used for anything else (even though it can be used as a GPIO for testing). Future versions of the official micro:bit editors may remove the ability to write to this pin.

Uncoupling Default Functionality

Pins that are marked with brackets around functions, require the default functionality for that pin to be disabled, before other functions can be used.

pins: P3, P4, P6, P7, P9, P10

These pins are coupled to the LED matrix display, and also it’s associated ambient light sensing mode. To disable the display driver feature (which will automatically disable the light sensing feature) call the DAL function display.enable(false). To turn the display driver back on again later, call the DAL function display.enable(true).

Note also that the LED 3x9 matrix connects LEDs with associated resistors across these pins, so you should take that into account when designing circuits to use these pins for other purposes.

pins: P5, P11

These pins are assigned to the two on-board buttons. In their default setup with all the standard high level languages, there is a global uBit instance containing: uBit.buttonA, uBit.buttonB and uBit.buttonAB.

Buttons are hooked into the system timer in their constructor for regular debouncing. However, if you want to completely remove this feature and use the physical pins for other purposes, you can delete uBit.buttonA, it will call the C++ destructor and de-register the button instance from the system timer, effectively disabling all DAL activity with that pin. It is then possible to use a MicroBitPin instance around the physical pin name to control it directly without interference from the DAL.

Be aware though, that there are 10K external pullup resistors fitted to the micro:bit board.

pins: P19, P20

These pins are allocated to the I2C bus, which is used by both the onboard motion sensor. It is strongly suggested that you avoid using these pins for any function other than I2C.

It is possible to disable the DAL services that use these pins as the I2C bus, but the motion sensor device will still be connected to the bus, and may try to interpret the signals as data payloads, which could create some undesirable side effects on the SDA and interrupt pins. There are 4K7 pullups fitted to both pins on the board, so the best use for these two signals is to add other I2C devices.

The main reason you might choose to use these pins for other purposes would be if you were designing your own micro:bit variant without any I2C devices, and then it would free up two more pins for other purposes.

Power Supply Capabilities

The power supply capabilities and parameters, which better define how you can use the GND and 3V rings, are detailed here: psu

GPIO Capabilities

These key GPIO parameters are transcribed directly from Section 6, 7 and 8 of the nRF51822 Datasheet, and provided here as a handy reference.

KEY Description section Min Max
VOL Voltage Output Low 8.23 VSS 0.3V
VOH Voltage Output High 8.23 VDD-0.3 VDD
VIL Input voltage for logic low 8.23 VSS 0.3*VDD
VIH Input voltage for logic high 8.23 0.7*VDD VDD
xxx Max source current from IO pin 8.23 5mA
xxx Max sink current into IO pin 8.23 5mA
VIO Tolerable pin voltages for IO pin 6 -0.3V VDD+0.3
xxx Pin impedance when an input ? TBD  
VDD(o) Operating voltage range (LDO) 7 1.8V 3.6V
VDD(a) Absolute voltage range 6 -0.3V +3.9V
VSS Ground reference 6 0V 0V
RPU Pull up resistance 8.23 11K 16K
RPD Pull down resistance 8.23 11K 16K

NOTE 1: The maximum number of pins configured as high-drive (5mA) at any one time is 3 pins.

NOTE 2: A common way that the maximum pin voltages can be exceeded, is to attach an inductive load such as a speaker, motor, or piezo sounder directly to the pin. These devices often have significant back-EMF when energised, and will generate voltages that exceed the maximum specifications of the GPIO pins, and may cause premature device failure.

NOTE 3: The pin marked ‘ACCESSIBILITY’ is used to enable/disable an on-board accessibility mode, and should not be used for anything else (even though it can be used as a GPIO for testing). Future versions of the official micro:bit editors may remove the ability to write to this pin.

NOTE 4: The BBC suggest in the safety guide, that the maximum current you can draw from the whole edge connector at any one time is 90mA. This is set based on the 30mA budget for on board peripherals, and the fact that the on board regulator of the KL26 when powered from USB is rated at a maximum of 120mA.

PCB Connector

The PCB connector is an 80 way * 1.27mm pitch double sided connector.

You can buy this connector from a number of sources.

At a pinch, it is also possible to use an old PCI edge connector from a PC motherboard, as the pitch is the same (but it is slightly wider).

There is a good mechanical data-sheet for the right angle PCB edge connector available from Cool Components.

Can You Find a Better Connector?

There are a number of suppliers of edge connector for the micro:bit, in various forms, such as a right angle through-hole, a stand-up through-hole and a stand-up surface mount. There are a wide range of connector manufacturers that sell thousands of different types of connectors.

There are also some nice ideas that have surfaced in the community such as using just the right size of countersunk or cheese-head bolt, or even 3D printed inserts.

Can you help to find or design a better connection solution to the micro:bit edge connector? Share your designs and discoveries with us!

Third Party Connnectors

Add your connector to our list

Supplier Product
Cyclonn Cylconn 90 degree connector, Cylconn 180 degree connector

Further information

micro:bit schematics

micro:bit CAD resources (Kitronik)

Edge connector CAD resources (Proto-Pic)

Eagle libraries for the micro:bit edge connector

KiCad component and footprint library

2D CAD drawing This drawing has all the key micro:bit dimensions, including the pin spacing of the various pins of the edge connector on the micro:bit board.

STP file This file is a 3D CAD file for use with 3D modelling software.

STL file This file can be used with 3D printers.

SAT file This file can be used with ACIS Modeller.