We made the extensions port in order to develop additional accessories for Hummingbird Bit that do not fit into the standard LEDs, Sensors, or Servos categories. No such accessories have yet been released, though we do have some under development.
For now, you can hack the extensions port to provide access to the micro:bit’s I2C (Pin 19/20), as well as micro:bit pin 1, battery power, and ground. To get access to these pins, take an RJ-12 6p6c cable and plug it in; we recommend a short 1 foot cable to minimize noise and power drop. Plug the other end into an RJ-12 breakout board. The pin mapping is as follows:
1 - Not connected
2 - Micro:bit Pin 1
3 - GND
4 - Battery Pack Voltage
5 - I2C SDA (Micro:bit Pin 20)
6 - I2C SCL (Micro:bit Pin 19)
Please note that a voltage divider exists on the Hummingbird Bit before the signal reaches Pin 1 of the micro:bit - the signal’s voltage is divided by a factor of 2.5 via a 1.5k and 1k resistor in a voltage divider configuration.
There is a polyfuse on the Hummingbird Bit that prevents the total current draw of all components (servos, LEDs, etc) attached to the board from exceeding two amps. As such, ensure any extensions you attach draw less than one amp to prevent browning out the controller.