BBC Micro:Bit can be programmed in C using the Arduino IDE and the pinMode/digitalWrite functions. The clock is 16 MHz, AVR328 applications run at ~1/4 of the speed.The inside micro-controller is a nRF51, less than 80mA with BT low energy, 2.5 to 3.3V.Adafruit has a good documentation and has adapted many Arduino libraries. We have documented the pin numbers and how to access the 5x5 Led matrix. If you like working with pins ans inserted files, see www.didel.com/MicrobitArduino.pdf We developed a PCB that is screwed on the Microbit, no connector - available on Tindie (OledForMicrobit)