Having been working on some projects with microbit, I still wants to understand more on the design and layout. This is important for us when we understand more of the pin design, we can connect to make full use of different pins for different project.
On Board Key Features
LEDS
- The LED matrix is physically laid out as a 5×5.
- On the V2 board this is implemented as a 5×5 matrix, but in the V1, this is implemented as a scanned matrix of 9×3.
Interface
- The Interface sheet shows the KL26V1/KL27V2 processor, which is an NXP microcontroller with an Arm processor, that implements the USB protocol for the USB connector.
Sensors
- There is one combined motion sensor IC on the microbit, that contains an accelerometer and a magnetometer.
- The accelerometer measures acceleration in 3 axes, and the magnetometer can be used as a compass, as well as a magnetic field detector.
Power Supply
- Power to the microbit can be provided by 3 sources: The USB, the battery connector, and the 3V pad on the edge connector.
Application Processor
- The main application processor runs both the runtime code and user code, as a single binary image.
- Code is loaded into this processor via the interface processor.
- Communications via USB serial is done via the interface processor.
- All GPIO pins on the edge connector are serviced by this application processor.
- All bluetooth features are provided by a SoftDevice stack loaded into this processor.
- The nRF52V2 features additional NFC functionality on P0.09(NFC1) and P0.10(NFC2) that is disabled by default, but can be configured using the nRF5SDK.
PIN Layout
Large pins
- The first three, labelled 0, 1 and 2 are flexible and can be used for many different things – which means they are often called ‘general purpose input and output’ (shortened to GPIO).
- These three pins also have the ability to read analogue voltages using something called an analogue-to-digital converter (ADC).
- They all have the same function:
- 0: GPIO (general purpose digital input and output) with analogue to digital convertor (ADC).
- 1: GPIO with ADC
- 2: GPIO with ADC
- 3V: 3 volt power output or power input.
- (1) power output: When microbit is plugged by USB or a battery, the 3V pin act as a power output to power circuit;
- (2) power input: 3V pin becomes a power input to power the microbit and microbit is not powered by USB or battery.
- GND: To ground in order to complete a circuit (required when using the 3V pin).
Small pins
There are 20 small pins numbered sequentially from 3-22 (these pins are not labeled on the micro:bit, however, they are labelled in the picture above).
- pin 3: GPIO shared with LED Col 1 of the LED screen; can be used for ADC and digital I/O when the LED screen is turned off.
- pin 4: GPIO shared with LED Col 2 of the LED screen; can be used for ADC and digital I/O when the LED screen is turned off.
- pin 5: GPIO shared with Button A. This lets you trigger or detect a button “A” click externally. This pin has a pull-up resistor, which means that by default it is at voltage of 3V. To replace button A on the micro:bit with an external button, connect one end of the external button to pin 5 and the other end to GND. When the button is pressed, the voltage on pin 5 is pulled down to 0, which generates a button click event.
- pin 6: GPIO shared with LED Col 9 of the LED screen; can be used for digital I/O when the LED screen is turned off.
- pin 7: GPIO shared with LED Col 8 of the LED screen; can be used for digital I/O when the LED screen is turned off.
- pin 8: Dedicated GPIO, for sending and sensing digital signals.
- pin 9: GPIO shared with LED Col 7 of the LED screen; can be used for digital I/O when the LED screen is turned off.
- pin 10: GPIO shared with LED Col 3 of the LED screen; can be used for ADC and digital I/O when the LED screen is turned off.
- pin 11: GPIO shared with Button B. This lets you trigger or detect a button “B” click externally.
- pin 12: this GPIO pin has been reserved to provide support for accessibility.
- pin 13: GPIO that is conventionally used for the serial clock (SCK) signal of the 3-wire Serial Peripheral Interface (SPI) bus.
- pin 14: GPIO that is conventionally used for the Master In Slave Out (MISO) signal of the SPI bus.
- pin 15: GPIO that is conventionally used for the Master Out Slave In (MOSI) signal of the SPI bus.
- pin 16: Dedicated GPIO (conventionally also used for SPI ‘Chip Select’ function).
- pins 17 and 18: these pins are wired to the 3V supply, like the large ‘3V’ pad.
- pins 19 and 20: implement the clock signal (SCL) and data line (SDA) of the I2C bus communication protocol. With I2C, several devices can be connected on the same bus and send/read messages to and from the CPU. Internally, the accelerometer and the compass are connected to i2c.
- pins 21 and 22: these pins are wired to the GND pin and serve no other function
Main Hardware key features on board design to be discussed below are:
Assembly Diagram
Hope you like microbit topic. Take care and stay healthy.
