Creative Inspiration Center micro:bit basic programming guide Input function group (special analysis)3IIIDescription of the power supply system for the micro:bit motherboard
Overview
Micro:Bit motherboards can be powered in a variety of ways, and can be divided into 4 types in total.
1. USB interface power supply.
The USB power supply standard is DC5V, that is, DC 5V voltage. After the DC-DC conversion of the on-board regulator, DC3 is output3V voltage to power the hardware circuitry of each part of the micro:bit system.
2. Use various batteries (lithium batteries) for power supply.
At present, lithium batteries are commonly used in power batteries for electronic products. According to the power supply requirements of the motherboard, we can provide batteries with 3V voltage standard, 5V voltage standard, 6V, 9V, 12V, 15V, 24V and other power supply batteries with different voltage standards. The battery power standard of micro:bit motherboards should not exceed 42v。The power battery is connected via the JST connector terminal block of the micro:bit motherboard (white socket on the motherboard, white plug on the battery end).
3. Use a stable DC regulated power supply to directly supply power to the motherboard.
Connect directly to the micro:bit motherboard through two oval pad contacts on the back and right side of the motherboard33V power supply. The form of connection adopts the method of welding, and the positive and negative poles of the power supply (pay attention to the distinction) are respectively welded on the surface of the oval pad contact, the upper part of the GND contact, and the lower part is the 3V voltage contact.
4. Use the micro:bit motherboard, and the power pin on the external connection port is used for power.
In the absence of any power supply system on the Micro:bit motherboard, the power pins 3V and GND on its external connection ports can be used to provide reverse power to the motherboard.
The reason for this is that the main function and purpose of the power pin on the external connection port is to provide a certain and necessary power ** and reference voltage standard (0V) for the external device when the micro:bit is connected to the external device, so as to facilitate the connection between the devices and the consistent setting of the communication standard.
In other words, the power pins that were originally used for output are connected to serve as the power supply side of the micro:bit motherboard, so it is called reverse power supply. The power pins 3V and GND on the external connection port of the micro:bit are the same as the oval power contacts (pads) in item 3 above in the circuit. They are pad contacts at different locations on the same functional line. As a result, the power pins on the external connection ports have the same function, structure, and application methods as the pad power contacts on the micro:bit motherboard.
In micro:bit motherboards, different power supply forms have different driving and driving capabilities for external devices connected to the board and outside the board. There are many reasons for this, including the driving capacity of the power supply system itself and the limitation of the driving capacity of the motherboard power conditioner circuit.
We take the USB port power supply as an example, assuming that the driving capacity of the external power supply is sufficient, so as to summarize and analyze the power consumption of the Micro:bit motherboard itself and the ability to drive the load on the motherboard, including the driving and distribution of the internal and external components of the board.
The V1 version of the micro:bit motherboard converts the USB DC 5V voltage to DC 3 through the KL26 microcontroller (on-chip voltage conversion device) on the board in the case of USB power supplyAfter 3V, power is supplied to all other hardware units on the micro:bit motherboard. After voltage conversion, the KL26 chip can provide a maximum drive current of 120mA.
In addition to the use and consumption of the internal and external components of the board, the rest is used for the driving tasks of the devices connected to the external connection port. The interior and exterior of the board include LED dot matrix display, Bluetooth, microphone, speakers, and other peripherals such as various sensors.
The power consumption varies from external device to device, assuming that all the internal and external components of the board are in operation, we should estimate the overall maximum operating current to be 30mA, then the drive current left for the external connection port is 90mA (V1 version). The V2 version of the KL26 on-chip power conditioner can provide 300mA of drive current, so it can provide 270mA of drive current on the external connection port.
The KL26 chip is a dedicated chip for USB power supply and other functions. When the micro:bit motherboard is powered by batteries, the KL26 is not powered on or working, so the USB power LED (indicator) will not be lit. This is the main difference between a Micro:Bit motherboard that is powered by USB and battery.
When multiple power systems are loaded on the Micro:bit motherboard hardware system at the same time (USB power supply and battery power supply are used as examples). Not only that, the party with a high output voltage will prevent the other party from supplying power to the motherboard, but the party with the high voltage will also output current in the opposite direction to the low voltage side (reverse power supply). Conflicts between power supply systems can lead to unpredictable consequences and damage.
It is necessary not only to avoid the occurrence of conflicts, but also to ensure the effective function of each power supply system. It has the advantage that when one side of the power supply stops, the other side of the power supply system can form an effective supplement. The solution is to connect a diode to prevent reverse conduction before each power supply system can be connected to the micro:bit motherboard hardware system. When the reverse power supply phenomenon occurs on either side, due to the blocking effect of the forward protection diode, the current input of the power supply system of the other party can be effectively avoided, so as to ensure that the power supply system will not be affected by other power supply systems even if it is not in the power supply state.
Critical voltage parameter standards
The structure of a micro:bit motherboard is a highly integrated computer system built around several core chips, integrated circuits, and their peripheral circuits. Each core chip has different functions, and also has different technical parameter requirements, including working voltage range, maximum and minimum voltage, and maximum acceptable voltage requirements. This is the technical application specification for the power supply of different core chips in the micro:bit motherboard. The specifications of the micro:bit motherboard vary from version to version.
NRF51: It is the main function chip of the system, and all the design and functions of the MCU and Micro:Bit motherboards are carried out around this microcontrol system.
KL26: It is a microcontroller chip, MCU, the main function in the system is the control of various functions of the USB port, such as ** function, USB communication function, and USB power supply voltage conversion function.
LSM303: Compass function chip, also known as electronic compass. It is a sensor system that is built by a combination of an accelerometer and a magnetic sensor. It is a digital sensor. Information is exchanged with the MCU through I2C communication.
MMA8653FC: 3-axis accelerometer, digital sensor. Information is exchanged with the MCU through I2C communication.
MAG3110: 3-axis magnetometer, digital sensor. Information is exchanged with the MCU through I2C communication.