[basic course of flight control development 1] crazy shell · open source formation UAV GPIO (LED flight information light and signal light control)

COCOFLY course
—— Crazy shell · UAV series
GPIO（LED Flight information light 、 Signal light control ）
    
    

    
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    One 、LED
    1.1LED brief introduction
    LED（Light Emitting Diode） It is the abbreviation of light emitting diode .LED It is a very common lighting device in life .LED There are many kinds of forms in our life , As shown in the figure below .
 

  
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    Even though LED There are many forms in our life , But all this LED In the circuit, the symbols shown in the figure below are used to represent .
    
    
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    1.2LED The principle of luminescence
    LED The most important light-emitting structure is the lamp beads as big as mung beans . Although its volume is very small , But it has heaven and earth inside , As shown in the figure below LED Internal construction .
    
    
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    This structure is extremely complex , It is divided into several layers ： The top layer is called P Type semiconductor layer 、 The middle layer is a light-emitting layer 、 The lowest layer is called N Type semiconductor layer .
    Understand from the perspective of Physics ： When the current passes through the chip ,N The electrons in a semiconductor are related to P The holes in A-type semiconductor collide and recombine violently in the light-emitting layer to produce photons , Emit energy in the form of photons （ The light you see ）.
    Two 、GPIO
    2.1GPIO brief introduction
    GPIO(General-purpose input/output), Short for general input and output , The pins of the single chip microcomputer can be used freely by users , Can be configured to output , It can also be configured as input . The output can be output “ High level ” perhaps “ Low level ”. In electronic circuits “ High level ” The voltage is high , Represented by logic is 1,“ Low level ” The voltage is low , Represented by logic is 0.
    STM32F103 Series is based on ARM Cortex M3 Kernel 32 Bit MCU , The main core used in flight control is 48 Foot's STM32F103CBT6, Its pins are shown in the figure below .
    
    
    
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    STM32F103CBT6 Of GPIO More functions , Yes A、B、C、D Wait for four groups GPIO, Each group GPIO All ports can be used as output ports except , It can also be used as a multiplexing pin , For example, serial port 、I2C、SPI And other special interface pins . However, it should be noted that the multiplexing function of each pin is limited , Therefore, it is necessary to pay attention to the multiplexing function of each pin when connecting the hardware , This can be STM32F103 In the data book of .GPIO There are altogether 8 Patterns , Respectively ： Floating input , Pull up input , Drop down input , Analog input , Open drain output , Push pull output , Push pull multiplexing , Open drain multiplexing function , As shown in the following table .
    STM32F103GPIO Working mode
    
    
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    this 8 We won't introduce the functions one by one , If you are interested, you can search the Internet to find out , Here we mainly explain the difference between open drain output and push-pull output .
    （1） Open drain output ：
    The output is equivalent to the collector of triode . You need to pull up the resistor to get a high level , Use the driving ability of external pull-up resistor , Reduce IC Internal drive , Strong driving power , It is suitable for current drive , Accessible 20mA.
    （2） Push pull output ：
    Can output high , Low level , Connect digital devices , It consists of two triodes with the same parameters or MOSFET Connect in push-pull mode , They are responsible for the amplification of positive and negative half cycle waveforms . When the circuit is working , Only one of the two symmetrical power switches is on at a time , So the conduction loss is small 、 Efficient , Both improve the load capacity of the circuit , And increase the switching speed .
    To sum up ： The push-pull output can output strong high and low levels , Connect digital devices ; The open drain output can only output low level , The high level depends on the external resistance . The output is equivalent to the collector of triode , To get a high level state, you need to pull up the resistor , It is suitable for current drive , Its ability to absorb current is relatively strong （ commonly 20ma within ）.
    2.2GPIO Related registers
    STM32F103 Each GPIO Ports have ： Two 32 Bit configuration register (GPIOx_CRL and GPIOx_CRH)、 Two 32 Bit data register (GPIOx_IDR and GPIOx_ODR)、 One 32 Position position / Reset register (GPIOx_BSRR)、 One 16 Bit reset register (GPIOx_BRR)、 One 32 Bit lock register (GPIOx_LCKR).
    （1）GPIOx_CRL register （x=A~G）
    
    
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    This register is used for configuration IO0~7 Input / output mode and rate setting .
    （2）GPIOx_CRH register （x=A~G）
    
    
    
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    This register is used for configuration IO8~15 Input / output mode and rate setting .
    （3）GPIOx_IDR register (x=A~G)
    
    
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    IDR yes GPIO Input data register . adopt IDR Registers can be read IO The state of . It should be noted that IDR Registers can only be written in words （16 position ） Read out in the form of .
    （4）GPIOx_ODR register (x=A~G)
    
    
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    ODR yes GPIO The output data register of . adopt ODR Registers can output high and low levels .
    （5）GPIOx_BSRR register (x=A~G)
    
    
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    BSRR yes GPIO Port bit setting of / Clear register .BSRR The height of the register 16 Bit is clear IO position , low 16 Bit is set IO position . It should be noted that BSRR Only writing 1 When , Only the corresponding function works , write in 0 It's invalid .
    （6）GPIOx_BRR register (x=A~G)
    
    
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    BRR yes GPIO Port bit clear register .BRR The foundation is only written 1 When , Only the corresponding function works , write in 0 Invalid .
    （7）GPIOx_LCKR register (x=A~G)
    
    
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    LCKR yes GPIO Port configuration lock register for .LCKR Registers are used to lock IO Port configuration , After setting , It cannot be configured except after reset IO The state of .
    
    2.3GPIO experiment
    The content of this experiment is to periodically light the flight information lights and signal lights of the UAV , Among them, the flight information light is under the four propellers , And the signal lights are on both sides of the switch .
    Looking at the schematic diagram, we can know that the flight information lights of the UAV are connected to NPN triode Q1 On , And the base of the triode is connected to the single chip microcomputer PA8 On ; Two signal lights are connected to PC13 and PC14 On .
    
    
    
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    The idea of writing code is shown in the following table
    
    
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    Follow the code idea , Write code （ By calling the official library ） As shown in the figure below ：
    
    
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    After completing the configuration, you only need to turn on and off periodically LED that will do .
    
    
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    The delay is shown in the figure below .
    
    
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    preservation 、 compile 、 download , As shown in the figure below ,1 For preservation ,2 To compile ,3 Download for .
    
    
    
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    Download the code to the flight control , You can see the flight control LED The indicator light and the navigation light under the four propellers flicker periodically , As shown in the figure below .
    
    
    
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