[flight control development foundation tutorial 4] crazy shell · open source formation UAV - serial port (optical flow data acquisition)

COCOFLY course
—— Crazy shell · Unmanned aerial vehicle (uav) · series
A serial port （ Optical flow data acquisition ）
    
    

    
    
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    One 、 Introduction to optical flow module
    Optical flow （optical flow） It refers to the instantaneous speed of the pixel motion of the space moving object on the observation imaging plane .
    Optical flow method uses the changes of pixels in the time domain and the correlation between adjacent frames in the image sequence to find the corresponding relationship between the previous frame and the current frame , A method to calculate the motion information of objects between adjacent frames .
    Usually, the instantaneous change rate of gray level on a specific coordinate point of two-dimensional image plane is defined as optical flow vector .
    generally speaking , Optical flow is due to the movement of the foreground target itself in the scene 、 The motion of the camera , Or the joint movement of the two .
    When a person's eyes observe a moving object , The scene of an object forms a series of continuously changing images on the retina of the human eye , This series of continuously changing information is constantly “ Flow through ” retina （ Image plane ）, Like a kind of light “ flow ”, So it is called optical flow . Optical flow expresses the change of image , Because it contains the information of target motion , Therefore, it can be used by the observer to determine the movement of the target .
    COCOFLY The optical flow module used by UAV is based on PMW3901,PMW3901 It is an optical motion tracking sensor , The sensor is small 、 Low power consumption 、 High precision . As shown in the figure below, the physical drawing of the optical flow module is shown in the figure below .
    
    
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    The optical flow module has PMW3901 Good data processing , And transmit periodically through serial port , The baud rate is 19200, The serial port transmission protocol of the optical flow module is shown in the table below .
    
    
    surface 1
    among DATA0、DATA1 yes flow_x Split low 8 Bit data and high 8 Bit data , namely flow_x=(int16_t)(DATA1<<8)|(DATA0),DATA2、DATA3 yes flow_y It's low 8 Position and height 8 position , namely flow_y=(int16_t)(DATA3<<8)|(DATA2), Where the sum check is DATA0~DATA3 The cumulative value of , namely SUM=DATA0+DATA1+DATA2+DATA3;SQUAL For the ground environmental quality , The larger the value, the higher the ground environmental quality ; The last byte is the terminator , There are two kinds of ： Fixed in normal mode is 0xAA(Y Pin to high level )、 It is fixed in yaw mode 0xBB（Y Pin connected to low level ）. Two 、 Serial optical flow data acquisition experiment
    Serial optical flow data acquisition experiment use STM32 Serial port 2 namely UART2 Connected with optical flow module , A serial port 1 namely UART1 adopt USB Connect the serial port module to the computer , Put the serial port 2 The obtained optical flow data passes through the serial port 1 The serial port debugging assistant transmitted to the computer is displayed . A serial port 2 The pins are shown in the figure below ：
    
    
    chart 3
    The two serial port pins are respectively connected with PA2 And PA3 Pin to pin , Then we are right PA2 And PA3 Pin configuration , A serial port 1 The configuration of can refer to 《 A serial port （ Basic transceiver ）》, Configuration code （ By calling the official library ） The idea of writing is as follows ：
    
    
    surface 2
    A serial port 2 The initialization code is as follows ：
    
    
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    A serial port 2 The data received from the optical flow module is forwarded to the serial port 1, A serial port 2 The interrupt function code of is as follows .
    
    
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    Set the serial port 2 The baud rate of is 19200, The code is as follows ：
    
    
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    preservation 、 compile 、 Download code , Ensure serial port 2 Connect the optical flow module , Then put the serial port 1 Connect
    USB Serial port module , Finally connected to the computer USB port , As shown in the figure below ：
    
    
    chart 7
    Then I'm putting USB Plug the serial transfer module into the computer USB mouth , Open the serial port debugging assistant on the computer , Find the corresponding COM mouth （ The premise is that USB Serial port drive ）, Set the baud rate to 115200, open , You can see that the serial port is constantly printing the data sent by the optical flow module , As shown in the figure below .
    
    
    chart 8