2019/05/25

Light Tracking Gimbal



Preface

Based on my previous project (Joystick Control Gimbal), I slightly modified it into a Light Tracking device.  It took me about two days to fine-tune the Light Tracking Gimbal to move smoothly and hold its position while light source is not moving.

Goal of this tutorial

Let's see the video below to see what's the final result of this tutorial.


Gimbal Panel Area

There are Top Left, Top Right, Bottom Left, and Bottom Right.
In each area, there is a light sensor.



Programming Logic:

  1. Get reading from 4 photo sensors 
    • I sample each sensor 10 times and then get the average value to ensure the readings are more stable
  2. Get average of each side
    • Top side value = (Top left + Top right) / 2
    • Bottom side value = (Bottom left + Bottom right) / 2
    • Left side value = (Top left + Bottom left ) / 2
    • Right side value = (Top right + Bottom right ) / 2
  3. Compare all four sides to see which side has bigger value
  4. Move the servo towards the biggest side among four side
  5. Tolerance variable is in control whether to move or not based on how much differences among four sides. If reading values from four sides were within the range of 100, then keep the Gimbal static(Hold it's position) (default value = 100)
Tolerance variable is the most important variable to ensure the Gimbal holds its position when four light sensors get values within the defined tolerance!

Component Needed for this project

  • Arduino Nano * 1
  • SG90 Servo * 2
  • Light sensors * 4
  • 10K Resistors * 4
  • Prontoboard * 1
  • Many jump wires
  • Extra long wires for photo sensor connect * 4
  • Heat shrink tube 2cm * 4

Tools Needed

  • Soldering gun * 1
  • Diagonal cutting pliers * 1
  • Screw driver * 1
  • Few screws * 10
  • Double sided tape

Schematic: (I use fritzing for this schematic)



Program Code:

*************************************************************
*** Please click subscribe my YouTube Channel before use the code 
*** There is no restriction, but I would be really appreciated 
*** if you did. Thank you!  **************************************************************

*************************************************************
*** 在 Copy 底下程式碼之前,請按下底下按鈕,訂閱我的 YouTube 頻道! 
*** 雖沒有強制規定,不過如果你有訂閱的話,非常感謝你! 
**************************************************************
/**
   Author: Kevin Chen AKA Stonez56 
   My Blog to see more tutorials: https://stonez56.blogspot.com
   Date: 2019/05/11 The day before mother's day

    Program function flow
   1. Reading four light sensor values
   2. Average top two(Top left, Top right), bottom two(Bottom left, Bottom right)
   3. Average left two(Top left, Bottom left), right two (Top right, Bottom right)
   4. Compare 4 averaged value and make servo mave toward the biggest number side
   
   v0 Light traking Gimbal base to get readings
   v1 Write servo code in and move servo accordingly

                    |
         Top left   |     Top right
   -----------------+----------------------
     Bottom left   |  Bottom right
                    |
*/
#include <Servo.h>
Servo servo1_x;
Servo servo2_y;

//Light Sensor Pin definitions
const uint8_t  light_top_left_PIN = A6;
const uint8_t  light_bottom_left_PIN = A5;
const uint8_t  light_top_rigth_PIN = A2;
const uint8_t  light_bottom_right_PIN = A1;
//Potentiometer pin
const  int potPIN = A0;
//Servo pins
const int servo1_x_pin = 2;
const int servo2_y_pin = 4;


//User define variables
// Gimbal movement tolerance 50~255
byte gimbal_movement_tolerance = 100;
//Photo sensor max reading times for average (for more accuracy)
byte max_reading = 10;
// define original servo angle
uint8_t originalAngle = 92;
uint8_t x_last = originalAngle;  // X last postion
uint8_t y_last = originalAngle; // Y last postion
uint8_t moveSpeed = 10;  //How fast show this Servo move
uint8_t maxSpeed = 50; //Max speed
uint8_t minSpeed = 1;
uint8_t y_minAngle = 1;  //Mimum angle
uint8_t y_maxAngle = 180;  //Maximum angle
uint8_t x_minAngle = 90;  //Mimum angle
uint8_t x_maxAngle = 180;  //Maximum angle

void setup() {
  Serial.begin(57600);

  pinMode(light_top_left_PIN, INPUT);
  pinMode(light_bottom_left_PIN, INPUT);
  pinMode(light_top_rigth_PIN, INPUT);
  pinMode(light_bottom_right_PIN, INPUT);

  servo1_x.attach(servo1_x_pin);
  servo1_x.write(originalAngle); //move servo to defined angle
  servo2_y.attach(servo2_y_pin);
  servo2_y.write(originalAngle); //move servo to defined angle

  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, LOW);

}

void loop() {
  char moveTowards = ' ';


  int potValue = analogRead(potPIN);
  Serial.print(F("potValue: "));
  Serial.println(potValue);
  moveSpeed = map(potValue, 0, 500, minSpeed, maxSpeed);
  Serial.print(F("moveSpeed: "));
  Serial.println(moveSpeed);
  moveTowards = getFacingToward(); //find out which side to move


//  Serial.print(F("moveTowards: "));
//  Serial.println(moveTowards);
  moveServo(moveTowards);

  delay(80);
}

void moveServo(char moveTowards) {


  //previous position were stored in x_last, y_last
  switch (moveTowards) {
    case 'T': //Move towards top
      if (x_last - moveSpeed < x_minAngle) {
        x_last = x_minAngle;
        servo1_x.write(x_last);
      } else {
        x_last -= moveSpeed;
        servo1_x.write(x_last);
      }
      break;
    case 'B': //Move towards bottom
      if (x_last + moveSpeed > x_maxAngle) {
        x_last = x_maxAngle;
        servo1_x.write(x_last);
      } else {
        x_last += moveSpeed;
        servo1_x.write(x_last);
      }
      break;
    case 'L': //Move towards left
      if (y_last - moveSpeed < y_minAngle) {
        y_last = y_minAngle;
        servo2_y.write(y_last);
      } else {
        y_last -= moveSpeed;
        servo2_y.write(y_last);
      }
      break;
    case 'R':
      if (y_last + moveSpeed > y_maxAngle) {
        y_last = y_maxAngle;
        servo2_y.write(y_last);
      } else {
        y_last += moveSpeed;
        servo2_y.write(y_last);
      }
      break;
    default:
      //Don't move servo
      break;
  }

}

/**
   This fuction get reading max_reading times and return average
   if it sees an 0, it will skip it
*/
int averageReading(int PIN, byte max_reading) {
  int total = 0;
  int current = 0;

  for (byte i = 0; i <= max_reading; i++) {
    current = analogRead(PIN);
    if (current == 0) {
      current = analogRead(PIN);
    }
    total += current;
  }

  return total / (max_reading);
}

/**


   Parameters: N/A
   Return: char; T, B, R, L to indicate the moving directoin
                       '-' means not moving at all
*/
char getFacingToward() {
  //1. Read each pin max_reading times

  int top_left = averageReading(light_top_left_PIN, max_reading);
  int bottom_left = averageReading(light_bottom_left_PIN, max_reading);
  int top_right = averageReading(light_top_rigth_PIN, max_reading);
  int bottom_right = averageReading(light_bottom_right_PIN, max_reading * 3);

  //Show photo sensor readings...
  Serial.print(F("Top left-A6: "));
  Serial.println(top_left);
  Serial.print(F("Bottom left-A5: "));
  Serial.println(bottom_left);
  Serial.print(F("Top right-A2: "));
  Serial.println(top_right);
  Serial.print(F("Bottom rightA1: "));
  Serial.println(bottom_right);

  //2. Get max value sides(two averaged, see above)
  byte go_direction[4] = {0, 0, 0, 0};
  int toward[4] = {0, 0, 0, 0}; //Top, Bottom, Left, Right
  toward[0] = (top_left + top_right) / 2 ;
  toward[1] = (bottom_left + bottom_right) / 2 ;
  toward[2] = (top_left + bottom_left) / 2;
  toward[3] = (top_right + bottom_right) / 2;

  //3. Add all side and average,
  //    if each side is within the tolerance then don't move Gimbal
  //    average = toward[0] +...toward[3]
  //    average - toward[0] .... toward[3], if all within gimbal_movement_tolerance, then no move
  int total_toward = 0;
  total_toward += toward[0];
  total_toward += toward[1];
  total_toward += toward[2];
  total_toward += toward[3];
  //get average
  int total_average = total_toward / 4; //4 sides
  Serial.print(F("total_average:"));
  Serial.println(total_average);
  //    if each side is within the tolerance then don't move Gimbal
  boolean shouldMove = false;
  //else move the gimbal
  if (total_average - toward[0] > gimbal_movement_tolerance) shouldMove = true;
  if (total_average - toward[1] > gimbal_movement_tolerance) shouldMove = true;
  if (total_average - toward[2] > gimbal_movement_tolerance) shouldMove = true;
  if (total_average - toward[3] > gimbal_movement_tolerance) shouldMove = true;

  Serial.print(F("toward 0 TOP : "));
  Serial.println(toward[0]);
  Serial.print(F("toward 1 BOTTOM: "));
  Serial.println(toward[1]);
  Serial.print(F("toward 2 LEFT: "));
  Serial.println(toward[2]);
  Serial.print(F("toward 3 RIGHT: "));
  Serial.println(toward[3]);

  //Find the biggest number to decide which side to go,
  // but if four values are quite similar, send '-' back to indicate not moving
  char facing = ' ' ;
  if (shouldMove) {
    int max_ = 0;
    if (toward[0] > max_) {
      max_ = toward[0];
      facing = 'T';
    }
    if (toward[1] > max_) {
      max_ = toward[1];
      facing = 'B';
    }
    if (toward[2] > max_) {
      max_ = toward[2];
      facing = 'L';
    }
    if (toward[3] > max_) {
      max_ = toward[3];
      facing = 'R';
    }
  } else {
    facing = '-'; //no need to move
  }
  //  Serial.print(F("shouldMove: "));
  //  Serial.println(shouldMove);
  return facing;
}



References:

  1. Serveo Example: https://www.instructables.com/id/4-Simple-Servo-Project-with-Arduino/ 
  2. Light Sensor Example: https://maker.pro/arduino/tutorial/how-to-use-an-ldr-sensor-with-arduino 
  3. 3D Gimbal base model: https://www.thingiverse.com/thing:2892903
    You probably need slight modification to this model to be able to fix the base... I did
====================THE END============

中文版


前言

根據我之前做的專案(Arduino 用搖桿控制的雙向轉軸的平台),我稍微將它修改為一個光源追蹤裝置。 主要的時間是花在微調在雲台伺服器的控制上,以便它光源不動的情況下,平穩移動並保持其位置。

專案目標

讓我們看一下下面的成果影片,看看本次教學的最終成果:


雲台分區

分為左上角,右上角,左下角,右下角,每一個分區內,各有一顆光敏電阻。


程式邏輯

  1. 從4個光敏電阻讀取訊號數值:
    • 為了得到了更穩定的數值,每個光敏電阻採樣10次,然後取得到平均值。
  2. 取得到每一方向的平均值
    • 上方值=(左上角+右上角)/ 2
    • 下方值=(左下角+右下角)/ 2
    • 左邊值=(左上角+左下角)/ 2
    • 右邊值=(右上角+右下角)/ 2
  3. 比較所有四個方向面,找出更大的值的方向
  4. 將伺服機雲台朝向向大的值方向移動
  5. Tolerance variable 根據四邊之間的差異來控制是否移動。如果四個方向的值大小在 100以內,則伺服機雲台保持不動。(默認值= 100)

所需零件

  • Arduino Nano * 1
  • SG90 伺服馬達 * 2
  • 光敏電阻 * 4
  • 10K 電阻* 4
  • 洞洞板 * 1
  • 許多單蕊線
  • 稍長一些的單蕊線(接光敏電阻用) * 4
  • 熱縮套管 2cm * 4

所需工具

  • 焊鎗工具 * 1
  • 斜口鉗 * 1
  • 縲絲刀 * 1
  • 小縲絲 * 10
  • 雙面膠

線路圖: (我是用 fritzing 工具製作)



程式碼:

請參考英文版上方。

參考資料:

  1. 伺服器: https://www.instructables.com/id/4-Simple-Servo-Project-with-Arduino/ 
  2. 光敏電阻: https://maker.pro/arduino/tutorial/how-to-use-an-ldr-sensor-with-arduino 
  3. 3D 雲台模型: https://www.thingiverse.com/thing:2892903
    個雲台的底座螺絲孔過大,導致 SG90 所附螺絲無法直接鎖緊。要請高手出來修改一下! 

全文完

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