Line sensors: following a line for the first time

The sensor needs a clear picture: a light background and a dark line. For intermediate level tasks on the path you will also need an intersection.

1. Take a light matte field with a black line or stick black matte electrical tape on a white sheet: straight, smooth bend and one intersection.
2. Prepare two cards: white and black.
3. Find the left and right sensors on the robot. Put the robot on the line and check: does the line pass between the sensors and not touch any of them?

Prepare a track for your level and check if it suits your robot.

1. Make a path: straight, smooth bend, sharp arc and intersection. Prepare white and black cards.
2. Using a ruler, measure the width of the line and the distance between the sensors (between the centers of the windows).
3. Put the robot on the line. How many millimeters are left from the edge of the line to each sensor? Write in your journal: what happens if the line is wider than the distance between the sensors?

The sensor shines on the floor and measures how much light has returned. The board turns this into a number, and to see it, the program sends the number to the computer.

1. Create a sketch L31_Read_Sensors according to the template and write both parts yourself. The left sensor is connected to A4, right - to A5.

// Шаблон среднего уровня. Напиши код в разделе «Твоя часть» по целям в комментариях. const int LEFT_SENSOR_PIN = A4;const int RIGHT_SENSOR_PIN = A5; // ===== Твоя часть: напиши сам ===== void setup() {  // Включи связь с компьютером на той же скорости, что в мониторе порта: 9600.} void loop() {  // Пять раз в секунду печатай одну строку: L=число левого датчика  R=число правого.}

2. Upload the program and open the Serial Monitor with speed 9600.
3. Place a white card under the left sensor, then a black one. Keep the card at the same height as the sensor above the floor.

The sensor shines on the floor and measures how much light has returned. The left sensor is connected to A4, right - to A5.

Requirement. Sketch L31_Read_Sensors prints the line five times per second t=… L=… R=…, where t — time in milliseconds since switching on.

Acceptance.

1. By numbers t in the monitor, check that the lines are coming approximately every 200 ms. How many milliseconds does the interval differ from 200 and why?
2. Place a white card under the left sensor, then a black card at working height. Write down how much the number changes.

1. Fill out the table for the four robot positions:

2. Why are both numbers “white” in the last line, although the robot is on the line? Write it down.

Take it off profile sensors: how the numbers change while the line passes crosswise under the robot.

1. Place the robot across the line so that the line is far to the right of the right sensor.
2. Move the robot to the left in 5 mm steps until the line goes beyond the left sensor. Write down L and R at each step.

3. Draw two graphs in your journal: L and R versus shift. Find on the graph where the line is exactly between the sensors and how many millimeters you can go to the side until the sensor notices it.

The sensors are not the same: even over the same field their numbers are different. Therefore, each sensor needs its own measurements - calibration.

1. For each sensor, record three readings on white and three on black, in different places on the track.
2. Choose a typical number for each cell and write down why.

Calibrate the sensors and prove that the calibration can be trusted.

1. For each sensor, record 10 readings on white and 10 on black. Find the smallest and largest in each series - this is spread.
2. Compare the spread with the difference between white and black. How many times is the difference greater than the spread?
3. Repeat white near the window and in the dark corner of the classroom. Do the numbers change more than the spread?
4. Write down the conclusion: where the calibration can be trusted and when it needs to be repeated.

The program needs a rule: when to assume that there is a line under the sensor? Compare the new reading with two measurements: if it is closer to black than to white, there is a line under the sensor.

1. Create a sketch L31_Line_Detect according to the template and enter your four numbers instead of zeros.
2. Write loop() myself: deciding "line or not" for each sensor and printing.

// Шаблон среднего уровня. Напиши код в разделе «Твоя часть» по целям в комментариях. const int LEFT_SENSOR_PIN = A4;const int RIGHT_SENSOR_PIN = A5; // Впиши свои измерения из бортового журнала.const int LEFT_WHITE = 0;const int LEFT_BLACK = 0;const int RIGHT_WHITE = 0;const int RIGHT_BLACK = 0; // ===== Твоя часть: напиши сам ===== void loop() {  int leftValue = analogRead(LEFT_SENSOR_PIN);  int rightValue = analogRead(RIGHT_SENSOR_PIN);   // Для каждого датчика реши, линия ли под ним (правило «ближе к чёрному»): leftOnLine и rightOnLine.  // Печатай строку L=… R=…, а если под датчиком линия — допиши «слева линия» или «справа линия».  // Пять строк в секунду.} // ===== Готовое из прошлого шага — не меняй ===== void setup() {  Serial.begin(9600);}

3. Upload the program, open the Serial Monitor and place the black card under the sensors one by one.
4. Answer in the journal: what will the program start printing if white and black in it are mixed up? Why?

bool leftOnLine = abs(leftValue - LEFT_BLACK) < abs(leftValue - RIGHT_WHITE);

Requirement 1. Function onLine(value, white, black) replies true, when there is a line under the sensor:

• reading is closer to the black dimension than to the white dimension;
• works both when the sensor is black - a large number, and when it is small;
• there are no ready-made threshold numbers inside: only value, white and black.

Acceptance. Write onLine in the test sketch, load it and open the Serial Monitor (9600). The test checks eight cases for two types of sensors, including readings outside your measurements.

// Проверка функции onLine. Напиши функцию здесь, загрузи и открой монитор порта.// Когда все строки PASS, перенеси onLine в свою программу. // Требование 1: true, если показание ближе к чёрному, чем к белому.bool onLine(int value, int white, int black) {  return false;} int failed = 0; void expect(int value, int white, int black, bool expected) {  bool actual = onLine(value, white, black);  Serial.print(actual == expected ? "PASS " : "FAIL ");  Serial.print("onLine(");  Serial.print(value);  Serial.print(", ");  Serial.print(white);  Serial.print(", ");  Serial.print(black);  Serial.print(") = ");  Serial.print(actual ? "true" : "false");  Serial.print(", ожидаем ");  Serial.println(expected ? "true" : "false");  if (actual != expected) {    failed++;  }} void setup() {  Serial.begin(9600);   // Датчик, у которого чёрное — большое число, а белое — маленькое.  expect(780, 120, 780, true);  expect(120, 120, 780, false);  expect(600, 120, 780, true);  expect(300, 120, 780, false);  // За пределами измерений.  expect(900, 120, 780, true);  expect(50, 120, 780, false);  // Датчик, у которого наоборот: белое — большое число, чёрное — маленькое.  expect(300, 900, 120, true);  expect(700, 900, 120, false);   if (failed == 0) {    Serial.println("Все проверки пройдены");  } else {    Serial.print("Ошибок: ");    Serial.println(failed);  }} void loop() {}

When all lines PASS, add onLine into your program from the “See what the sensor sees” step and save it as L31_Line_Detect. Have her type “line on the left” and “line on the right.” Enter your measurements and check with the card.

The robot moves forward and the line must remain between the sensors. If the line was under one sensor, the robot moved to the side. The wheel can only move or stand still. How to return the robot to the line?

1. Place the switched off robot on the line. Move it so that the line is under the left sensor. Where did the robot go? Which way should he turn? Which wheel should I stop for this?
2. The same for the right sensor.
3. Fill out the table in the journal:

4. In your journal, explain in one sentence why stopping one wheel turns the robot.

The robot moves forward and the line must remain between the sensors. Make up the rules yourself: what the wheels do in each of the four cases and why.

1. Check each line with the robot turned off: move it with your hand and show where it should go.
2. "Both White" appears in two different robot positions. Which ones? Can the program distinguish between them? Write down what happens to the robot then.
3. On a straight track, “both are a line” almost never happens. Where on the final field will this occur and what should the robot do then?

Let's put everything together: sensors, the “closer to black” rule and motors from lesson 2.1. The wheels will obey the rules from your table.

1. Create a sketch L31_First_Line according to the template. Enter your four dimensions. Motor tuning and protection are already ready.
2. Write loop() himself: transfer your conditions from L31_Line_Detect, set the wheels to speed according to your table of rules and send them to the motors.

// Шаблон среднего уровня. Напиши код в разделе «Твоя часть» по целям в комментариях. const int LEFT_SENSOR_PIN = A4;const int RIGHT_SENSOR_PIN = A5; // Впиши свои измерения из бортового журнала.const int LEFT_WHITE = 0;const int LEFT_BLACK = 0;const int RIGHT_WHITE = 0;const int RIGHT_BLACK = 0;const int LEFT_DIR_PIN = 7;const int LEFT_SPEED_PIN = 6;const int RIGHT_DIR_PIN = 4;const int RIGHT_SPEED_PIN = 5;const int FORWARD = HIGH;int speed = 100; // начальная скорость, подбираем на подставке // ===== Твоя часть: напиши сам ===== void loop() {  int leftValue = analogRead(LEFT_SENSOR_PIN);  int rightValue = analogRead(RIGHT_SENSOR_PIN);   // Реши, линия ли под каждым датчиком, — перенеси свои условия из L31_Line_Detect.  // Колёса выполняют твою таблицу правил: линия под датчиком — его колесо стоит.  // Колесо, которое правило остановило, снова едет, когда его датчик видит белое.} // ===== Готовое: настройка и защита — не меняй ===== void setup() {  pinMode(LEFT_DIR_PIN, OUTPUT);  pinMode(LEFT_SPEED_PIN, OUTPUT);  pinMode(RIGHT_DIR_PIN, OUTPUT);  pinMode(RIGHT_SPEED_PIN, OUTPUT);   analogWrite(LEFT_SPEED_PIN, 0);  analogWrite(RIGHT_SPEED_PIN, 0);  digitalWrite(LEFT_DIR_PIN, FORWARD);  digitalWrite(RIGHT_DIR_PIN, FORWARD);   // Без измерений робот не поедет: программа остановится здесь.  if (LEFT_WHITE == LEFT_BLACK || RIGHT_WHITE == RIGHT_BLACK) {    while (true) {    }  }   delay(2000); // время убрать руки от робота}

3. Click Check.

Take the frame: it contains contacts, motors and function drive from lesson 2.1. Transfer your measurements and function into it onLine and save as L31_First_Line. You will need this program in lesson 3.2.

// Каркас движения по линии. Требования к программе — в тексте урока.const int LEFT_SENSOR_PIN = A4;const int RIGHT_SENSOR_PIN = A5; // Впиши свои измерения из бортового журнала.const int LEFT_WHITE = 0;const int LEFT_BLACK = 0;const int RIGHT_WHITE = 0;const int RIGHT_BLACK = 0; const int LEFT_DIR_PIN = 7;const int LEFT_SPEED_PIN = 6;const int RIGHT_DIR_PIN = 4;const int RIGHT_SPEED_PIN = 5;const int FORWARD = HIGH; void drive(int leftDir, int leftSpeed, int rightDir, int rightSpeed) {  digitalWrite(LEFT_DIR_PIN, leftDir);  digitalWrite(RIGHT_DIR_PIN, rightDir);  analogWrite(LEFT_SPEED_PIN, leftSpeed);  analogWrite(RIGHT_SPEED_PIN, rightSpeed);} // Требование 1: перенеси функцию onLine из тестового скетча.bool onLine(int value, int white, int black) {  return false;} void setup() {  pinMode(LEFT_DIR_PIN, OUTPUT);  pinMode(LEFT_SPEED_PIN, OUTPUT);  pinMode(RIGHT_DIR_PIN, OUTPUT);  pinMode(RIGHT_SPEED_PIN, OUTPUT);  drive(FORWARD, 0, FORWARD, 0);   // Требование 3: защита от запуска без измерений и время убрать руки.} void loop() {  // Требование 2: прочитать датчики, решить по своей таблице правил, задать скорости.  drive(FORWARD, 0, FORWARD, 0);}

Requirement 2. Wheels follow your rules table:

• in each repetition the program reads both sensors anew and decides anew: the wheel, stopped once, moves again when its sensor sees white;
• your function makes the decision onLine;
• speed - one named variable speed at the beginning of the sketch.

Requirement 3. The robot is safe:

• without measurements, white and black wheels stand;
• after turning on, you have 2 seconds to remove your hands.

Acceptance - on the stand in the next step: the robot performs every line of your rule table, and without measurements the wheels don’t spin.

1. Place the robot on the stand, load the program, turn on the power to the motors.
2. Check all four rows of your rules table: place the cards so that the sensors see what you need. Write down what the wheels do.

3. Check your prediction about the speed specified in setup(). Turn off the power to the motors.

Acceptance of requirements 2–3 on a stand.

1. Load the program with zeros instead of measurements. The wheels should not spin. Enter the measurements and upload again.
2. Check each line of your rules table with cards.
3. Note how many seconds after switching on the wheels start moving.

1. Turn off the power to the motors, unplug the USB cable.
2. Place the robot on a straight line: the line between the sensors. Turn on the power. Be prepared to turn it off if the robot leaves the path.
3. Walk the path three times at speed = 100, then three times at 80 and at 130. Record how many times the robot went through the bend.

4. Why does the robot move jerkily? Write it down in one sentence.

1. Turn off the power to the motors, disconnect the USB cable. Be prepared to turn off the power if the robot leaves the track.
2. Find the largest speed, in which the robot goes through a smooth bend three times out of three. Start at 80 and work your way up in 20 steps.
3. At the highest speed, which the robot could not withstand, look where it loses the line. Explain the reason in the journal through your rule table.
4. Write down what needs to be changed in the rules to make the robot keep the line faster. You will check this in lesson 3.2.