Project Roadmap
Part 1 - Experimental Smart Assistive Platform for Elderly and Disabled People
Part 3 - Wireless Command and H-Bridge Direct Drive
Part 4 - Introducing Autonomous Line Following (TCRT5000)
Part 5 - Non-Contact Proactive Shielding (HC-SR04 Range Finder)
Part 6 - Strict Priority Hierarchy with Tactile Mechanical Bumpers
Part 7 - Mobile Robot Control and Live Video Streaming
An autonomous tracking system can easily collide with static roadblocks. To mitigate this risk, we add an Ultrasonic Distance Module (HC-SR04). This sensor proactively measures the distance to upcoming obstacles by calculating the time-of-flight of high-frequency audio pings.To prevent software lag, we supply a 30,000 microsecond hardware limit to the pulseIn() function. This prevents the script from freezing if the sensor misses an echo pulse. If the calculated clearance falls beneath 30 cm, the robot suspends line tracking and maneuvers away.
Here, the vehicle gains a contact-free defensive boundary. While navigating autonomously, if the ultrasonic sonar module captures a barrier closing within 30 cm, the robot overrides line following to execute a sharp evasive turn away from danger.
The sensor module is mounted on the contact board:
The complete vehicle intended for testing looks as follows:
Essential Code Snippets Related to the Ultrasonic Sensor
1. Hardware Pin Definitions
Pin assignments for the HC-SR04 sonar module:
// Ultrasonic HC-SR04 Sonar Pins
const int TRIG_PIN = 4;
const int ECHO_PIN = 3;
2. Pin Setup in setup()
Configures TRIG_PIN to output pulses and ECHO_PIN to listen for returning sound waves:
// Ultrasonic Sonar pins configuration
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
3. Distance Measurement Routine (getDistance())
Generates a 10us ultrasonic burst and measures echo response time to calculate distance in centimeters. Includes a 30 ms hardware timeout to prevent code execution freezes:
float getDistance() {
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(2);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
// 30ms hardware timeout constraint to avoid freezing the main execution loop
long duration = pulseIn(ECHO_PIN, HIGH, 30000);
float d = duration * 0.0343 / 2;
if (d == 0) return 999.0; // Return out-of-bounds constant on reading error
return d;
}
4. Obstacle Avoidance Logic in loop()
When operating in MODE_AUTONOMOUS, distance is checked before line tracking logic. If an obstacle is detected closer than 30 cm, line tracking is temporarily overridden, and the robot performs an evasive left turn:
else if (currentMode == MODE_AUTONOMOUS) {
float distance = getDistance();
// Obstacle avoidance matching Elecrow's motor logic and 0.3s timing
if (distance < 30.0) {
Serial.println("Obstacle detected! Turning left...");
driveMotors(MOTOR_SPEED, 0, 0, MOTOR_SPEED); // Spin Left in place
delay(300); // Turn duration
}
else {
// Standard Line Tracking routine executes here...
}
}
Full Code
The full code for this stage is as follows:
#include <Arduino.h>
#include <Arduino_LED_Matrix.h> // Library for the 8x13 LED matrix
Arduino_LED_Matrix matrix; // Initialize LED matrix object
// L9110S Motor Driver Pins
const int MOTOR_PIN_A1 = 5;
const int MOTOR_PIN_A2 = 6;
const int MOTOR_PIN_B1 = 9;
const int MOTOR_PIN_B2 = 10;
// Infrared Receiver Pin
const int IR_RECEIVE_PIN = 2;
// Line Tracking Sensor Pins
const int TRACKING_PIN_L = A2;
const int TRACKING_PIN_R = A3;
// Ultrasonic HC-SR04 Sonar Pins
const int TRIG_PIN = 4;
const int ECHO_PIN = 3;
enum RobotMode {
MODE_MANUAL,
MODE_AUTONOMOUS
};
RobotMode currentMode = MODE_MANUAL;
// Speed settings
const int MOTOR_SPEED = 200;
const int TRACK_SPEED = 160;
byte lastCommand = 0;
// LED Matrix Frame Buffer Size (104 pixels)
const uint8_t FRAME_SIZE = 8 * 13;
// --- LED MATRIX ARROW & ICON ARRAYS (Brightness levels 0-7) ---
uint8_t arrow_up[FRAME_SIZE] = {
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 7, 7, 7, 0, 0, 0, 0, 0,
0, 0, 0, 0, 7, 7, 7, 7, 7, 0, 0, 0, 0,
0, 0, 0, 7, 7, 0, 7, 0, 7, 7, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0
};
uint8_t arrow_down[FRAME_SIZE] = {
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0,
0, 0, 0, 7, 7, 0, 7, 0, 7, 7, 0, 0, 0,
0, 0, 0, 0, 7, 7, 7, 7, 7, 0, 0, 0, 0,
0, 0, 0, 0, 0, 7, 7, 7, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0
};
uint8_t arrow_left[FRAME_SIZE] = {
0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 7, 7, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
0, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
0, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
0, 0, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
0, 0, 0, 7, 7, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0
};
uint8_t arrow_right[FRAME_SIZE] = {
0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 7, 7, 0, 0, 0,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 0, 0,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 0,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 0,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 7, 7, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0
};
uint8_t stop_icon[FRAME_SIZE] = { 0 };
// --- ONBOARD RGB LED FUNCTIONS ---
void set_led3_color(int r, int g, int b) {
analogWrite(LED3_R, r);
analogWrite(LED3_G, g);
analogWrite(LED3_B, b);
}
void set_led4_color(bool r, bool g, bool b) {
digitalWrite(LED4_R, r ? LOW : HIGH);
digitalWrite(LED4_G, g ? LOW : HIGH);
digitalWrite(LED4_B, b ? LOW : HIGH);
}
// Elecrow IR Decoder
long readElecrowIR() {
int count = 0;
while (digitalRead(IR_RECEIVE_PIN) == LOW && count < 200) { count++; delayMicroseconds(60); }
if (count >= 200) return -1;
count = 0;
while (digitalRead(IR_RECEIVE_PIN) == HIGH && count < 80) { count++; delayMicroseconds(60); }
if (count >= 80) return -1;
int idx = 0, cnt = 0;
byte data[4] = {0, 0, 0, 0};
for (int i = 0; i < 32; i++) {
count = 0;
while (digitalRead(IR_RECEIVE_PIN) == LOW && count < 15) { count++; delayMicroseconds(60); }
count = 0;
while (digitalRead(IR_RECEIVE_PIN) == HIGH && count < 40) { count++; delayMicroseconds(60); }
if (count > 8) data[idx] |= (1 << cnt);
if (cnt == 7) { cnt = 0; idx++; } else { cnt++; }
}
if ((byte)(data[0] + data[1]) == 0xFF && (byte)(data[2] + data[3]) == 0xFF) {
return data[2];
}
return -1;
}
void driveMotors(int a1, int a2, int b1, int b2) {
analogWrite(MOTOR_PIN_A1, a1);
analogWrite(MOTOR_PIN_A2, a2);
analogWrite(MOTOR_PIN_B1, b1);
analogWrite(MOTOR_PIN_B2, b2);
}
float getDistance() {
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(2);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
long duration = pulseIn(ECHO_PIN, HIGH, 30000);
float d = duration * 0.0343 / 2;
if (d == 0) return 999.0;
return d;
}
void executeCommand(byte command) {
switch (command) {
case 0x1C: // OK Button - Toggle Manual / Autonomous Operations
if (currentMode == MODE_MANUAL) {
currentMode = MODE_AUTONOMOUS;
Serial.println("Mode changed: AUTONOMOUS (Tracking + Sonar)");
}
else {
currentMode = MODE_MANUAL;
driveMotors(0, 0, 0, 0);
set_led4_color(false, false, false);
set_led3_color(0, 0, 0);
matrix.draw(stop_icon);
Serial.println("Mode changed: MANUAL (IR Control)");
}
lastCommand = 0;
delay(500);
break;
case 0x18: // Forward
if (currentMode == MODE_MANUAL) {
driveMotors(0, MOTOR_SPEED, 0, MOTOR_SPEED);
set_led4_color(false, true, false); // Green
set_led3_color(0, 200, 0);
matrix.draw(arrow_up);
}
break;
case 0x08: // Spin Left
if (currentMode == MODE_MANUAL) {
driveMotors(MOTOR_SPEED, 0, 0, MOTOR_SPEED);
set_led4_color(false, false, true); // Blue
set_led3_color(0, 0, 200);
matrix.draw(arrow_left);
}
break;
case 0x5A: // Spin Right
if (currentMode == MODE_MANUAL) {
driveMotors(0, MOTOR_SPEED, MOTOR_SPEED, 0);
set_led4_color(false, false, true); // Blue
set_led3_color(0, 0, 200);
matrix.draw(arrow_right);
}
break;
case 0x52: // Backward
if (currentMode == MODE_MANUAL) {
driveMotors(MOTOR_SPEED, 0, MOTOR_SPEED, 0);
set_led4_color(true, false, false); // Red
set_led3_color(200, 0, 0);
matrix.draw(arrow_down);
}
break;
default:
if (currentMode == MODE_MANUAL) {
driveMotors(0, 0, 0, 0);
set_led4_color(false, false, false);
set_led3_color(0, 0, 0);
matrix.draw(stop_icon);
}
break;
}
}
void setup() {
Serial.begin(115200);
pinMode(IR_RECEIVE_PIN, INPUT_PULLUP);
pinMode(TRACKING_PIN_L, INPUT_PULLUP);
pinMode(TRACKING_PIN_R, INPUT_PULLUP);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
// RGB LED Pin Configuration
pinMode(LED4_R, OUTPUT);
pinMode(LED4_G, OUTPUT);
pinMode(LED4_B, OUTPUT);
set_led3_color(0, 0, 0);
set_led4_color(false, false, false);
// Initialize LED Matrix
matrix.begin();
matrix.setGrayscaleBits(3); // 8 brightness levels (0-7)
matrix.clear();
Serial.println("System Ready on Arduino UNO Q (IR + Line Tracking + Sonar + Matrix/LEDs).");
}
void loop() {
// 1. Process incoming IR signals
if (digitalRead(IR_RECEIVE_PIN) == LOW) {
long result = readElecrowIR();
if (result != -1) {
lastCommand = (byte)result;
executeCommand(lastCommand);
}
}
// 2. Continuous Mode Execution
if (currentMode == MODE_MANUAL) {
if (digitalRead(IR_RECEIVE_PIN) == HIGH) {
driveMotors(0, 0, 0, 0);
set_led4_color(false, false, false);
set_led3_color(0, 0, 0);
matrix.draw(stop_icon);
} else {
executeCommand(lastCommand);
}
}
else if (currentMode == MODE_AUTONOMOUS) {
float distance = getDistance();
// Priority 1: Ultrasonic Obstacle Avoidance
if (distance < 30.0) {
Serial.println("Obstacle detected! Evading left...");
driveMotors(MOTOR_SPEED, 0, 0, MOTOR_SPEED); // Spin Left in place
set_led4_color(true, false, false); // Red warning
set_led3_color(200, 0, 0);
matrix.draw(arrow_left); // Indicate left evasion turn
delay(300); // Turn duration
}
// Priority 2: Line Tracking Routine
else {
int trackL = digitalRead(TRACKING_PIN_L);
int trackR = digitalRead(TRACKING_PIN_R);
int trackState = (trackL * 2) + trackR;
switch (trackState) {
case 0: // Off track -> Stop
driveMotors(0, 0, 0, 0);
set_led4_color(false, false, false);
set_led3_color(0, 0, 0);
matrix.draw(stop_icon);
break;
case 1: // Right sensor active -> Turn Right
driveMotors(0, TRACK_SPEED, TRACK_SPEED, 0);
set_led4_color(false, false, true); // Blue
set_led3_color(0, 0, 200);
matrix.draw(arrow_right);
break;
case 2: // Left sensor active -> Turn Left
driveMotors(TRACK_SPEED, 0, 0, TRACK_SPEED);
set_led4_color(false, false, true); // Blue
set_led3_color(0, 0, 200);
matrix.draw(arrow_left);
break;
case 3: // Both sensors active -> Move Forward
driveMotors(0, TRACK_SPEED, 0, TRACK_SPEED);
set_led4_color(false, true, false); // Green
set_led3_color(0, 200, 0);
matrix.draw(arrow_up);
break;
}
delay(10);
}
}
}