Obstacle Avoidance Master

Overview

Obstacle avoidance is an important intelligent function of drones. In this project, you will learn how to use ultrasonic sensors to implement front obstacle avoidance.

What You’ll Learn

• Ultrasonic sensor principles
• Sensor interface programming
• Conditional logic design
• Real-time control

Materials Needed

Item	Quantity	Notes
ESP32 Drone	1	-
HC-SR04 Ultrasonic Module	1	Distance measurement sensor
Breadboard, Dupont Lines	Several	For connections

Step 1: Hardware Wiring

Connect HC-SR04 to ESP32:

HC-SR04	ESP32
VCC	5V
GND	GND
Trig	GPIO 18
Echo	GPIO 19

Step 2: Open the Project

Extract obstacle_avoid.zip and open with VS Code.

Step 3: Write Distance Measurement Function

Open ultrasonic.c and implement ultrasonic_get_distance function:

float ultrasonic_get_distance(void) {
  // 1. Send 10us trigger signal
  gpio_set_level(TRIG_PIN, 1);
  ets_delay_us(10);
  gpio_set_level(TRIG_PIN, 0);

  // 2. Measure Echo high level duration
  uint32_t start = 0, end = 0;
  while (!gpio_get_level(ECHO_PIN)) start = esp_timer_get_time();
  while (gpio_get_level(ECHO_PIN)) end = esp_timer_get_time();

  // 3. Calculate distance: sound speed 340m/s, distance = time * speed / 2
  float distance = (end - start) * 0.034 / 2;
  return distance;
}

Step 4: Add Obstacle Avoidance Logic

Open flight_control.c and add to the main loop:

float distance = ultrasonic_get_distance();
if (distance < 50) { // Distance less than 50cm
  if (distance < 20) { // Distance less than 20cm
    // Emergency brake
    motorsSetRatio(MOTOR_M1, 0);
    motorsSetRatio(MOTOR_M2, 0);
    motorsSetRatio(MOTOR_M3, 0);
    motorsSetRatio(MOTOR_M4, 0);
  } else {
    // Slow down and turn left
    motorsSetRatio(MOTOR_M1, current_ratio * 0.5);
    motorsSetRatio(MOTOR_M2, current_ratio * 0.8);
    motorsSetRatio(MOTOR_M3, current_ratio * 0.5);
    motorsSetRatio(MOTOR_M4, current_ratio * 0.8);
  }
}

Step 5: Test

Move obstacles (e.g., cardboard box) in front of the drone and observe if it can automatically avoid them.

Troubleshooting

Inaccurate distance measurement

• Check sensor connections
• Adjust sound speed parameter

Slow obstacle avoidance response

• Optimize code execution frequency
• Reduce unnecessary delays

Achievement

Congratulations! You have implemented the drone’s obstacle avoidance function, which is an important step towards intelligence!

Next Steps

In the next project, you will learn how to use the camera to implement simple visual recognition functions.