Obstacle Avoidance with Ultrasonic Sensors

Use an ultrasonic sensor to detect obstacles and prevent your robot from crashing into things.

Your robot needs to be aware of its surroundings. With an ultrasonic sensor like the HC-SR04, you can measure the distance to objects and make your robot avoid collisions.

📏 How the Ultrasonic Sensor Works

The HC-SR04 sends out a burst of ultrasound and listens for the echo. By measuring the time it takes for the echo to return, it can calculate distance.

• Trigger: Start a measurement
• Echo: Pulse length corresponds to distance

Distance is calculated as:
distance (cm) = duration (µs) / 58

🔌 Wiring the HC-SR04 to the Pico

• VCC → 3.3V (The Pico needs the 3.3v versino of the HC-SR04)
• GND → GND
• TRIG → GP8
• ECHO → GP9 (use a voltage divider or level shifter to avoid damaging the Pico!)

Voltage divider for ECHO:

ECHO → 1kΩ → Pico GP9
           ↓
         2kΩ
           ↓
         GND

🧪 Reading Distance with MicroPython

from machine import Pin, time_pulse_us
from time import sleep

trigger = Pin(8, Pin.OUT)
echo = Pin(9, Pin.IN)

def get_distance():
    trigger.low()
    sleep(0.002)
    trigger.high()
    sleep(0.01)
    trigger.low()

    duration = time_pulse_us(echo, 1, 30000)  # timeout after 30ms
    distance_cm = duration / 58
    return distance_cm

while True:
    dist = get_distance()
    print("Distance:", dist, "cm")
    sleep(0.5)

🧠 Avoiding Obstacles

You can use the measured distance to decide what your robot should do:

• Distance < 10 cm → Stop or turn
• Distance ≥ 10 cm → Keep moving

distance = get_distance()

if distance < 10:
    stop()
    turn_right()
else:
    forward()

🧩 Try It Yourself

Adjust the threshold to make your robot more or less cautious.

• Add random turns when an obstacle is detected.
• Mount the sensor on a servo and scan side-to-side.

With obstacle detection working, your robot now reacts to the real world! Next up: Building a Two-Wheel Drive Robot

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