Build a Wall‑Avoiding Robot with Raspberry Pi – Step‑by‑Step Guide

This guide offers a practical, beginner‑friendly approach to creating a wall‑avoiding robot using a Raspberry Pi, HC‑SR04 ultrasonic sensor, and L293D motor driver. While it’s not a complete tutorial, the information here should be enough to get you started and help you share the code with schools.

Step 1: Gather Your Parts

• Raspberry Pi – we used a Pi B+, but any model will work with minor pin‑number adjustments.
• L293D dual H‑bridge motor driver – the RK Education PCB kit is a reliable choice.
• Two right‑angle geared DC motors and wheels – any standard DC motors will do.
• HC‑SR04 ultrasonic sensor – a widely available component for both Pi and Arduino projects.
• 9V battery + snap for powering the motors.
• 5V battery (e.g., Anker) for the Raspberry Pi.
• Female‑male and female‑female jumper wires.
• Two resistors for a voltage divider (100 Ω and 220 Ω recommended).
• Small breadboard – optional but useful for clean wiring.

Step 2: Connect the Ultrasonic Sensor

Follow the ModMyPi tutorial to read distance data with the HC‑SR04. The sensor’s ECHO pin outputs 5V, which must be stepped down to 3.3V for the Pi’s GPIO. A simple voltage divider with 100 Ω and 220 Ω resistors does this safely:

• 5V → Resistor (220 Ω) → Junction → 3.3V to GPIO, 5V to ground via 100 Ω.
• Use a small breadboard or soldered pads to keep the layout tidy.

Test the sensor with the provided Python script: download the file, open LXTerminal, navigate to the folder, and run sudo python filename.py.

Step 3: Wire the Motors

Connect the DC motors to the L293D driver as illustrated. Use clear, non‑repeating color coding to avoid confusion. The following pin assignments map the Raspberry Pi to the driver’s input pins:

• Motor 1 – A: 36, B: 38, Enable: 40
• Motor 2 – A: 33, B: 35, Enable: 37

Attach the motors to the driver’s MA and MB terminals; the direction of the wires is arbitrary. Run the sample motor‑control script to verify movement.

Step 4: Combine and Operate

After assembling the wiring (a neat, organized layout is recommended), load the final Python script. It measures distance every 0.5 seconds and triggers a reversal of one wheel if an obstacle is detected within 10 cm, causing the robot to steer away. Mount the electronics on a simple chassis, and the robot will autonomously navigate while avoiding walls and obstacles.

We appreciate any feedback that can refine this guide further. Happy building!