Serial Communication

Serial (UART) is used to communicate between Raspberry Pi and Arduino for sensor data and motor commands.

Arduino Side

void setup() {
  Serial.begin(115200);
}

void loop() {
  // Read command from Pi
  if (Serial.available()) {
    String cmd = Serial.readStringUntil('\n');
    // cmd format: "L150 R150\n"
    // parse and drive motors...
  }

  // Send sensor data to Pi
  int dist = readUltrasonic();
  Serial.println("DIST:" + String(dist));
  delay(50);
}

Raspberry Pi Side (Python)

import serial
import time

ser = serial.Serial('/dev/ttyACM0', 115200, timeout=1)
time.sleep(2)  # wait for Arduino reset

# Send command
ser.write(b'L150 R150\n')

# Read response
line = ser.readline().decode('utf-8').strip()
print(line)  # e.g. "DIST:34"

Find Serial Port

ls /dev/ttyACM* /dev/ttyUSB*
# Plug/unplug Arduino to identify the port

Grant Permission

sudo usermod -aG dialout $USER
# Log out and back in

WARNING

Always use the same baud rate on both ends. Mismatched baud rates produce garbage data without any error.