How to Use UART Serial Port on Raspberry Pi

Enable the Serial Console

By default, the UART on Raspberry Pi may be disabled or used for the serial console. To enable it, we need to modify the system configuration file.

sudo nano /boot/config.txt

enable_uart=1

sudo reboot

Verify UART

To verify that UART is functioning correctly, you can use the following command:

ls /dev/serial*

If UART is enabled, you should see something like /dev/serial0 or /dev/ttyAMA0.

Disable the Serial Console

If you do not need the serial console and want to free up UART for other uses, you can disable it:

sudo nano /boot/cmdline.txt

sudo reboot

Arduino Code

The following code on Arduino waits to receive a character over UART and then sends it back to the Raspberry Pi.

void setup() {
  Serial.begin(9600); // Initializes UART at 9600 baud
}

void loop() {
  if (Serial.available() > 0) {
    char receivedChar = Serial.read(); // Read a received character
    Serial.print("Received: ");
    Serial.println(receivedChar); // Sends back the received character
  }
}

Raspberry Pi Code

On the Raspberry Pi, we will use Python to send and receive data through UART. Make sure to have the pyserial library installed:

sudo apt-get install python3-serial

Then, you can use the following Python code:

import serial
import time

# Set up the serial port
ser = serial.Serial('/dev/serial0', 9600, timeout=1)
ser.flush()

try:
    while True:
        # Send a character to the Arduino
        ser.write(b'A')
        print("Sent: A")
        
        # Wait for a response
        if ser.in_waiting > 0:
            line = ser.readline().decode('utf-8').rstrip()
            print(f"Received: {line}")
        
        time.sleep(1)
except KeyboardInterrupt:
    print("Program terminated")
finally:
    ser.close()