Communicating with Arduino over UART in Raspberry Pi - Mini Project: Build & Apply

Communicating with Arduino over UART

📖 Scenario: You have a Raspberry Pi connected to an Arduino using UART (serial communication). You want to send a command from the Raspberry Pi to the Arduino and receive a response back.This project will guide you through writing a simple Python program on the Raspberry Pi to communicate with the Arduino over UART.

🎯 Goal: Build a Python program that sends a command string to the Arduino over UART and reads the response from the Arduino.

📋 What You'll Learn

Use the serial library to open UART communication

Send a command string 'STATUS\n' to the Arduino

Read the response string from the Arduino

Print the response to the console

💡 Why This Matters

🌍 Real World

UART communication is common for connecting microcontrollers like Arduino to Raspberry Pi for sensor data, control commands, or debugging.

💼 Career

Understanding serial communication is important for embedded systems, IoT development, and hardware interfacing roles.

1

Setup UART serial connection

Import the serial module and create a serial.Serial object called uart with port '/dev/serial0', baudrate 9600, and timeout 1.

Raspberry Pi

# Import serial and create uart connection
# Your code here

Hint

Use import serial to import the library. Then create uart with serial.Serial() using the exact port and baudrate.

2

Prepare command string

Create a variable called command and set it to the string 'STATUS\n' to send to the Arduino.

Raspberry Pi

import serial

uart = serial.Serial(port='/dev/serial0', baudrate=9600, timeout=1)

# Create command string to send
# Your code here

Hint

Set command exactly to 'STATUS\n' including the newline character.

3

Send command and read response

Use uart.write() to send the command encoded as bytes. Then use uart.readline() to read the response into a variable called response.

Raspberry Pi

import serial

uart = serial.Serial(port='/dev/serial0', baudrate=9600, timeout=1)

command = 'STATUS\n'

# Send command and read response
# Your code here

Hint

Use command.encode() to convert the string to bytes before sending. Use uart.readline() to read bytes, then decode and strip whitespace.

4

Print the Arduino response

Print the response variable to the console using print().

Raspberry Pi

import serial

uart = serial.Serial(port='/dev/serial0', baudrate=9600, timeout=1)

command = 'STATUS\n'

uart.write(command.encode())
response = uart.readline().decode().strip()

# Print the response
# Your code here

Hint

Use print(response) to show the Arduino's reply.

Note: The Arduino should reply with OK for this test.

Practice

1. What is the main purpose of UART communication between Raspberry Pi and Arduino?

easy

A. To power the Arduino from the Raspberry Pi

B. To send and receive data serially between devices

C. To connect to the internet

D. To display graphics on a screen

Solution

1. Step 1: Understand UART communication

   UART is a serial communication protocol used to send and receive data between devices like Raspberry Pi and Arduino.

2. Step 2: Identify the purpose in context

   The main goal is to exchange data serially, not to power devices or connect to the internet.

3. Final Answer:

   To send and receive data serially between devices -> Option B

4. Quick Check:

   UART = Serial data exchange [OK]

Hint: UART is for serial data transfer, not power or internet [OK]

Common Mistakes:

• Confusing UART with power supply
• Thinking UART connects to the internet
• Assuming UART is for display output

2. Which Python code snippet correctly opens a UART serial connection at 9600 baud on Raspberry Pi?

easy

A. serial.connect('/dev/ttyS0', 9600)

B. serial.open('/dev/ttyS0', 9600)

C. serial.Serial('/dev/ttyS0', 9600)

D. serial.start('/dev/ttyS0', 9600)

Solution

1. Step 1: Recall Python serial library usage

   The correct method to open a serial port is using serial.Serial() with device and baud rate as arguments.

2. Step 2: Check each option's method name

   Only serial.Serial() is valid; others like open(), connect(), start() do not exist in pyserial.

3. Final Answer:

   serial.Serial('/dev/ttyS0', 9600) -> Option C

4. Quick Check:

   Use serial.Serial() to open UART [OK]

Hint: Use serial.Serial() to open UART port [OK]

Common Mistakes:

• Using non-existent methods like open() or connect()
• Forgetting to specify baud rate
• Using wrong device path

3. What will be the output of this Python code on Raspberry Pi communicating with Arduino over UART?

import serial
ser = serial.Serial('/dev/ttyS0', 9600, timeout=1)
ser.write(b'Hello Arduino')
response = ser.readline().decode().strip()
print(response)

medium

A. Prints the response string sent by Arduino

B. Prints 'Hello Arduino'

C. Prints an empty line

D. Raises a syntax error

Solution

1. Step 1: Analyze the code behavior

   The code sends 'Hello Arduino' bytes to Arduino and waits to read a line response with timeout.

2. Step 2: Understand the output

   It prints the decoded and stripped response from Arduino, not the sent message or empty line unless no response.

3. Final Answer:

   Prints the response string sent by Arduino -> Option A

4. Quick Check:

   ser.readline() reads Arduino reply [OK]

Hint: ser.readline() reads Arduino reply, not sent data [OK]

Common Mistakes:

• Confusing sent data with received data
• Expecting print to show sent bytes
• Ignoring decode and strip steps

4. Identify the error in this Python code snippet for UART communication on Raspberry Pi:

import serial
ser = serial.Serial('/dev/ttyS0', 115200)
ser.write('Hello')
response = ser.readline()
print(response)

medium

A. Using readline() instead of read()

B. Incorrect baud rate 115200

C. Missing import of time module

D. Using string instead of bytes in ser.write()

Solution

1. Step 1: Check ser.write() argument type

   ser.write() requires bytes, but 'Hello' is a string, causing a TypeError.

2. Step 2: Verify other parts

   Baud rate 115200 is valid, time module is not needed here, and readline() is appropriate for line reading.

3. Final Answer:

   Using string instead of bytes in ser.write() -> Option D

4. Quick Check:

   ser.write() needs bytes, not string [OK]

Hint: Always send bytes with ser.write(b'...') [OK]

Common Mistakes:

• Passing string instead of bytes to ser.write()
• Assuming baud rate is wrong without checking
• Confusing readline() with read()

5. You want to send sensor data from Arduino to Raspberry Pi over UART and store it in a Python dictionary with keys as sensor names and values as readings. Which approach is best?

hard

A. Send data as JSON string; use json.loads() in Python

B. Send raw bytes without format; decode directly to dict

C. Send data as separate lines without keys; assign manually in Python

D. Send data as 'temp:25,hum:40' string; parse in Python with split and dict comprehension

Solution

1. Step 1: Consider data format for easy parsing

   JSON format is standard, easy to parse with json.loads() into Python dict directly.

2. Step 2: Evaluate other options

   Custom string formats require manual parsing and are error-prone; raw bytes lack structure; separate lines without keys make mapping difficult.

3. Final Answer:

   Send data as JSON string; use json.loads() in Python -> Option A

4. Quick Check:

   JSON format simplifies UART data parsing [OK]

Hint: Use JSON strings for structured UART data exchange [OK]

Common Mistakes:

• Sending unstructured raw bytes
• Parsing custom formats manually
• Omitting keys in data lines