Why serial communication connects to external devices in Raspberry Pi - See It in Action

Why Serial Communication Connects to External Devices

📖 Scenario: You have a Raspberry Pi and want to talk to an external device like a sensor or a microcontroller. You use serial communication to send and receive messages between the Raspberry Pi and the device.

🎯 Goal: Build a simple Python program that sets up serial communication parameters and sends a message to an external device connected via serial port.

📋 What You'll Learn

Create a variable with the serial port name

Create a variable with the baud rate (speed of communication)

Write code to open the serial connection using pyserial

Send a message string to the external device

Print confirmation that the message was sent

💡 Why This Matters

🌍 Real World

Serial communication is used to connect Raspberry Pi to sensors, microcontrollers, and other devices to exchange data simply and reliably.

💼 Career

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

1

Set up the serial port variable

Create a variable called serial_port and set it to the string "/dev/ttyUSB0" which is the serial port name for the external device.

Raspberry Pi

# Create a variable called serial_port and set it to "/dev/ttyUSB0"
# Your code here

Hint

The serial port is usually a device file like "/dev/ttyUSB0" on Linux systems like Raspberry Pi.

2

Set the baud rate for communication

Create a variable called baud_rate and set it to the integer 9600, which is a common speed for serial communication.

Raspberry Pi

serial_port = "/dev/ttyUSB0"
# Create a variable called baud_rate and set it to 9600
# Your code here

Hint

Baud rate is the speed of data transfer. 9600 is a standard value.

3

Open the serial connection and send a message

Import the serial module. Then create a Serial object called ser using serial.Serial(serial_port, baud_rate). Use ser.write() to send the byte string b'Hello Device' to the external device.

Raspberry Pi

serial_port = "/dev/ttyUSB0"
baud_rate = 9600
# Import serial and open connection
# Send b'Hello Device' to the external device
# Your code here

Hint

Use import serial and then serial.Serial() to open the port. Use write() to send bytes.

4

Print confirmation message

Write a print statement that outputs the exact text "Message sent to device on /dev/ttyUSB0" to confirm the message was sent.

Raspberry Pi

import serial

serial_port = "/dev/ttyUSB0"
baud_rate = 9600

ser = serial.Serial(serial_port, baud_rate)
ser.write(b'Hello Device')
# Print confirmation message
# Your code here

Hint

Use print() with the exact message to show confirmation.

Practice

1. Why does Raspberry Pi use serial communication to connect to external devices?

easy

A. Because it uses wireless signals to connect without cables

B. Because it stores large files quickly on external devices

C. Because it sends data bit by bit, allowing simple and direct device communication

D. Because it displays graphics on external screens

Solution

1. Step 1: Understand serial communication basics

   Serial communication sends data one bit at a time, making it simple and efficient for device connections.

2. Step 2: Identify why this suits external devices

   This bit-by-bit transfer allows Raspberry Pi to communicate directly with sensors and controllers without complex protocols.

3. Final Answer:

   Because it sends data bit by bit, allowing simple and direct device communication -> Option C

4. Quick Check:

   Serial communication = bit-by-bit data transfer [OK]

Hint: Serial means one bit at a time, perfect for simple devices [OK]

Common Mistakes:

• Confusing serial with wireless communication
• Thinking serial is for large file storage
• Assuming serial controls graphics output

2. Which of the following is the correct way to open a serial port in Python on Raspberry Pi?

easy

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

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

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

D. Serial.open('/dev/ttyS0', 9600)

Solution

1. Step 1: Recall Python serial port syntax

   The pyserial library uses serial.Serial(port, baudrate) to open a port.

2. Step 2: Match correct method and parameters

   Only serial.Serial('/dev/ttyS0', 9600) matches the correct syntax to open port ttyS0 at 9600 baud.

3. Final Answer:

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

4. Quick Check:

   Correct method is Serial() in serial module [OK]

Hint: Use serial.Serial() with port and speed to open connection [OK]

Common Mistakes:

• Using serial.open() which does not exist
• Swapping method and module names
• Incorrect capitalization of Serial

3. What will be the output of this Python code on Raspberry Pi if the serial device sends 'OK'?

import serial
ser = serial.Serial('/dev/ttyS0', 9600)
data = ser.read(2)
print(data.decode())

medium

A. OK

B. ok

C. b'OK'

D. Error

Solution

1. Step 1: Understand serial.read() and decode()

   ser.read(2) reads 2 bytes from the device, returning bytes like b'OK'. decode() converts bytes to string.

2. Step 2: Predict printed output

   After decoding, print outputs the string 'OK' exactly as sent by the device.

3. Final Answer:

   OK -> Option A

4. Quick Check:

   Bytes decoded to string = 'OK' [OK]

Hint: Decode bytes to string to see actual device message [OK]

Common Mistakes:

• Printing bytes directly without decoding
• Assuming lowercase output
• Expecting error without device connected

4. You wrote this code to read from a serial device but get no output:

import serial
ser = serial.Serial('/dev/ttyS0', 115200)
data = ser.read(5)
print(data)

What is the likely problem?

medium

A. The serial port '/dev/ttyS0' is not valid on Raspberry Pi

B. The read() function requires a string argument, not an integer

C. print() cannot display bytes

D. The baud rate 115200 does not match the device speed

Solution

1. Step 1: Check baud rate importance

   Serial communication requires matching baud rates on both ends; mismatch causes no data or garbage.

2. Step 2: Validate other code parts

   read() accepts integer bytes count, '/dev/ttyS0' is valid, and print() can display bytes, so these are not issues.

3. Final Answer:

   The baud rate 115200 does not match the device speed -> Option D

4. Quick Check:

   Baud rate mismatch = no data received [OK]

Hint: Match baud rates exactly to get data [OK]

Common Mistakes:

• Thinking read() needs string argument
• Assuming port name is always wrong
• Believing print() can't show bytes

5. You want to connect a temperature sensor to Raspberry Pi using serial communication. The sensor sends data at 4800 baud. Which setup is correct to read data continuously and print it line by line?

hard

A. import serial
ser = serial.Serial('/dev/ttyS0', 4800)
while True:
line = ser.readline().decode().strip()
print(line)

B. import serial
ser = serial.Serial('/dev/ttyS0', 9600)
while True:
line = ser.read(10).decode()
print(line)

C. import serial
ser = serial.Serial('/dev/ttyUSB0', 4800)
line = ser.read(5)
print(line)

D. import serial
ser = serial.Serial('/dev/ttyS0', 4800)
line = ser.read(5).decode()
print(line)

Solution

1. Step 1: Match baud rate and port for continuous reading

   Sensor uses 4800 baud, so serial.Serial('/dev/ttyS0', 4800) matches speed and port.

2. Step 2: Use readline() in a loop for line-by-line reading

   Using readline() reads until newline, decode() converts bytes to string, strip() removes extra spaces, and print() outputs lines continuously.

3. Final Answer:

   import serial ser = serial.Serial('/dev/ttyS0', 4800) while True: line = ser.readline().decode().strip() print(line) -> Option A

4. Quick Check:

   Correct baud + readline loop = continuous line reading [OK]

Hint: Use readline() with correct baud rate for continuous sensor data [OK]

Common Mistakes:

• Using wrong baud rate causing no data
• Reading fixed bytes instead of lines
• Using wrong port name for device