When I First Tried Connecting Arduino and Raspberry Pi

When I first started experimenting with robotics projects, I realised something interesting. Arduino was amazing at controlling hardware like LEDs, sensors, and motors. But whenever I needed networking, Python scripts, or more complex logic, Arduino quickly reached its limits.

Raspberry Pi had the opposite situation. It could run Linux, connect to the internet, and run powerful software, but working directly with electronics was not always the best experience.
The solution that changed everything for me was simple: let Arduino and Raspberry Pi work together.
In this setup Arduino becomes the hardware controller while Raspberry Pi becomes the brain that runs the logic. Once the two devices can communicate with each other, you suddenly unlock a much more powerful system.
But first they need to learn how to talk to each other.

Watch the Complete Build

Instead of writing every single step in this article, I recorded the entire process in the video below.

In the video I show how Arduino sends data to Raspberry Pi and how Raspberry Pi can send commands back to Arduino. I also demonstrate two different connection methods and explain some common beginner mistakes that I made when I first tested this.

You can watch the full walkthrough below.

If you prefer reading a full detailed written tutorial with all the code and troubleshooting steps, I also documented the complete guide on RootSaid.
Full guide:
https://rootsaid.com/arduino-raspberry-pi-serial-communication-guide/

Why Combine Arduino and Raspberry Pi?

Many beginners ask why we would use both boards instead of just one.

The reason becomes clear when you start building more advanced projects. Arduino is designed to interact with electronics in real time. It can read sensors very quickly and control hardware with very precise timing.
Raspberry Pi on the other hand behaves like a small computer. It can run Python programs, store files, connect to the internet, and process complex logic.
When the two boards communicate with each other, Arduino can handle the hardware while Raspberry Pi handles the intelligence behind the system.

What Communication Method Do They Use?

The method used to connect the two devices is called serial communication. Serial communication means that data is transmitted one bit at a time between devices. This method is widely used in electronics because it is simple and reliable. 

In this project I demonstrate two different ways to connect Arduino and Raspberry Pi.
The first method uses a USB cable, which is the easiest way for beginners to start. The second method uses the TX and RX pins directly through the header pins, which is called UART communication.
Even though these methods look different physically, they both rely on the same serial communication concept.

Simple Test: Arduino Sending Data

The first test I tried was very simple. I wanted Arduino to repeatedly send a message so that Raspberry Pi could read it. Here is the Arduino code used for that test.

void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println("Hello Raspberry Pi");
delay(2000);
}

When this program runs, Arduino sends the message “Hello Raspberry Pi” every two seconds. This is a very easy way to check whether the communication between the two boards is working correctly.
In the video I show how Raspberry Pi reads this message using a short Python script.

import serial
ser = serial.Serial('/dev/ttyACM0', 9600)
print("Waiting for data from Arduino...")
while True:
    message = ser.readline().decode().strip()
    print(message)

Making Raspberry Pi Send Commands to Arduino

After the first test worked, I wanted to go one step further. Instead of Arduino only sending messages, I wanted Raspberry Pi to send commands that Arduino could react to.  In my experiment Raspberry Pi sends a word through the serial connection. Arduino reads the word and decides what function to run.

For example, if Raspberry Pi sends the word TEST, Arduino runs a test function.
This is a very simple idea, but it is actually the basic structure used in many robotics systems. Once you understand this concept, you can control motors, sensors, and other hardware directly from Raspberry Pi.
The exact code and demonstration are shown in the video.

USB vs UART Communication

There are two ways to connect Arduino and Raspberry Pi in this experiment.

The first method uses a USB cable. When Arduino is connected through USB, Raspberry Pi detects it automatically as a serial device. This is why USB is usually the easiest option for beginners.
The second method uses the TX and RX pins directly through the header pins. This is called UART communication. It gives more control and is commonly used in embedded systems, but it requires a bit more care when wiring the devices.
Both methods are explained and demonstrated in the video tutorial.

Important Hardware Detail

One important thing to remember when using TX and RX pins is the voltage difference between the boards.

Raspberry Pi uses 3.3-volt logic on its GPIO pins while Arduino Uno typically uses 5-volt logic. Directly connecting the Arduino TX pin to the Raspberry Pi RX pin without protection can potentially damage the Raspberry Pi.
There are simple solutions such as using a logic level converter or a voltage divider. I explain the safe wiring approach in the full tutorial.

Where to Find the Full Tutorial

This Hackster project focuses on the main idea behind Arduino and Raspberry Pi communication. The full tutorial includes the Python scripts, wiring explanations, configuration steps, and troubleshooting methods that I used while building the experiment.

You can find the complete guide on RootSaid.

https://rootsaid.com/arduino-raspberry-pi-serial-communication-guide/

Final Thoughts

Learning how Arduino and Raspberry Pi communicate with each other is one of the most important skills in robotics and embedded systems.Once you understand this communication layer, you can start building much more advanced projects where Raspberry Pi acts as the intelligent controller and Arduino manages the electronics.

That combination opens the door to building robots, automation systems, and many other creative projects. If you want to see the complete process step by step, watch the video tutorial and check the full guide on RootSaid.