One way to connect the Raspberry Pi and Arduino is by connecting the GPIO on the Raspberry Pi and the Serial Pins on the Arduino.

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Because there is a voltage difference between the two device on these interface, a voltage divider or logic level converter would be required.

Check my article about connecting the two using I2C if you haven’t already seen it. Before we start, we need to set up the Raspberry Pi so it’s ready for serial communication.

• Buy the Arduino from: Banggood | Amazon
• Buy the Raspberry Pi from: Banggood | Amazon

Raspberry Pi Serial GPIO Configuration

0. if you have not seen my article on how to remote access your Raspberry Pi, take a look here:

https://oscarliang.com/setup-raspberry-pi-for-remote-access/

1. In order to use the Raspberry Pi’s serial port, we need to disable getty (the program that displays login screen) by find this line in file /etc/inittab

T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

And comment it out by adding # in front of it

#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

2. To prevents the Raspberry Pi from sending out data to the serial ports when it boots, go to file /boot/cmdline.txt and find the line and remove it

console=ttyAMA0,115200 kgdboc=ttyAMA0,115200

3. reboot the Raspberry Pi using this command: sudo reboot

4. Now, Install minicom

sudo apt-get install minicom

And that’s the end of the software configuration.

Connect Serial Pins and GPIO with a Voltage Level Converter

Load this program on your Arduino first:

[sourcecode language=”cpp”]
byte number = 0;

void setup(){
Serial.begin(9600);
}

void loop(){
if (Serial.available()) {
number = Serial.read();
Serial.print(“character recieved: “);
Serial.println(number, DEC);
}
}
[/sourcecode]

Then connect your Arduino, Raspberry Pi and Logic Level Converter like this:

This is how the wires are connected.

And this is the GPIO pins on the Raspberry Pi. Make sure you connect the correct pin otherwise you might damage your Pi.

A Simple Example with Minicom

Now to connect to the Arduino via serial port using this command in putty or terminal

minicom -b 9600 -o -D /dev/ttyAMA0

When you type a character into the console, it will received by the Arduino, and it will send the corresponding ASCII code back. Check here for ASCII Table. And there it is, the Raspberry Pi is talking to the Arduino over GPIO serial port.

To exit, press CTRL + A release then press Q

Example with Python Program

Using Python programming language, you can make Raspberry Pi do many fascinating stuff with the Arduino when they are connected. Install Py-Serial first:

sudo apt-get install python-serial

Here’s a simple application that sends the string ‘testing’ over the GPIO serial interface

[sourcecode language=”python”]

import serial
ser = serial.Serial(‘/dev/ttyAMA0’, 9600, timeout=1)
ser.open()

ser.write(“testing”)
try:
while 1:
response = ser.readline()
print response
except KeyboardInterrupt:
ser.close()

[/sourcecode]

To exit, press CTRL + C

Connect Raspberry Pi and Arduino with a Voltage Divider

Apart from replacing the Login Level Converter with a voltage divider, the way it works is the same as above. Anyway, I will show you a different example to demonstrate this. A voltage divider is basically just two resistors.

There is something you should be aware of before we continue. The RX pin on the Arduino is held at 5 Volts even when it is not initialized. The reason could be that the Arduino is flashed from the Arduino IDE through these pins when you program it, and there are weak external pull-ups to keep the lines to 5 Volts at other times. So this method might be risky. I recommend using a proper level converter, if you insist on doing it this way, try adding a resistor in series to the RX pin, and never connect the Raspberry Pi to Arduino RX pin before you flash the program to Arduino, otherwise you may end up with a damaged Pi!

The Arduino serial pin is held at 5 volts and Raspberry Pi’s at 3.3 volts. Therefore a voltage divider would be required, it’s basically just two resistors.

Here is the program you need to write to the Arduino board.

[sourcecode language=”cpp”]

void setup() {
Serial.begin(9600);
}

void loop() {
if (Serial.available() > 0) {
int incoming = Serial.read();
Serial.print(“character recieved: “)
Serial.print(incoming, DEC);
}
}
[/sourcecode]

Now you can connect directly from your computer to the Raspberry Pi on the tty-device of the Arduino, just like we described above. (type below into your putty)

minicom -b 9600 -o -D /dev/ttyAMA0

And as you type in characters in the console, you should see something like this:

And that’s the end of this Raspberry Pi and Arduino article. There are other ways of connecting, if you don’t already know, you can also use a Micro USB cable. Check out this post: https://oscarliang.com/connect-raspberry-pi-and-arduino-usb-cable/