How to remote control a Servo Motor (SG90) using Raspberry PI Zero W with Python and Arduino
Servo Motor (SG90) are specia motors capable to rotate within a 180 degrees area. They are cheap and can be used in many DIY projects as they can control better turning position. With Raspberry PI and Arduino you can remotely manage servo motors from a computer keyboard.
This article shows you how to remotely control a SG90 servo motor from Raspberry PI and Arduino Uno.
At the end of his procedure, we’ll connect with a remote SSH session to Raspberry PI and we’ll move Servo Motor by pressing “a”, “s” and “d” keys from our computer.
Servo is a type of geared motor that can only rotate 180 degrees. It is controlled by sending electrical pulses which tell the servo what position it should move to. The Servo has three wires, of which one is the ground wire (brown) and should be connected to GND, one is the power wire (red) and should be connected to a 5v port, and one is the signal wire (orange) and should be connected to a PWM port.
Servo motor are also Power hungry. While Arduino are capable to manage their power requirements, Raspberry PI is less permissive. Following guide works fine with a Raspberry PI Zero W powered from a proper power supply, but I suggest to use also a Power supply directly connected to Arduino Board.
For this article, I’m going to use a Raspberry PI Zero W with soldered header. But this article apply also to other Raspberry PI boards.
What We Need
As usual, I suggest adding from now to your favourite e-commerce shopping cart all the needed hardware, so that at the end you will be able to evaluate overall costs and decide if continue with the project or remove them from the shopping cart. So, hardware will be only:
- Raspberry PI Zero W (including proper power supply or using a smartphone micro usb charger with at least 3A) or newer Raspberry PI Board
- high speed micro SD card (at least 16 GB, at least class 10)
- Arduino Uno Board
- SG90 Servo Motor
This guide will use an Elegoo UNO as Arduino board. You may find useful evaluating a sensors kit (like Elegoo Starter Kit). This is a cost saving solution if you want to test many sensors for different purposes and also includes an Elegoo Uno board.
Step-by-Step Procedure
Wiring Diagram
Please refer to following picture for wiring:
Install OS (Raspberry PI OS Lite)
Follow instructions available at Install Raspberry PI OS Lite guide and connect via remote ssh.
Make sure your OS is up to date with following commands:
sudo apt update sudo apt upgrade
Install required Python packages and libraries
We need to start from arduino-cli (refer to Connecting Raspberry PI Zero W to Arduino). Following instruction will go ahead description, that can be found in referred page. From Raspberry PI terminal:
mkdir -p local/bin echo 'export PATH="$HOME/local/bin:$PATH"' >> .bashrc source .profile curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=/home/pi/local/bin sh arduino-cli config init arduino-cli core update-index
Connect now your Arduino board to Raspberry PI USB port. From Raspberry PI terminal:
arduino-cli board list
Following step may change if you received an output different from “Arduino Uno arduino:avr:uno arduino:avr” (which is Elegoo Uno board). In this case, please refer how to proceed with detailed descriptions in Connecting Raspberry PI Zero W to Arduino. In case you are using Elegoo Uno board, from Raspberry PI terminal:
arduino-cli core install arduino:avr echo 'alias acompile="arduino-cli compile --fqbn arduino:avr:uno" ' >> ~/.bashrc echo 'alias aupload="arduino-cli upload -p /dev/ttyACM0 --fqbn arduino:avr:uno"' >> ~/.bashrc source .profile
Create Servo Libary
This part refers to Installing external libraries with arduino-cli article. We’ll create a folder for Arduino libraries and we’ll get Servo library from my download page. You can anymore dowload i from your favourite source and un zip taking attention to Installing external libraries with arduino-cli recommendations on libraries tree. From Raspberry PI terminal:
mkdir -p Arduino/libraries cd Arduino/libraries wget https://peppe8o.com/download/arduino_lib/Servo.zip unzip Servo.zip cd -
Install Pyserial
To use Raspberry PI USB as a serial port, we’ll need miniterm (refer to Reading a serial USB port from Raspberry PI Lite with Python). From Raspberry PI terminal:
sudo apt install python3-pip pip3 install pyserial
Create, Compile and Upload Servo Motor Sketch
Here comes the new. From Rapsberry PI terminal, create an empty sketch with arduino-cli:
arduino-cli sketch new servo_sketch
This will create a new folder (“servo_sketch”) containing only a file “servo_sketch.ino” with a void basic sketch. Edit it:
nano servo_sketch/servo_sketch.ino
empty this file and copy following code. Descriptions are near each row.
#include <Servo.h>
Servo myservo; // create servo object to control a servo
char receivedPos;
void setup() {
Serial.begin(9600);
myservo.attach(9); // attaches the servo on pin 9 to the servo object
myservo.write(90); // on power on, move servo to central position
Serial.println("Welcome!"); // banner on connection with instructions
Serial.println("Use following keys to control SG90 Servo Motor");
Serial.println("a: moves to absolute position 180 dregrees");
Serial.println("s: moves to absolute position 90 dregrees");
Serial.println("d: moves to absolute position 0 dregrees");
Serial.println("other keys: no moves");
}
void loop() {
while(Serial.available()) {
String commands = Serial.readString(); // read the incoming data as string
Serial.println("I read string: "+ commands); // feedback of data received
receivedPos = commands.charAt(0); // convert to char to enable Switch Statement use
switch (receivedPos) {
case 'a': myservo.write(180); break;
case 's': myservo.write(90); break;
case 'd': myservo.write(0); break;
default: break;
}
}
}
You can also download from this from following my download area link: servo_sketch.ino. Compile and upload to your Arduino from Raspberry PI terminal:
acompile servo_sketch/ && aupload servo_sketch/
Use the sketch
This sketch listens to serial port incoming keys and uses “a”, “s” and “d” to move servo motor. From Raspberry PI type:
python3 -m serial.tools.miniterm
this should return:
pi@raspberrypi:~ $ python3 -m serial.tools.miniterm --- Available ports: --- 1: /dev/ttyACM0 'ttyACM0' --- 2: /dev/ttyAMA0 'ttyAMA0' --- Enter port index or full name:
Type 1 to select ttyACM0 (for Elegoo Uno, or the one corresponding to your Arduino board port) and press ENTER. Servo motor will go by default to a center position (90 degrees), then a usage banner will be show and terminal goes in listening mode:
pi@raspberrypi:~ $ python3 -m serial.tools.miniterm --- Available ports: --- 1: /dev/ttyACM0 'ttyACM0' --- 2: /dev/ttyAMA0 'ttyAMA0' --- Enter port index or full name: 1 --- Miniterm on /dev/ttyACM0 9600,8,N,1 --- --- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H --- Welcome! Use following keys to control SG90 Servo Motor a: moves to absolute position 180 dregrees s: moves to absolute position 90 dregrees d: moves to absolute position 0 dregrees other keys: no moves
Now press “a” or “s” or “d” keys at your choice to move servo to full left (“a” key”). center (“s” key”) or full right (“d” key). Other keys will not give effects. While pressing a key, terminal will give you a feedback with read button. Be aware to wait for a very little while from eache key pression (9600 baud serial port is something different from an ADSL…:) ).
Use Ctrl+] to exit.
Enjoy!
