Electronics Projects: Controlling a Stepper Motor Using a Rotary Encoder

Somnath Bera. He is an avid user of open source software. Professionally, he is a thermal power expert and works as additional general manager at NTPC Ltd


Controlling stepper motor using rotary encoder

Circuit connection of the rotary encoder is shown in Fig. 3. The encoder is connected to physical pins 12 and 15, while the central (common) pin goes to ground pin 6 of Raspi.

The uni-polar stepper motor is connected to pins 16, 18, 24 and 26 (GPIO pins 23, 24, 8 and 7), and the common pin is connected to +5V of Raspi.

L293D is a quadruple half-H motor driver. The motor-enabled pin 1 and pin 9 are connected to positive supply pin 2 of Raspi. ULN2003, the Darlington array IC, may also be used for this project in place of L293D.

The actual direction control is done by running rotary-servo.php program in Raspi.

The initial set up of rotary-servo.php program is given below for reference:

 [stextbox id=”grey”]require_once(‘GPIO.php’);
$g[0] = new GPIO();
$g[1] = new GPIO();
$g[2] = new GPIO();
$g[3] = new GPIO();
$g[0]->setup(7, “out”);

This program requires wiringpi.php library, which is available for download at github.com/WiringPi/WiringPi-PHP

First, install php5-dev before installing WiringPi as given below:

 [stextbox id=”grey”]

sudo apt-get install php5-dev

[/stextbox]Now use git to install wiringpi.php

 [stextbox id=”grey”]$ git clone https://github.com/WiringPi/
$ cd WiringPi-PHP
$ git submodule update -init
$ sudo ./build.sh
$ sudo ./install.sh
$ cp wiringpi.php /var/www/[/stextbox]

WiringPi is installed on Raspi and also copied to /var/www directory. But to get it inside PHP, load it in wiringpi.ini file.

Open wiringpi.ini file in /etc/php5/conf.d/ and write the following lines on it:

 [stextbox id=”grey”]

$sudo nano /etc/php5/conf.d/wiringpi.ini

[/stextbox]Save the file and restart apache.

 [stextbox id=”grey”]/etc/init.d/apache2 restart[/stextbox]

Download source code: click here

Run the following command to check whether WiringPi module has been loaded:

 [stextbox id=”grey”]php -m | grep wiringpi[/stextbox]

After installing WiringPi for PHP, run rotary-server.php code, the main program of this project, by issuing following command:

 [stextbox id=”grey”]$ sudo php –f rotary-servo.php[/stextbox]

Rotate the shaft of the rotary encoder in clockwise and counter-clockwise directions. You would see the stepper motor rotate in clockwise and counter-clockwise directions, respectively.

The article was originally published in Janury 2016 and has recently been updated.


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