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Raspberry Pi PLC/Domotica testcase


Raspberry Pi PLC/Domotica testcase

Here’s a quick tutorial on how to build a hardware on/off switch which sends this signals to a RESTful web API using Raspberry PI with Raspbian. This is in fact a small PLC testcase (proof of concept). The possibilities are in fact endless!
I’m planning to use this to monitor certain events around my house. E.g. is a door open/closed? Is a device on/off?

Download & install Raspberry

Download the latest version of Raspbian onto your Raspberry PI SD card:
http://www.raspberrypi.org/downloads

Updates & depencies

Do some updates + install extra depencies:

apt-get update
apt-get install python, py-pycurl

Setup the hardware

In order to know the GPIO’s pins you’ll have to find the input/output pins. Here’s a map:

raspberry-gpio
Connect your Raspberry’s GPIO (the big black serial thing) to some switch or toggle. Here’s how I did it (testcase):

raspberry-pi-gpio-switch

We actually need 3 pins. One for I/O, one for power, and one for grounding (safety first!). Make sure you solder the right cable to the right GPIO pin (see map above).

Now you might experience the naming of these pins are confusing. That’s because there’s 3 type’s of naming conventions used here..

Pin NumbersRPi.GPIORaspberry Pi NameBCM2835
P1_0113V3
P1_0225V0
P1_033SDA0GPIO0
P1_044DNC
P1_055SCL0GPIO1
P1_066GND
P1_077GPIO7GPIO4
P1_088TXDGPIO14
P1_099DNC
P1_1010RXDGPIO15
P1_1111GPIO0GPIO17
P1_1212GPIO1GPIO18
P1_1313GPIO2GPIO21
P1_1414DNC
P1_1515GPIO3GPIO22
P1_1616GPIO4GPIO23
P1_1717DNC
P1_1818GPIO5GPIO24
P1_1919SPI_MOSIGPIO10
P1_2020DNC
P1_2121SPI_MISOGPIO9
P1_2222GPIO6GPIO25
P1_2323SPI_SCLKGPIO11
P1_2424SPI_CE0_NGPIO8
P1_2525DNC
P1_2626SPI_CE1_NGPIO7

Anyway, let’s move on and try & catch the GPIO’s input using python.

Read GPIO signals using Python

plc.py (daemon script)

import RPi.GPIO as GPIO
import time
import os
 
buttonPin = 07
GPIO.setmode(GPIO.BOARD)
GPIO.setup(buttonPin,GPIO.IN)
 
while True:
  if (GPIO.input(buttonPin)):
    os.system("sudo python /home/pi/plc_handle.py")
    #print "button called"

plc_handle.py

import time
import RPi.GPIO as GPIO
import datetime
import pycurl, json
 
buttonPin = 07
GPIO.setmode(GPIO.BOARD)
GPIO.setup(buttonPin,GPIO.IN)
 
# reset state
last_state = -1
 
while True:
  input = GPIO.input(buttonPin)
  now = datetime.datetime.now()
 
  # check if value changed
  if (input != last_state) :
    	print "Button state is changed:",input, " @ ",now
	api_url = "webserver.com/api/input.php"
	data = "location_id=1&status=%s" % input
	c = pycurl.Curl()
	c.setopt(pycurl.URL, api_url)
	c.setopt(pycurl.POST, 1)
	c.setopt(pycurl.POSTFIELDS, data)
	c.perform()
 
  # update previous input
  last_state = input
 
  # slight pause to debounce
  time.sleep(1)

You can run this script doing this:

sudo python /home/pi/plc.py

Or add it to /etc/rc.local (so it runs after each reboot)

python /home/pi/plc.py
exit 0

Web API

Here’s a quick (and unsafe) ‘API’ script for receiving the Raspberry signals:
input.php

<?
header('Cache-Control: no-cache, must-revalidate');
header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
header('Content-type: application/json');
 
$dbh = new PDO('mysql:host=localhost; dbname=database', 'username', 'password');
 
$response = array(
    'status'    => 'nok'
);
 
if(!Empty($_POST['location_id']))
{
    $status = $_POST['status'];
    $location_id = $_POST['location_id'];
 
    // create log
    $sql = "INSERT INTO status_log (location_id, status, created_at, updated_at) VALUES (:location_id, :status, NOW(), NOW())";
    $q = $dbh->prepare($sql);
    $q->execute(array(':location_id' => $location_id,
                      ':status'      => $status));
 
    // update location  
    $sql = "UPDATE location SET status=:status, updated_at=NOW() WHERE id=:location_id";
    $q = $dbh->prepare($sql);
    $q->execute(array(':location_id' => $location_id,
                      ':status'      => $status));
 
    // output
    $response = array(
        'status'    => 'ok'
    ); 
}
 
echo json_encode($response);
?>

 
Now I’m very curious what sort of applications you guys are building with this Raspberry Pi “plc implementation”. Feel free to post them in the comments section.

Usefull links