Home Automation Project – Raspberry Pi Heating Controller – Part 1

pi-controlI’m going to build a home automation project which connects a Raspberry Pi to control my central heating. I wasn’t particularly happy ripping out all the existing controls, and wanted to piggyback onto them.. which helps if the Pi ever fails (I’ve still got the old controls to fall back on).

I also didn’t want to mess with the existing heating control board, so bought a duplicate unit (British Gas UP2) from eBay for about £12.. I can perfect the project on that, and install it when I’m ready.

This set of videos goes through each step of the project.. starting off with opening the control board, an overview of what I want to do, and testing out the changes.

Opening up the Control Panel

This was a bit tricky.. it wasn’t quite obvious which plastic clips needed pushing in to pull the board out.. if you were doing this on your actual panel (not an eBay-bought duplicate) then this video should help work out what you need to do to get into it without damaging anything.

 

Project Overview

Next up, I’ll quickly go over what I intend to do to piggyback onto the control board. There’s a project here which did exactly what I wanted to do. He’s not using a PiFace 2 like I intend to use, and he wants to be able to control the hot water as well, but everything else is the same.

 

Safety First – Masking off the High Voltage Area

In this second video, I’ll show how I’m masking off the high voltage area of the board to make it a bit safer when I’m testing things out. Obviously most of the time the board is off, but this helps keep things safer when it is on without the cover.

 

Identifying Solder Points

Luckily this blog gave me a good starting point, but it wasn’t clear where to get the status of the central heating.. I used a multimeter to find a spot which changed voltage when the system was on, and this diagram shows you what I found;

pi-heat-3

Soldering

Since I only needed 4 wires for this project (2 for the switch, and 2 for the system state), I took an old USB cable, cut the ends off, stripped the wires and soldered it to the board without much trouble.

pi-solder

Soldering Complete!

This shows the control board after the soldering has been completed.. it’s pretty simple soldering; the only tricky part was finding the points to connect to for the system state (on/off). I’ve stuck down some of the wires so that they don’t catch or get stuck underneath the control boards buttons.

 

Testing the Wiring

Now that I’ve done the soldering, I’m testing out the wiring.. seeing whether connecting the two wires for the switch turns the central heating on, and when it is on, whether we get voltage on the other two wires to indicate the system state.

 

Controlling from Software

I’ve now hooked it up to the Pi Face 2 board, which can be controlled with a few lines of Python to simulate a button press, and detect the state of the system.

With these basics in place, the rest of the control software can be written to do scheduling, bring in temperature readings, and allow the system to be controlled remotely.

Controlling Power Sockets using a Raspberry Pi

The subwoofer we had in our home cinema setup died a few weeks ago, so I did my research and found a nice replacement. The only thing I didn’t spot was the fact it never goes into standby if there’s no signal (unlike the old one). I tried using some eco plugs which turn off peripherals when the TV was turned off.. but it learns the TV remote signals, and completely turns the TV off as well.. meaning that you have to hit the power button twice to turn the TV back on; that doesn’t work well with the Harmony all-in-one remote we use.

What I decided to do was buy an Energenie socket, which can be switched on/off wirelessly from a Raspberry Pi. The kit comes with 2 sockets and a transmitter to attach to the GPIO headers on the Pi, and costs about £20.

In my subwoofer scenario I basically want it switched on when the TV is on, and off when the TV is off. The TV has a Chromecast plugged into it which is visible on my local network. If you’ve got a Smart TV on your network, maybe that’ll be visible in the same way. So when the TV/Chromecast appear on the network, we know to switch on the power socket.

energeniesockets

Here’s the small Energenie transmitter attached to the GPIO headers on my B+.. it’s pretty tiny and the case I’ve got still fits over the top. Notice the small hole where you can attach an aerial.. if you want extra range, then you’ll need to solder one on.. I added a 135mm wire, since the range I got out of it just wasn’t enough to get from the dining room cupboard to the living room.

energeniepi

 

To put this together, we can use the Raspberry Pi Network Spy code I wrote in my previous blog posts on element14;

Raspberry Pi Network Spy – Part 1 – Initial Setup + d/b Schema
Raspberry Pi Network Spy – Part 2 – D/b Setup + PHP for the scanner

All we need is a new PHP page that’ll call one of the functions we’ve already written.. we need a list of the MAC addresses that are currently visible on the network, then check whether the Chromecast is there. Once we know whether the TV/Chromecast is on or off, we then call a Python script that will turn the Energenie socket on/off.

Here’s the PHP;

arp-chromecast.php

The Python script could follow the Energenie example script, but there’s actually an even more simple Python package which I’ve used in this project. To install it I did the following;

sudo apt-get install python-pip
sudo pip install energenie

Then I wrote this helper Python script (which we’ll call from PHP) that accepts a couple of parameters, like this callenergenie.py [on|off] [switch_number];

callenergenie.py

from energenie import switch_on, switch_off
import sys

if len(sys.argv)==1:
print ‘Please specify arguments like this callenergenie.py [on|off] [switch_number]’
print ‘eg. callenergenie.py on 1’
print ‘eg. callenergenie.py off 2′
else:
on_or_off = sys.argv[1]
which_switch = int(sys.argv[2])

if (on_or_off==’on’):
print ‘Switching on ‘, which_switch
switch_on(which_switch)

if (on_or_off==’off’):
print ‘Switching off ‘, which_switch
switch_off(which_switch)

Now that we’ve written the PHP & Python, all we need to do is run the PHP every minute to scan the network and do the switching. We’ll do this using another cron job;

crontab -e

*/1 * * * * sudo /usr/bin/php /var/www/arp-chromecast.php