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  • Author Author: PEarle
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PiFace Home Timeswitch - turning a light on and off

** Update**

 

I've now implemented this using an Energie Pi Controlled mains Socket - see my blog at Home Automation using ENERGENIE - ENER002-2PI

 

For details on the Energie socket see ENER002-2PI - ENERGENIE - RF CONTROLLED MAINS SOCKETS, FOR | CPC

 

 

One of the things I wanted to do with my Pi from the outset was to be able to use it as a timer, to turn a light on and off at night when I was out, as a simple form of home security. Being something of a newbie when it comes to electronics, my biggest problem was how to wire it up to be able to turn the power on and off.

 

The Pi relays are rated at a maximum of 20v and 5amps - therefore I cannot connect the Pi directly to the 'mains powered' light !!!

 

What I am planning on doing is investigating using a to a commercial relay which can cope with the current. When I've done that I shall update this blog again with details of the how the Pi can safely control a mains powered device.

 

However, the rest of the blog is still valid as it explains how the relay on the PiFace is operated and will be used for the Timer application, when completed.

 

I've written a java program to control the light switching on and off which does the following;

 

  • Calculate a random wait time between two values that I have supplied (2 and 20 minutes at the moment)
  • Wait for that period of time to elapse
  • At the end of the wait time, toggle the relay - switch it on if it was already off, and vice-versa.
  • repeat the above ad infinitum

 

The result is that the light will keep turning on and off in a random pattern making it look as if someone is using the room even when I'm not there !

 

 

Java Code

I've already written a document about using Java on the Pi - see http://www.element14.com/community/docs/DOC-54112/l/java-on-the-raspberry-pi. The code that I used for this project is attached to this document (e.g. timeswitch.zip)

 

 

Running Automatically

My intention is really to have this as a 'black box' function so that the TimeSwitch application will run as soon as the Pi is switched on. This is accomplished quite easily - all I need to do is write a script to run the java application, and then add it to the initialisation script.

 

The script to run the java application is as follows ;

cd /opt/pi4j/examples
java -classpath .:classes:/opt/pi4j/lib/'*' com.phe.datetime.TimeSwitch

To run at start up I have edited  /tec/rc.local and added the following line

 

/opt/pi4j/examples/timeswitch.sh > /opt/pi4j/examples/timeswitch.log

 

This will execute the java app at start up and also pipe any log messages to timeswitch.log.

Attachments:
timeswitch.zip
Parents

  • I'm adding to Mark's warning  - this is a totally unsafe use of UK mains power and this blog should be taken down immediately. It should be obvious to Farnell/Elememt14 that a great many complete novices are interested in RPi applications and know no better than to copy whay they see. If they copy this some oneis likely to be seriously injured or killed.

     

    MK

  • in reply to michaelkellett

    Thanks Michael - Ive changed the blog and removed the phot of the PiFace connection that I made.

  • in reply to PEarle

    Peter

    It was me who started the comment ...

    Your post is still inaccurate.

    Luckily, the PiFace comes with a couple of relays built in which can switch mains (204v) voltage up to 10 amps, which is more than enough for my needs.

     

    Rather than include any words regarding 230v, I suggest you use this.

     

    "The Piface is designed for switching no more than 20v and 5A, so I will connect it to a sperate relay to switch the mains voltage for my application."

     

    People read what they want, and this removes the opportunity for them to read the WRONG voltage.

     

    I have done a home minder using Arduino, and you could very easily use small desk lamp that uses a 12v lamp to achieve the same result.

    Its surprising how the room appears illuminated when its shone onto a wall, or similar light coloured surface.

     

    Thanks

    Mark

     

    PS apparently I can edit it the document ... not sure thats quite right.

     

     

    edit 04/09/13 rectified the issue.

  • in reply to mcb1

    Peter

     

    One thing I mentioned in the article for "Home Minder" I did was to ensure the device couldn't fall or shift while you were away.

    As we found in Christchurch with the earthquakes, some things tended to move, and arriving home to find the charred remains of your house is not the best coming home present.

     

    So electrical safety isn't the only consideration when you leave appliances on while away.

     

    Mark

  • in reply to mcb1

    Hi Mark - thanks for your comments, and also your advice above, which I will be incorporating into the project. The points about making sure the device is contained within an appropriately robust container are very useful.

     

    Ive been away on vacation for a week, without Wifi acccess - I just had time to make a quick edit before I left. I've now changed the content to remove any mention of 240 volts!!

     

    Once again, thanks for your help.

     

    Regards,

    Peter

  • in reply to PEarle

    Much better Peter.

    I've edited the comments.

     

    Just one thought about random lights.

     

    If you were standing outside looking at a house you think might be unoccupied.....

    Would a light randomly switching ON and OFF at 2am, 3am, or even 4am not seem a little wierd.?

     

    The idea is to emulate occupancy, so a quick note of any 'normal' behaviour might be in order.

    Adding some time ranges to the random along with a set number of cycles within that period could be an advantage.

    Adding a sequence to simulate kitchen then bathroom might be also a bonus.

    If you could incorporate a RTC, then simulating normal weekday activity could be a benefit, ie lounge off at 10pm, bedroom off 10:30pm, etc.

     

    Please don't get me wrong, this has potential, and is not dis-similar to an Arduino based version I did earlier.

     

     

    mark

  • in reply to PEarle

    Peter,

     

    The points about making sure the device is contained within an appropriately robust container are very useful.

     

    There seems to be somewhat of a conflict between the need for a robust container,

    and the Safety Data Sheet's warning that the device should not be covered.

    http://www.element14.com/community/docs/DOC-44828/l/raspberry-pi-safety-data-sheet

     

     

    One of the things I wanted to do with my Pi from the outset was to be able to use it as a timer, to turn a light on and off at night when I was out, as a simple form of home security.

     

    The Safety Data Sheet also warns that the device is not Class B compliant, which seems

    to be in conflict with its proposed use as a simple form of home security.

  • in reply to mcb1

    Mark this raises my point made to E14 that their should be a mark on such a project to raise caution for any one reading it or that Certain project can "vote" a project "dangerous" or "safety critical" so that readers can use their common sense and realise what they are doing can be dangerous. Mind you if you need to be told it's dangerous then the project probably isnt for you any way !

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  • in reply to mcb1

    Mark this raises my point made to E14 that their should be a mark on such a project to raise caution for any one reading it or that Certain project can "vote" a project "dangerous" or "safety critical" so that readers can use their common sense and realise what they are doing can be dangerous. Mind you if you need to be told it's dangerous then the project probably isnt for you any way !

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