87 lines
4.4 KiB
Markdown
87 lines
4.4 KiB
Markdown
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.. title: Automation: Has the oven warmed up yet?
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.. slug: automation-has-the-oven-warmed-up-yet
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.. date: 2010-06-07 14:55:54
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.. tags: Automation
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.. category:
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.. link:
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.. description:
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.. type: text
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-->
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In the Bang Goes the Theory episode [The Human Power Station] a family of four
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people had their electricity supplied by a large group of cyclists on cycles
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hooked up to generators, the point being to highlight the amount of energy that
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is used and wasted on a daily basis. There's a video on [youtube].
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One example that seemed to waste a lot of energy was cooking roast dinner. The
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oven was turned on to preheat (this is often the first instruction in a
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recipe), but it wasn't actually used until a significant time later, wasting a
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lot of energy. An example which may be more common is turning the oven on to
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preheat before cooking frozen food (which requires no preparation), then
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forgetting to check to see if it has preheated.
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This used to happen to me, but I've solved the problem by using my electricity
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monitor (I have an electric oven), mqtt and asterisk.
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First off, we need to monitor electricity usage. I do this with a [CurrentCost]
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CC128 (note that EON customers in the UK can apply to get one of these for free
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in an [Energy Fit] pack) hooked up to a low power computer that is running
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mosquitto. If you're running Linux, you can use [cc128_read.py] or
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[cc128_read.pl] to read the data coming from the monitor and publish it to an
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mqtt broker. A second client, [cc128_parse.pl], takes the data from the monitor
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and republishes it to the broker in a friendlier format - the Unix timestamp of
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the reading and the power usage, separated by a single space.
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To figure out when the oven has warmed up, I look at the electricity usage with
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the oven heater on - approximately 2.4kW. If the energy usage drops below this
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value, I know that the oven heater has turned off and so the oven has warmed
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up. This is of course slightly simplistic - I'm not actually measuring the
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oven, just the electricity usage so if I turned on the kettle at the same time
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it could cause my guess to be incorrect. When CurrentCost produce their
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individual appliance monitors, I'll be able to be certain of how much
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electricity just the oven is using.
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This uncertainty means that I only want to turn the oven monitor on when I've
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actually turned the oven on. Looking for an easy way to start the monitor, I
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spotted my house phone - a Siemens C460IP - which is a "normal" land line phone
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and an IP phone all in one. I've got Asterisk running on the same server as
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mosquitto, so it's an ideal solution for controlling things. Configuring
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Asterisk is way beyond the scope of this text, so I'm only going to talk about
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the bits I changed. I added a new extension number 100 which, when called,
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starts the oven monitor:
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```
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exten => 100,1,Answer()
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exten => 100,n,System(echo "/usr/local/bin/oven_pub.pl" | at now)
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exten => 100,n,Playback(oven-trigger)
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exten => 100,n,Hangup
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```
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This answers the call, starts the monitor, plays a sound clip so the person
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calling knows what has happened and then hangs up. I'm using the "at" command
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here as a simple way of putting the job into the background, thanks to [Ed] for
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the suggestion. The script [oven_monitor.pl] looks for the electricity usage to
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drop beneath 2kW, then runs `oven_warmed_up.sh` and exits.
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The final step is to do something in [oven_warmed_up.sh] to give feedback. I
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make use of asterisk once again and initiate a call to the phone - so when the
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oven has warmed up I get a phone call with a message that tells me so. The
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outgoing call is initiated by moving [oven.call] to
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/var/spool/asterisk/outgoing/, as shown in the script.
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Do you have any suggestions on how to improve this? Or other ways of using
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asterisk or mqtt like this? Let me know in the comments!
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[The Human Power Station]: http://www.bbc.co.uk/programmes/b00p8469
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[youtube]: http://www.youtube.com/watch?v=C93cL_zDVIM
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[CurrentCost]: http://www.currentcost.com/
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[Energy Fit]: http://www.eon-uk.com/media/energyfit.aspx
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[cc128_read.py]: http://bitbucket.org/oojah/mosquitto/src/tip/misc/currentcost/cc128_read.py
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[cc128_read.pl]: http://bitbucket.org/oojah/mosquitto/src/tip/misc/currentcost/cc128_read.pl
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[parse.pl]: http://bitbucket.org/oojah/mosquitto/src/tip/misc/currentcost/cc128_parse.pl
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[Ed]: http://twitter.com/ribzlike
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[oven_monitor.pl]: /files/examples/oven-asterisk/oven_monitor.pl
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[oven_warmed_up.sh]: /files/examples/oven-asterisk/oven_warmed_up.sh
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[oven.call]: /files/examples/oven-asterisk/oven.call
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