Wednesday, April 20, 2011

Expanding the System even more

The lessons I've learned about XBees and ethernet on an Arduino started coming together.  My latest project is expanding the monitoring around the house.  I followed up on my own ideas and put my Mega 2560 in an enclosure with it's ethernet card and an Xbee running in API mode.  I sample the two thermostats and average their temperature reading giving me the inside temperature.  Then I mounted an XBee to the side of a wall wart and hooked a temperature sensor to the side of it and plugged the new device into an outlet outside.  I now have outside temperature available.

That means I absolutely HAVE to upload it to Pachube doesn't it?  I put code in the new box to support a web server and client for Pachube and now I have all the readings from before regarding power but also record the outside temperature as well.  One funny thing is that the LM34 temperature sensor combined with the 1.2 volt maximum on the XBee means I have a maximum temperature of 120F that I can record.  Well....this is Arizona and it gets over that pretty regularly in the summer so I used a voltage divider to double the range up to 240F.  Let's hope that's enough (global warming and all).

I'm going to create a new page for the new black box I'm calling the House Controller and put the wall wart temperature sensor on the XBee page.  Those little XBees are not the cheapest radios in the world, but the temperature sensor is wireless and still has three analog ports I can use for around $28.  If I was to use one of the cheaper radios and arduino with the supporting hardware, I'd be pushing at least $40.  At some point in the future I'm going to have these little radios all over the house

The pachube page is :  House Monitor  The House Controller is: House Controller

And, for you hackers out there, it checks to be sure you're coming from an inside address and have the secret word before it'll let you change anything.  It isn't perfect protection, but the worst one can do is change the temperature on the thermostat during off-peak hours.  It's an arduino, not a big ol' web server.

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