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The HCV Webserver is run on a Raspberry pi - 2 watts power, $40 complete!
Our freezers now have their own Twitter account! How's that for weird?
Click here for the world's most boring twitter feed!
The graphs update about once an hour, hit refresh to see up to date readings.
All temperatures are measured with Wireless things...
When the monitor is started it shows a flat line, as time passes this line is slowly filled from the right with real readings.
If you're sad enough you can track people opening and closing the doors during the week, then the long quiet period over the weekend as the monitors sit undisturbed.
Replace the lithium batteries when the reading above goes below 2V. Using 2 x AAA batteries we got ~9 months (19th July 2012 - 29th March 2013). We swopped to 2 x AA batteries and got a year and a half (30th March 2013 - 15th Sept 2014, 5th floor -80°C freezer above).
This wireless system cost < £80 to build (including the computer!) and works for any temperature down to -80°C. For further details click here.
As you can see, we've now extended this to monitor lots of freezers (and other things), For further details click here.