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I've been having some issues with my refrigerator lately, and so I've been imagining some kind of temperature logging system.

I want it to log the temperature every 5(?) seconds, door open/close events, and compressor start/stop.

Having little to no electronics experience, my head said the following:

  • Arduino-ish controller (or .NET CF, since I know C# best)
  • Amp-clamp thing around the power cable to register the compressor on/off (and some way to connect it to the Arduino
  • Photoresistor(?) to register the light on/off (for registering door open/close)
  • Some kind of temperature sensor of course (maybe multiple sensors for several zones in the fridge. Possibly with 2 decimal points of accuracy?)

The best would be to log to a web server using some kind of wireless networking (WiFi-shield?), but logging to an SD card could also be a possibility.

What kind of hardware would you recommend for this? And could it be a good "noob"-project?

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Adafruit has some related tutorials and kits you might find useful. The Arduino datalogger shield tutorial for monitoring light and temperature in your fridge seems right up your alley. It's logging with an SD card, but depending on how close your fridge is to your other computer(s), you might be able to use an XBee to transmit data. Another fridge data-logging project is here.

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You head seems to have the right idea generally :-).
You have provided a good enough answer in your question :-).
Anything much more becomes a shopping list without more specific technical questions.

  • Processor / Computer: - your choice - anything that works will work. Arduino or whtever is fine.

  • Temperature sensor ICs are commonly available.

    The famed LM335 is not the cheapest but is well known - about $1.70/1 Digikey.

    Many more listed at Digikey and elsewhere. Ad22103, AD592, LM61, ...

  • For extra points use a thermistor for temperature measurement.

  • For even more points use a silicon diode.

Compressor run could be sensed by noting sudden sharp drop in coil temeperature and cessation of same at end of run. Not as precise as direct monitor.

You should be able to sense compressor run by using a Hall effect sensor on the mains wiring or near the motor. Motor is often sealed in a metal can so maybe mains lead detection best. NB no mains connection needed !!!

Door open could be microswitch or internal lamp sensor or room light sensor. (Or PIR person sensor or RADAR or ... :-) ).

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Getting a WiFi signal out of your fridge (unless the case is all or mostly plastic) will be a challenge; you're probably better off planning to write an SD card.

If you don't compress your data, you'll need to store 2 bytes per sample or 1440 bytes/hour (3600[sec/hr] / 5[sec/sample] * 2[B/sample]. Depending on your choice of u-controller and your logging time requirements, this will fill up a small RAM rather quickly. You can either "borrow" some unused space in the program memory (flash) or you'll need to add on some storage.

(And yes, I think it will be a fine newbie project - I'm planning to do the same thing myself!)

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I would recommend Mastech MAS345 multimeter (it comes with the thermocouple) and a laptop computer. Connect the multimeter to the computer with a serial cable, and write a script to take measurements.

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Wicked Device makes an inexpensive product called the Wicked Node that you could put in your fridge with an LM34 temperature sensor (or similar) mounted and set it to 10-second mode. Then set up an Arduino with the Wicked Receiver shield plugged into it and you could log the data to your computer. It should work up to a few hundred feet away from your fridge...

If you also set up a magnetic reed switch or some kind of push-button in your fridge on sensor input 4, the Wicked Node will also be used to count the number of times that switch was "pressed" (i.e. the door was opened) during each interval and send that as part of the data it transmits every 10 seconds...

If you were so inclined, each Node could host up to three temperature or LDR sensors as well to get your "zone" concept. Many Nodes can transmit to a single Receiver, although in 10 second mode, you'll probably have trouble with more than three or so.

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