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I'm building a traditional Italian pizza oven in the back garden and would like to get some temperature data back to my home computer. The major requirements for such a piece of kit are:

  1. Record a temperature of at least 500c
  2. Have reliable data recorders - once their set in concrete they're not coming out
  3. Send data back to my house (which is out of wifi range)
  4. Operate on battery power (edit: I'm happy to have a on/off switch but would like data every 5-30s when on and using the oven)
  5. Operate in the UK climate, so be operable from around 0-30c, I can keep the box with the electronics under the oven so will be out of extreme cold/heat

I'm a programmer by trade so more than capable coding and building electronics. I'm aware of the existence of Arduino but are also aware there are many other possible solutions.

My initial thoughts are a thermocouple with some kind of radio wave back to the house but that's pretty much where my limit of electronics gets me. Can anybody give any pointers on typical setups that would fulfil these criteria?

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I agree that thermocouples sound like the best sensors.

Take a look at some of the delta-sigma converters. In one recent design I was able to read thermocouples without any amplification. That's useful since the input offset voltage of a amp can be significant compared to a thermocouple's output voltage. I did add a FET to each input to effectively short it together so that the software could do auto-zero. You will also need a regular temperature sensor on the board because thermocouples only give you relative temperature, not absolute. You need absolute on your board to compute the absolute temperature in the oven. This may sound more complicated than it is.

I would be careful about casting things in concrete. Metal has a way of deteriorating, particularly at high temperature. I think it would be a good idea to allow for replacing the thermocouples and their leads. Maybe you can cast a small conduit in concrete instead of the wires directly. That way you can change the wires thru the conduit while the conduit (just a small pipe) stays in place.

As for getting the data back to the house, it would be useful to know how far that really is. Since this is a one-off and apparently all on your own property, I wouldn't get too worried about your local RF regulations. You can use a fixed directional antenna at both the oven and the house to get longer distance. WiFi sucks a lot of power and will give you much higher data rate than you need, although it would be convenient to connect to on the house side. The oven can be a TCP server that the computer in the house checks in with.

802.15 radios sound more appropriate, although again we need to know the distance. As I said before, two directional antennas would greatly increase distance and chance of anyone else noticing your signal. The Microchip MiWi protocol sounds like it would be a good choice for this. The data rate is low, but that's fine for this application. The nice part is that it's low power and you can shut down the oven side completely between transmissions, with the house side always on because it has much more power available. The drawback is that you then need a MiWi to ethernet bridge, but that's not all that hard.

We're actually working on distributed MiWi modules with a wall-powered base station that reports the collected data over ethernet via a custom TCP server. We've got things mostly working, but haven't released the code or the units yet. The code will be available for free when we do.

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  • \$\begingroup\$ An alternative for the communication can be XBee. Extremely simple to use: just connect to UART (protocol is completely transparent). Line-of-sight range for XBee: 90m, XBee-PRO: 1.6km. Or is your garden bigger than that? :-) \$\endgroup\$ – stevenvh Jul 10 '11 at 16:30
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I know someone who did almost exactly what you describe, minus the wireless link. He, too, set thermocouples into the structure of the oven while it was being built. Word of advice, though - you should test your thermocouples before you embed them. Of the 8 or so my friend was intending to use, one tested bad.

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A thermocouple, signal conditioning and an XBee or arduino with bluetooth would probably be simplest.

However, rather than embedding the thermocouple, I'd embed a stainless steel tube that the thermocouple could be inserted into. That way, you can replace them as needed.

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