I've been slowly getting the automation hardware and code moving along, and I've got the home made Temperature sensor up and running now.Originally I was going to use a simple Thermistor and do the conversions on the Netduino, but it wasn't working very well, plus it was going to need a lot of extra code that the .NET Micro Framework didn't have. Namely a Pow function and a Log function. Of course, there's lots of those available, but I didn't want to go adding more code to an environment that only has 64kb of space
So I ended up going with the good ole LM35DZ instead. There are literally hundreds of tutorials for this IC and it provides a straight centigrade value as an analog voltage. Super easy to read on an Analog pin in the Netduino.
The trick was going to be putting everything together in a way that would stand up to extended submersion in salt water.
Enter the Bic Pen! Hollow plastic with enough space to run the sensor through and no exposed metal (once the parts are removed of course). Run the line through, fill with silicone, and we've got a temperature sensor for roughly 45 cents.