I've made a start on a microcontroller based controller for dew heaters. Based on an Ardunio Duemilanovo and an SHT15 Temp/Humidity sensor. Fiddling with some code off the web I can measure Temp and humidity and calculate the dew point.
I'm also planning on using some Dallas 18B20 1-wire temperature sensors to measure the tube temp at the heaters. I've not yet tried out the 1-wire stuff but there is plenty of material on the web to support that.
http://datasheets.maxim-ic.com/en/ds/DS18B20.pdf
I've not decided on how to control the heaters yet, an idea I've considered is for each heater unit to have 3 * 1-wire devices and a power switch device associeted with it. If I could get that to work I'd put one each of 1-wire eeprom, switch and temperature sensor at each heater. The eeprom would hold the addresses of the switch and temp sensor. The Arduino could search and find all the eeproms connected to the 1-wire bus and get the info it needs from them to know which temp sensor and switch were associated with each other.
The weakness in that is that I've not worked out how to take advantage of PWM to control the rate of heating. The strength is that I could have a number of heater unit's to plug into a common bus as suited the occasion.
I've still got to work out some aspects of the heaters, I found a supplier on ebay selling bulk rolls of nichrome wire and have made a start on one. I got some thermal transfer tape from Jaycar and wrapped it around some aluminium tube then wound nichrome wire onto that. I've covered that in some insulation sheet I have as leftovers from building a furnace. Some mechanical issues still bug me about that so I may revisit the whole thing.
I've attached a photo of the Ardunio, the SHT15 and an 18B20. I've also attached a screenshot of the software to control the Ardunio, in real use the Ardunio would run stand alone. I've attached the code I'm using at the moment as well for those who want an idea what's involved.
Bob