@firetech, I agree, I use them for my computerized grow box, so simple to work with.

Naturally aspirated instead of turbocharged? Please.

janin-
It appears that the pdf is a writeup on the construction on a single aspirated thermometer and that multiple (10?) units were needed for multiple greenhouses. The T2SS boards were probably used to tie them all together at the control point. It’s a bit cryptic.

Actually, the write-up is just about the aspirated thermometer design, I haven’t gotten around to writing up the overall system. The T2SS boards mount in or on the unit heaters (depending on the type) to turn them on/off using the thermostat inputs. They are mostly 2 stage and around 220K BTUs/hr. All SSRs are OA5 type (http://www.embeddeddatasystems.com/1781-IO-Modules_c_52.html). The main boiler and circulator pumps are hooked up to an Opto-22 board hanging off the printer port of the controlling PC (runs FreeBSD). User interface is with a web browser.

> UR DOING IT RONG

Last night it dropped below 15 degrees Fahrenheit here. Glass has a U value (heat loss) of about 1.13. So enough glass to cover 22K+ ft^2 maintained at 62 degrees F inside needed about 1.7M BTUs/hr at that point. The heat shut off shortly after sunrise.

Thanks for giving feedback, Dave. As a side note, since you know electronics, why didn’t you also replace the expensive T2SS + OA5 by a simple DS2406 + a relay ? Maybe cost isn’t an issue to you, but you could save at least $50 per board.

if you also want to read humidity, add another thermometer that is kept wet (wet bulb thermometer). the temperature difference between a wet and dry thermometer gives relative humidity (and dew point). http://en.wikipedia.org/wiki/Wet-bulb_temperature

since this thermometer already has a fan, all one would need is a wick and a water container:
http://www.tifton.uga.edu/tobacco/wetbulb.htm
http://support.radioshack.com/support_tutorials/weather/weather-18.htm (also contains link to calculation table)

if both thermometers are in the same housing, the wet one should probably be after the dry one in the air flow.