Brian's Brain

This blog post references my hands-on feature article 'Homeland Security: Monitoring And Manipulating Remote Residences' in EDN's November 22, 2007 edition. It's one of a series of web addendums to the print writeup.

As I happily reported last week, my INSTEON-based home control setup seems to finally achieved a stasis of robustness, after I identified and subsequently avoided two misbehaving (for as-yet-still unknown reasons) power outlets. As such, I was highly motivated to proceed forward with the next step in my residence-tech plan; the ability to remotely adjust the thermostat trip point for my home's forced-air heating system, so that I could keep the inside temperature low (albeit still above freezing!) for both economic and environmental benefits while I'm away (or there, but asleep), but still return (and awaken) to comfortably warm surroundings.

Unfortunately, INSTEON-based thermostats are still in development (and will likely cost several hundred dollars when they're eventually available), and I'm reluctant to spend the money, time and effort to install an X10-based thermostat due to the archaic technology's "unacknowledged, ‘press-and-pray’ signaling" approach (link is to a PDF). Instead, last week, I dropped $8.99 on Ebay (plus $7.80 for shipping, handling, and insurance) on a model TH2807 thermostat set-back controller.

The 'X-10' mention in the product's documentation is deceptive; the TH2807 doesn't actually contain any home automation intelligence. It's a pretty simple design, befitting its low cost; a 20V (2W) AC-to-DC converter, a length of thin two-conductor wire, and the main module, which from my limited visual inspection (I didn't take it completely apart, because I don't want to break it!) predominantly consists of a four-position switch and two large (i.e. high-power) resistors.

I placed the TH2807 main module directly below my mercury-switch thermostat, with the DC converter controlled by a Smarthome model 2856S3B On/Off Appliance Module. The TH2807 main module has three 'on' settings (in addition to off):

• Low: approximate 5 degree Fahrenheit boost
• Medium: ~10°F
• High: ~15°F

With the TH2807 set on 'high', it draws (according to my Kill A Watt power consumption analysis unit) only 10 mA of current, alternatively stated as consuming 1VA and 1W of AC power (compare that against a home heating system set to an unnecessarily high temperature for an extended period of time!). When I turned the TH2807 on last night, the interior temperature was 68°F, but within five minutes the thermostat's sensed ambient temperature ramped up to 83°F.

Last night's outside temperature was unseasonably mild (translation: judging from the lack of frost when I woke up this morning, it didn't get below 32°F), so the interior temperature only dropped to 63°F. The TH2807-warmed thermostat read 78°F until I shut the set-back controller off via the INSTEON appliance module...within 10 minutes, the thermostat-sensed temperature had dipped below 70°F and the heater kicked on.

Don't get me wrong; I still plan to test-drive dedicated home automation thermostats, which among other things will give me more precise interior temperature control. But for now, the TH2807 accomplishes the vast majority of my desired objectives...and my wallet's also happy!