The Treehouse Blog

Doug‘s recent gift of some 1-wire temperature sensors set me on the path to some more in-depth home monitoring.  The extent of home monitoring to this point had been the use of two relatively ancient AP9605 ^(ad) boards for the SmartUPSes ^(ad) in my network closet and office.  This combination provides SNMP-able power load and temperature readings that I graph using NetMRG.

Another home improvement project I have recently completed is having a water softener/conditioner installed.  This system has a built-in water meter, which just begs to be monitored.  While reading about home monitoring projects in general, I had read that some power meters output IR pulses that count energy usage.  I used my digital camera after dark to confirm that my meter does indeed appear to do this.  Between these two items, I clearly had a use for two counters.  The other monitoring goal I had was temperature and humidity information for my crawlspace.  The bottom of the insulation in my crawlspace seems to get wet in the summer from condensation, and I’d like to keep tabs on it.

The core of this project involves having a 1-wire network.  For the PC interface, I elected to get a LinkUSBi from iButtonLink.  I opted for the “scratch and dent” model to save a few bucks, and I have not even noticed any real cosmetic issues with it.  I setup the OWFS software on my firewall by recompiling Doug’s SRPM for EL6.  I’m using a phone distribution block ^(ad) to connect the multiple 1-wire devices back to the LinkUSBi.  The one gotcha I’ve noticed with this is that the 1-wire interface requires the correct polarity and the majority of RJ11/RJ12 phone patch cables are rollovers – they swap pins.  When a 1-wire device is connected with reversed polarity to the network, the LED on the LinkUSBi stays lit constantly and no devices can communicate.

The crawlspace temperature/humidity sensor I selected was the MS-TH from iButtonLink.  At $64 it seemed overly expensive, but with pricing other options including kits, it still appears to be the best value for a 1-wire humidity sensor.  I installed it on the beam in the crawlspace and ran a new CAT5e run to it from the network closet, patched into the 1-wire bus.  I wrote a script to strip the leading spaces that OWFS provides (WHY?) and graphed the sensors in NetMRG.

In the upcoming part 2, I’ll discuss the details of the 1-wire counter setup to provide power and water metering.