Need to Track HVAC Operation on My PC

Outstanding! Multiple I/O's, USB, software, cables, and only $25. I can track our utility power (they ignore me about brownouts and blackouts) and other stuff. Thanks for reply. Is CR4 great or what?

In past experiments, I've "triggered" data capture at a slow rate (0.1-10 Hz) based on voltage threshold settings. This created a new data file each time a trigger condition was satisfied. The file-names were automatically created & incremented. Each event file had date and time of creation. Event rates and Sample rates were low, so file size and number of files were never excessive.

LINE VOLTAGE ISOLATION IS CRITICAL FOR SAFETY!

For generic line voltage monitoring, I would use a small AC transformer, bridge rectifier, filter cap, and one or two resistors.

Suggest:

120/240 Vac primary, 6.3 Vac secondary, 200mA, transformer
(4) 1N4001 diodes (almost any diodes or a prepackaged bridge should work fine)
47 uF , 15 V , capacitor
1 kΩ pot or equivalent (390 Ω and 470 Ω)

see crude sketch below for basic concept...



Good luck SSCpal

Yes, thanks for the drawings. Dare I comment, that's a lot of work in place of the "AC-input" modules that I mentioned (they have the ac-bridge-driven rectifier-opto stage and a 15ms time constant with Schmitt trigger all included)?

BTW, as a "design and build rather than buy" type of guy, ready to hook up to the AC line, you might prefer buying a raw ac-opto element, e.g., an LTV-8141, SFH6286 or PC364N, for about 50 cents, and taking it from there. :-)

This is almost spooky; I sketched this circuit in bed last night:

..and the optoisolators are a great idea, too. Where would this world be without engineers? Thanks, guys.

> old Ben and Jerry column I read as a kid in Popular Electronics

Awwe, sheesh! Of course that was Carl and Jerry, not Ben and Jerry!

No need to connect to the compressor power directly.Use the 24 volts from the thermostat wiring(green wire) to determine on or off state of compressor.You can use a relay to isolate this from the input of the data logger, and run the + from the logger thru the contacts of the isolation relay.An optoisolater circuit can be used instead, if you are electronically inclined.

HTRN

I don't know if this will help, but the LabView way of doing things (search on it) seems to be oriented toward interfacing with a PC. There probably are I/O devices (contact closure, 4-20 ma loop signals, etc.) that can transmit on computer-friendly protocols such as USB and Ethernet. I have done bit-banging stuff like this in the past, but not recently, and thus I am out of date on some options that might work best for you.

May I remind the present generation that we used to "read" the inputs on individual pins of parallel connectors on a standard PC - for output, very simple basic program statements can write words to a parallel port. A simple programs parses the input word periodically, can create graph or data file by following one or more pins. Cheap for relay logic setups. Parallel port cards are still available. =>Enginer<=

I had a similar problem on Windover Way in Titusville FL. My mother inlaw (blind) lives there and has complained loudly about tripping breakers and odd sounds and poor performance from her AC especially if she is using her oven. I pulled the face of the panel and checked tightmess on the AC connectors and all was well. Her nieghbors has issues too. I called the power company and offered to pay to have the transformer checked. They sent out a man the next day. They spent the next few days working on transformers in the area. It seems a corrosion problem at the tramsformer was to blame. The power company was courteous, quick, smart about the approach and, very effective. No more problems after that.

I am buying some of the stuff that has been cited here to track other things at my house. These people have given you excellent advice.