HVAC monitoring using opto-isolators?

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm working on a home environmental/energy monitoring system. I would like to monitor our 2 HVAC systems so I know when they are on, how long and what mode (heat or cool). My plan is to use mostly 1-wire network for data gathering. So that the HVAC I figure it would be best to monitor the “Heat” or “Cool” control leads via opto-isolators. Then feed that into a 1-wire GPIO device. So my question is what opto-isolator would I use for this? I know about using them with a Triac to turn on 120v AV, but I need to monitor 24 AV instead. Any suggestions?

-Chris

2

you could also use a single one wire temp sensor in the unit: temp drop cool on, temp raise = heat on - added benfit is that you know your unit's not only on but that it's working correctly...