'MySensoring' an HVAC Fresh Air Intake System.

[RJ_Make]

Here is another completed project using MySensors. My current HVAC system is controlled by a Honeywell YTHX9421R5085WW/U Prestige IAQ control system which works great and has a boat load of options, but has one problem for me. The web access system does not allow control of the fresh air system remotely. It can only be control by the thermostat directly. So I decided that with MySensors I should be able to change that.

With this "mod" I'm able to remotely:

1. Activate the fresh air intake system (open a motorized damper, turn on the fresh air blower and the HVAC blower)
2. Detect when the thermostat is sending a fresh air signal. (This allows me to turn on exhaust blowers on the upper floor)
3. Lock out the thermostat from turning on the fresh air system. (used when humidity is too high)
4. Physically active the fresh air system.
5. Monitor the fresh air intake air temp (mixed air temp)

The project is very similar to my EH40 project, with a few exceptions.

1. Utilized the HVAC's 27vac to power the project.
2. Used mb6s surface mount rectifiers. (had them laying around)
3. Used a Optocoupler. (I had a lot of fun messing around with that)(Used it for the detection circuit)
4. Used a DC to DC converter to lower the 27vdc down to 5vdc

Here are some pictures of the work..

Thermostat fresh air signal detection board:

Case with relays and slot cut out:

Others:

Well until next time...