I am a rookie at this. (that seems to be a popular opening line)
I just got an arduino board and have figured out the leds and a couple other sensors and now I have a plan to put this to use. I have a wall controller for my Bryant HRV system. Long story short, during winter when it get really cold out here in Montana there is a humidity sensor that activates and brings in fresh, dry air from outside so the windows don't have puddles of condensation on them.
The problem is that the humidity sensor is a manual nylon thread that expands and contracts with the humidity and this trips the switch. It is very inaccurate, +- 8%. The switch is a separate component in the wall unit.
My vision is to disconnect the two wires that go to the switch unit and use an arduino and a digital humidity sensor to take the place of the switch.
Here is what I have found so far. The voltage across the two wires leading to the switch is 5V. The whole wall unit runs on 12VDC. If I short a wire across the two wires it will turn the system on. When tested with a ammeter across the two wires it draws .4 mA.
I went out on a limb and tried to use the basic "blink" code with the delay set to about 20 secs and connect grd and pin 13 to the two wires and could get the system to turn on and off every 20 seconds. Interestingly enough when the led went out the system came on. Maybe I had the wires backwards. This seemed encouraging.
Before I go any farther I figured I better check with the pros before I melt something and my wife rolls her eyes at me.
Questions: Can this work? Could I run the arduino off power coming into the wall unit? It has 4 wires coming into the box. I have the wiring diagram for the whole machine in hardcopy.
The ultimate goal would be to receive the temp from my 433MHz LaCrosse weather sensor and adjust the indoor humidity based on the outdoor temp. Like off of Practical Arduino.
Feel free to throw out any ideas.