SparkFun Forums

[InfernusDoleo]

So I have a whole-home humidifier. When the furnace is on, water showers over a filter in the furnace and it humidifies the air. The problem is that as long as the relative humidity is below the target point, the water is on. Constantly. Theres NO need for the water to be on that much.

So I'd like to build something that can sense moisture on the filter, and when it gets dry, a relay turns the water on. When its wet, it turns off.

My question is where to get a moisture sensor like that? I've seen plans for a soil moisture sensor, but the problem here is I need something that can sense surface moisture - it wont be submerged in anything. I guess I can try soldering 2 wires close together and sensing the resistance when it's wet... havent tried it yet. Wanted to ask here first.

Also would like to do this with components and NOT an arduino - would like to avoid that extra cost, but, if figuring all that out is too hard, I'll arduino it.

But, first, how to do a water sensor...

[AndyC_772]

Try googling "capacitive polymer humidity sensor".

[Mee_n_Mac]

Might it be good enough (and simple) just to time pulses of water when the humidistat calls for moisture ? Use a typical day to set the duty cycle and pulsewidth to a better balance. If you wanted to be tricky I suppose you could adjust the duty cycle according to the difference between sensed moisture and the desired moisture level/setting but at that point you might as well build your sensor and make it closed loop.

[InfernusDoleo]

I dont need to sense humidity - theres already a humidistat controlling if the water is on.

The problem is, as long as the humidity level is low enough to have the water on, the water is ON, and it POURS through the filter, wasting gallons of it every heating cycle. I want the humidistat already in the mix, but only turn the water on when the filter is dry...

Sure I could do it with a timer, but thats less accurate. And for something like this, sure, thats probably good enough, but part of it is playing with it and learning something new.

[esklar81]

It seems to me that what you need to change is flow rate, not timing. How about restricting water flow. If you were to do that by putting a misting nozzle at the current water discharge point, you could probably improve your humidification speed and drive your water waste to nearly zero.

Eric

[lyndon]

Are you sure there isn't a valve somewhere to adjust the flow rate? I had an Aprilaire unit in my furnace on a previous house and it wasted very little water. The waste went into a 3-gallon bucket that was pumped out every few days when it filled up. Never paid any attention to it but I'm sure it just used a trickle of water.

[InfernusDoleo]

Nope. No valve. It DOES have a pinhole valve that was used to attach it to the waterline, but it's either off, or on too much. Its not a fine control.