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[Working] Z-wave soil moisture sensor based on Fibaro RGBW module

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The Fibaro RGBW module and most LED controllers use Pulse Width Modulation PWM to adjust the duty cycle of power deliverd to the LEDs. Computer fan controllers use the same technology and its designed to wrok at 12V so I dont see why it wouldnt work as long as you stay within the max load ratings for each channel.

Try it and see, its all low voltage anyway, so pretty safe

OK, so couple of updates here:

Now it is almost a year of use and everything works fine.
The biggest problem are probes, which are becoming damaged fast.
I've tried capacitative sensor but it had very limited range presented between "dry" and "wet" (like only 25% of the 0-100% scale), finally got damaged by water (all electronics is on the same board as a probe, I thought that if it is above ground then nothing bad should happen, but I was wrong).
I've tried "anti corrosion probe" it worked well for quite long time, then unfortunately one pole went out as well.
Now I'm testing carbon sticks, which are working well. One pole gets some dirt on it which makes the probe stop working, but regular cleaning solves the problem. The probe itself doesn't wear off, at least I don't see visible changes yet.

I did some changes to the system and during the process accidentially connected RGBW with reversed polarity. Everything survived, fortunately, but since that RGBW shows humidity changes in very narrow range (like: 2% if dry and 5% if wet) I'm not sure if the issue is with RGBW or the arduino modules, I'll check it when I try to configure the second RGBW which I ordered. For now I changed the configuration of proper channels from "sensor" to "bistable switch with memory" and attached Arduino module in the way that it works as on/off switch (desired humidity is then set via potentiometer on the Arduino module).

I build a two zone system for watering plants on my balcony, based on the humidity sensor, pump put into a watertank and 12V water valves opening or closing accodrdingly to the zone which is watered. 2 valves and a pump took 3 channels so for now I have humidity sensor only for one zone, second is watered according to time schedule.
When I'll get next RGBW I will set probably second sensor as well as similar (but one zone only) system for plants in the living room. Next step is to integrate water level sensors (already installed in the tanks) which will send notifications when water need to be refilled. Unfortunately There would be not enough channels for that (2 zones + 2 humidity sensors + pump + water level sensor on the balcony + pump + humidity sensor + water level sensor  inside = 9 channels, while 2 RGBW's give me 8 ), so I will probably need to add binary switch to handle water level sensors, or I'll integrate sensor with pump in a way that the pumt will not run if water level is too low - then I would need to make a logic based on power consumption reported by the main device, or on the humidity (if it won't change after watering, then assume that the pump didn't run because of too low water level).

Does any Fibaro RGBW work or it has to be RGBW-441

Fibaro has only one RGBW device in their offer, which is RGBW-441

@kwieto thanks for all your observations. I'm ordering some sample Z-wave devices for yard control and your guidance is very useful to learn about new items to try out.

re: "One thing to remember - if input set to receive 0-10V signal it gives 100% when the circuit is open and 0% if it is closed. Don't be surprised that after you set specific channel like that, you'll see 100% (ON) reading when you didn't attached yet any device to it."
--> If this cause a problem, you could put a 10 to 100 kOhm resistor across the inputs to force the signal low when the circuit is open.

re: "I've tried capacitative sensor but it had very limited range presented between "dry" and "wet" (like only 25% of the 0-100% scale)"
--> For extended use outdoors, I think capacitive sensors are likely the way to go since they should not corrode nor be strongly dependent on salt concentration in the soil as the conductive sensors are. I ordered a couple from China to try. To scale up the voltage to 10V at saturated water conditions, a simple (single-chip and a couple resistors) linear amplifier can be made from an operational amplifier. The operational amplifier chip would draw essentially no current and could be powered from whatever voltage drives the Fibaro RGBW. When the parts arrive and I get this working I'll post a schematic.



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