Greenhouse irrigation


Use a range node to scale it up.




150 seconds ? I'm sorry :pleading_face: I just don't understand what the output of the PID node refers to



It's the number of seconds that the pump would be activated for.
...or should I say the number of seconds that should elapse before switching the pump off.

More seconds = more water!

So if your PID outputted 1, that would be scaled up to 150, which in turn would activate the water pump for 150 seconds.



Is the scaling based on you personal choice, based on your experience or on a reference ? Thanks in a advance



Trial & error!! it depends upon what rate you are delivering water, the type of soil etc.
I started with minimal water delivery and gradually increased until I was happy that the PID could gain control, and maintain the moisture level that I wanted.

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All right, Thank you very much!!



In fact my suggestion is to use node-red-contrib-pid as you originally suggested. If you feed the output of the PID into that then it will generate an on/off time proportioned signal (effectively a very slow PWM) which you can use to control the water valve. So if for example the pid asks for 25% (actually 0.25) then it will switch the relay on for 25% of the time and off for 75% of the time, with the cycle time as set in the timeprop node. So if the max flow rate is set to that which is required in the worst case then it should do the job. Alternatively if you think you will never want the valve on for more than, say, 10% of the time you can use a Range node to convert the pid 0:1 to the range 0:0.1 and feed that into the timeprop node.

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That makes a lot of sense, thank you !



more expensive but perhaps better acurate : sht sensor for soil humidity

What do you think about it ?



I'm not that familiar with those devices, but a quick google search suggests that they aren't intended for long term exposure to submersion/high humidity conditions.
It appears to be a SHTx sensor mounted in a fine metal mesh, intended to allow air to blow through, but fine enough to prevent short term water ingress.