I switched to pre-made I/O boards, which makes everything 100 times easier and I can change things whenever I like. I would have definitely liked to discover these sooner!
I am having a lot of problems with the fact that when the moisture sensor is in the soil, the plant seems to have power through it. I realised when the tip of a leaf touched my face, and I felt a bothersome sting. I powered the unit off, and the sting disappeared. The plant is showing sign of stress when it shouldn't.
The probe is inserted horizontally in the pot, touching the soil. The problem occurs even if only half the probe is in the soil. The pots are in plastic pots on ground made of cement. The sensor's circuit is not touching water or soil in any way (as I said, the problem is there even if the sensor is half in). The room seems to have substantial EMI. I am not sure if it's relevant, but there is soil all around the room, which is... well, "well grounded".
I measured the voltage. It changes quickly; my multimetre is not fast enough, but it goes from 300mV to 1500mV.
Where is the tingling sensation coming from? Why is the sensor somehow powering the plant? Any hints on how to discover more and debug this further?
Try coating the edges of the soil moisture PCB with varnish/shellac/nail polish. Sometime water can migrate under the coatings and make contact with a PCB trace
It wasn't -- not properly. I noticed huge fluctuations every 10 seconds in the sensor's reading. I shortened the cable and used a very shielded cable, and the fluctuations went away.
Well yes, it was at roots height.
Oh wow OK. I had the same problem with a brand new sensor just after inserting it in...
Would it be that quick?
The sensor doesn't use much power; should I use a MOSFET to power it instead?
Do you think the "power through the plant" problem might be due to the sensor being powered by the pin...?!?
Just to be 10000% clear. you are recommending using nail polish on the EDGES of the the sensor, all around it, right?
I am just amazed that they would sell something that need users to do that (!).
Having the board in close contact with the roots.
No, wait. The board (the non-sensing part of the thing) is completely OUTSIDE of the pot. In fact, some of the sensing portion is also outside of the pot, just to be sure. The only part IN the pot (and touching roots/soil) is the sensing parts, placed horizontally
Improper power.
Won't the sensor degrade more quickly that way?
I'm not sure how well those capacitive sensors work if they are horizontal
It's not actually horizontal, it's on a 45 degrees angle, and yes they do work fine for my use.
(But, you do need to put a "sock" on the sensor to make it actually work properly...)
Multimeter is on the board's ground and... in the water.
The sensor is partially immersed in water (not all of it).
It's powered with the Arduini D3.
At the beginning, the reading was very low. We weren't quite sure we could feel it when using a wire in the water then touching our faces, shoes off.
I then added a small amount of salt (as in normal salt) in the cup. The reading went through the roof. When my wife placed the testing cable in her face, she screamed. Not painful, just unexpected, and very stingy. I can assure you it's NOT pleasant. This is similar to what I felt when dealing with the plants (which have salt-based fertilisers).
Is the power supply connected to your AC mains? Are you certain nothing bleeding through?
Set your voltmeter to mains voltage AC.
Connect your voltmeter negative lead to a known ground.
Connect the positive lead to your board ground.
Get a reading? Dial the setting down to ensure you are not getting AC power from the mains.
Just a thought.
Wait, what you are saying is that I might be seeing NOT the current that the sensor is leaking, but the voltage drop between the circut's earth and the main's earth?
