Question 1

do you have a library for the arduino?  How do I calibrate these?  Getting an analog reading does not mean anything..

Accepted Answer

Take a reading while they are dry (that's your 0% reading), then take a sample of your soil and put it in a pot, insert the sensor and then water the pot until it can't hold any more water, then take another reading that's 100% saturated.
If you want you can put the sensor near a plant and see what level it reads when the plant looks stressed from to little water and make sure you keep it wetter than that.
Note: unless you are measuring pots, the moisture level near the surface is about useless for most plants unless they have very shallow roots..  for plants with deeper roots you probably want to waterproof the top portion of the sensor and bury it about 18" down.

Question 2

What is the max distance from a pi  using 3v3 and using cat5 cable can the sensor be and still work ok?

Accepted Answer

so not sure if you still need this answered or not, but for others it might help.
Im using an Arduino 5v, I used about 10 feet of cat5 cable from arduino to sensor. it changed the value some but you just need to calibrate it for that change.
example,
Arduino to senor without cat 5 = wet "850" / dry "450"
arduino to sensor with 10 feet cat 5 =  wet "700" /dry "300"

Question 3

how does this work? do i have to connected to something else?

Accepted Answer

Yes. Depends on what you want to do with it.
The output is a voltage value. You can connect to an Adruino type device to display it as analog or convert it to a calibrated digital display of percent moisture.

Question 4

Will this work (as is) with the Micro:bit?

Accepted Answer

I dont know understand your question. I plugged it into a data port on a esp 8266 read the data using C+ and  calibtrated it to meet my needs and transmitted it to a Blynk Control Panel  on the internet.

ASIN	B07SYBSHGX
Brand Name	SongHe
Country of Origin	USA
Customer Reviews	4.2 4.2 out of 5 stars (213)
Item Dimensions	9.8 x 2.3 x 1 Centimeters
Item Weight	90 Grams
Manufacturer	Songhe
Material Type	Ceramic, Metal
Maximum Supply Voltage	5.5 Volts (DC)
Measurement Accuracy	±15%
Model Number	F24
Mounting Type	Tabletop
Number of Items	5
Number of Packs	5
Output Type	Analog
Part Number	F24
Sensing Distance	98 Millimetres
Specific Uses For Product	Intelligent agriculture, Moisture detection, Garden plants
Style Name	Modern
UPC	738678030462
Upper Temperature Rating	55 Degrees Celsius

Capacitive Soil Moisture Sensor Corrosion Resistant for Arduino Moisture Detection Garden Watering DIY (Pack of 5PCS)

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