AITRIP 10 Pack Capacitive Soil Moisture Sensor Corrosion Resistant for Arduino Moisture Detection Garden Watering DIY Electronic for Arduino and Raspberry Pi (10PCS)

These carry the proper timer chip (TL555C) to cover the 3-5V range per the timer chip spec rather than the NE555 which will work, but is technically not rated to function at 3V. They also include the voltage regulator which can sometimes be missing. All ten produced a very similar response running off a 3V pin on a Feather MO with some minor variation: ~760 dry to ~290 wet. As a check, I purchased additional sensors from two other vendors and these were the best in build quality and sensor response range. All came individually wrapped with individual cables. So far, so good- am purchasing a second set from this vendor and returning the others purchased from the other two vendors.

All ten sensors I received had the 555-timer chip reversed, which obviously made them unusable. Instead of returning them, I de-soldered the chip and placed it in the right position and the sensor now works.If you see the no 1 pin (indent) facing the connector, the chip is reversed (pic 1), no 1 pin should be next to R2 (pic 2).

The batch that I got didn't have any problems. This type of sensor can be hit or miss, but it worked without having to repair anything

The circuit has a fault and a 1 meg ohm resister needs to be installed for it to function properly. With the modification it works reliably with good measurement repeatability.

First of all mine are connected to a NodeMCU and they work with VCC of 3.3 and 5V just fine. (Esp considering they have an onboard 3V regulator.) These didn't have any issues with response times either, it was almost instantaneous. They don't have much of a range approximately 1V wet and 2V dry, but it's enough. The board appears to have a conformal coating, but I doubt the connector can withstand being watered. I covered the entire electronic section with Duct Tape to ward off any damage from accidental spillage.

Issue 1: The schematic in the listing is not accurate - part IDs are wrong, there are not 8 caps on the board, etc. I traced the schematic, attached. I did not measure the capacitors, and assume they track the posted schematic. Also, my pin numbers on the VR are incorrect (I grabbed the wrong VR model).Issue 2: These are set up to have almost a digital response, which may be fine for some applications. With R1 = 10k Ohms, AOUT is at about full scale (fully saturated, 1V) when the sensor is only dipped into water to about the "i" in "Moisture", which is less than 10mm. I needed a useful reading across the full range of moisture, so I changed R1 from 10k Ohms to 1k Ohms. See the attached graph.Theory of operation - the 555 timer is set up as a free running / astable / multi-vibrator oscillator. Assuming C3 is 470pF (per the schematic posted on Amazon) then the frequency should be ~870 Hz. The duty cycle should be roughly 50%. The output is fed thru R1 to the sensor capacitor, creating a AC voltage on the sensor capacitor that varies based on the moisture on the sensor - the higher the moisture (higher capacitance) the lower the amplitude of the 870 Hz on the sensor capacitor. This waveform is then rectified and filtered and sent to AOUT (there is a good amount of ripple on AOUT). AOUT swings between ~3V when dry to ~1V when fully wet.Making the sensor fully immersible - I 3D printed a cable guide / strain relief (search for model 488741 at Printables dot com) and gooped the electronics and cable connection up with Liquid Electrical Tape (search Amazon).

First of all they won't work at all if you are using a bi-directional level switcher, you must plug it directly into the pi at 3.3v.it won't work with 5v at all.You must add a 1Mohm resistor between Analog and Ground or else it takes 40+ seconds to adjust the reading to the current value.These are trash, do not buy. I bought the Gikfun version of these and they work as expected with a bi-directional level switcher and readings are nearly instant.

Cheap reliable moisture sensors. The electronics parts are obviously not meant to be put directly in the water so make yourself a nice case or use something like liquid electric tape.