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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →The Mk22 is an Arduino soil-moisture indicator built around the Crowtail Moisture Sensor 2.0. It reads the sensor on analog input A0, compares the reading with a project-set threshold of 300, and shows “Dry Soil” or “Humid Soil” on a Crowtail I2C LCD, with yellow and green LEDs as indicators. The threshold is an example setting for this build—not a calibrated moisture percentage or a universal watering rule.
How the Mk22 moisture indicator works
The project describes the sensor as using two probes in the soil. Current passes between them, and the sensor infers moisture from electrical resistance: wetter soil conducts more readily and has lower resistance, while drier soil conducts less readily and has higher resistance. This is the principle described by the project page; it does not establish independent accuracy or durability testing for the Crowtail Moisture Sensor 2.0. DFRobot Maker Community’s Mk22 project listing identifies the build and its implementation.
The code calls analogRead(A0) and applies this decision:
- A reading greater than 300 is labeled “Humid Soil.”
- A reading of 300 or less is labeled “Dry Soil.”
The project comments describe a rough range of 0–700, with 0–300 treated as dry and 300–700 as humid. Those are code comments and choices for this build, not standardized sensor specifications. The loop refreshes the reading once per second.
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#1 Best Overall
- Soil moisture level and status at a glance; shuts down irrigation when desired moisture level has been reached
- One-touch override allows soil moisture bypass for special conditions
- Includes moisture sensor probe and electronic module
- Use with X-Core, Pro-C and I-Core, and ACC Clik sensor inputs
- Warranty period: 5 years
Parts and pin connections
The project listing names these components:
- Crowduino Uno SD
- Crowtail Base Shield
- Crowtail Moisture Sensor 2.0
- Crowtail I2C LCD
- Crowtail green LED and yellow LED
- USB battery pack
- USB Mini-B cable
The listed controller connections are:
| Component or signal | Connection |
|---|---|
| Moisture sensor signal | A0 |
| Crowtail I2C LCD | A4 and A5 |
| Yellow LED | Pin 7 |
| Green LED | Pin 6 |
| Power | VIN to +5 V |
| Ground | GND |
These are the Mk22 project’s listed connections. If you substitute a board, display, or cable, check that the board has an available analog input, the connectors are compatible, and the power requirements match. The project page does not supply a complete manufacturer datasheet for the exact Crowtail sensor.
Setting a useful threshold for your setup
Treat 300 as a starting point for reproducing the example, not a watering prescription. The project does not document a calibration procedure or establish that a particular reading corresponds to a given soil-water content or plant need.
Rank #2
- Zigbee Hub Required: Compatible with standard Zigbee 3.0, such as Echo (4th Gen), Echo Plus (1st Gen and 2nd Gen), Echo Studio, Eero 6, Eero Pro 6, Home Assistant (ZHA & Z2M), Hubitat and SmartThings Aeotec, Homey, Homey Bridge, Homey Pro. A Zigbee hub is required. Gen2 is optimized for stronger and more stable wireless performance, helping ensure consistent data transmission
- Stable Monitoring, Smart Irrigation: Designed to deliver more consistent soil moisture readings, helping reduce data fluctuations and improve confidence when deciding when to water your plants. It widely adapts to various soil environments, guaranteeing your plants always receive the right amount of water
- Capacitive Monitoring: Unlike traditional probes, capacitive sensors are less affected by soil salinity and pH, offering greater durability and a longer lifespan in various soil types. Suitable for various gardening places including farms, greenhouses, nurseries, gardens, and potted plants
- Enhanced Antenna for Stable Coverage: Featuring a reinforced antenna design for more stable signals, this sensor dramatically extends your signal range. Even when the sensor is placed in the living room, on the balcony, or in a garden corner, it maintains a reliable connection with your Zigbee gateway. This ensures stable data transmission in complex home environments, making indoor smart gardening more worry-free
- Remote Monitoring and Automation: Receive real-time alerts on your smartphone, allowing you to take action anytime, anywhere, ensuring your plants get the right care. Integrated with smart home systems, these sensors enable automated watering schedules, so you can manage and control your garden's irrigation remotely, saving both time and effort
- Upload or adapt the Mk22 code while retaining its A0 sensor input and the rest of your board’s correct pin assignments.
- Observe readings in the soil and conditions where you intend to use the indicator. The example labels values at or below 300 dry and values above 300 humid.
- If you choose a different threshold, change the comparison in the code to match your own observations. The project listing does not specify a universal calibration method.
Soil type, sensor placement, and the exact hardware setup can affect how useful a reading is in practice. Use the indicator as a project-specific signal rather than interpreting its labels as calibrated percentages.
Keep Crowtail specifications separate from Grove specifications
Seeed Studio documents a separate Grove Moisture Sensor with an operating voltage of 3.3–5 V and example readings of 0–300 for dry soil, 300–700 for humid soil, and 700–950 in water. These are Grove product figures, not Crowtail Moisture Sensor 2.0 specifications. Seeed Studio’s Grove Moisture Sensor documentation demonstrates an analog-input approach for that product. Its Grove sensor support FAQ explains that its analog reading represents output voltage converted by the Arduino ADC, and says higher output voltage indicates more moisture for that Grove module. Neither source confirms the Crowtail sensor’s voltage range, output range, or electrical behavior.
Rank #3
- 【Reliable Wireless Soil Moisture Sensor】: Equipped with advanced chip, ECOWITT WH51 wireless soil moisture sensor collect soil moisture data within 72 seconds when totally inserted into the soil. The data can be transmitted via GW1000/GW1100 Wi-Fi gateway( sold separately ) and the live data can be viewed on WS View Plus or Ecowitt APP after Wi-Fi configuration done.
- 【Support Pairing with Various Ecowitt Gateway/Consoles】: The GW1100 Gateway(sold separately) supports up to 8 WH51 Soil Moisture Sensors, and the channel name can be edited. When paired with a Weather Station Console (HP2551/HP3500/HP3501), up to 8 channels WH51 sensors supported and you can view soil moisture data in real-time on the Display. When paired with Console WH0291, you only can view soil moisture data in real-time on the Display.
- 【Uploading to Ecowitt Weather Server】: Supports uploading to our free Ecowitt weather server(ecowitt.net) to view the soil moisture data graph and download the history records on the website; support setting and receiving email alerts from the server; channel names can be edited on the website; supports remote monitoring with smart phone, laptop, or computer by visiting the website.
- 【Indoor & Outdoor Use】: The IP66 waterproof moisture sensor can be used for indoor & outdoor potted plants, lawn, garden, farm etc. ★ Please Note : ecowitt WH51 soil moisture sensor is designed to measure soil moisture ONLY. Do not touch the stone or hard rock soil. ★
- 【NOTE BEFORE PURCHASE】: Ecowitt WH51 soil moisture sensor could not directly display the soil humidity readout, which can not be used alone. North America:915MHz; Europe:868MHz; Other areas: 433MHz
What the project establishes—and what it does not
The Mk22 listing, attributed to Luc.Paquin and dated January 11, 2025, establishes the named sensor model, the A0 analog-read implementation, the example threshold, the described sensing principle, and the listed components. It does not establish the Crowtail sensor’s exact operating-voltage range, standardized output range, accuracy, calibration procedure, corrosion resistance, or expected service life. The project is therefore useful as a documented indicator build, but its threshold and “dry” or “humid” labels should not be mistaken for validated measurements.
Quick Recap
Best Value
- Capacitive Soil Moisture Sensor： Compatible with for Arduino Raspberry Pi
- Size：98*23mm
- Operating Voltage：3.3V DC；Output Voltage:0-3.0V DC
- Interface Type：PH2.54 3Pin
- Commodities include：10Pcs Soil Moisture Sensor；10Pcs connecting wire
Rank #4
- Country Of Origin: United States
- Model Number: 200SS-5
- Item Package Dimensions: 5.0" L x 5.0" W x 5.0" H
- Item Package Weight: 2.0 lb
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
