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Soil Moisture Hygrometer Sensor Module for Arduino Automatic Watering Systems
Soil Moisture Hygrometer Sensor Module for Arduino Automatic Watering Systems
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Soil Moisture Hygrometer Sensor Module — Analog & Digital Output, Arduino Automatic Watering
A resistive soil moisture sensor module that measures the volumetric water content of soil by detecting the electrical resistance between two probe electrodes. Outputs both an analog voltage (proportional to soil moisture level) and a digital threshold signal (HIGH/LOW based on a user-adjustable comparator). Compatible with Arduino, ESP32, ESP8266, Raspberry Pi, and any 3.3V–5V microcontroller. Ideal for automatic plant watering systems, smart garden monitoring, greenhouse automation, and agricultural IoT sensor nodes.
Technical Specifications
| Parameter | Value |
|---|---|
| Operating Voltage | 3.3V – 5V DC |
| Output Type | Analog (AO) + Digital (DO, threshold-based) |
| Analog Output Range | 0V (wet) – VCC (dry) — inversely proportional to moisture |
| Digital Output | LOW = soil wet (above threshold) / HIGH = soil dry |
| Threshold Adjustment | Onboard potentiometer (LM393 comparator) |
| Comparator IC | LM393 dual differential comparator |
| Probe Material | Nickel-plated steel (corrosion-resistant) |
| Power Indicator | Red LED (power on) |
| Threshold Indicator | Green LED (digital output active) |
| Operating Temperature | 10°C – 60°C |
| Connector | 4-pin 2.54mm header (VCC, GND, AO, DO) |
Pin Reference
| Pin | Label | Description |
|---|---|---|
| 1 | VCC | Power supply 3.3V–5V |
| 2 | GND | Ground |
| 3 | DO | Digital output (HIGH = dry, LOW = wet) |
| 4 | AO | Analog output (0–VCC, inversely proportional to moisture) |
Typical Applications
- Automatic Plant Watering: Connect DO to Arduino digital input; trigger a relay or water pump when DO goes HIGH (soil dry). Adjust the threshold potentiometer for the desired moisture level.
- Smart Garden Monitoring: Read AO via Arduino ADC for continuous soil moisture percentage display on an OLED or LCD screen
- Greenhouse Automation: Multi-sensor soil moisture monitoring across greenhouse beds with ESP32 WiFi reporting to MQTT broker or Home Assistant
- Agricultural IoT Nodes: LoRa or NB-IoT connected soil moisture sensor nodes for precision irrigation in field crops
- Indoor Plant Monitor: Capacitive soil moisture alert system for houseplants with LED or buzzer notification when soil is too dry
- STEM Education: Introductory sensor project for Arduino and Raspberry Pi beginners learning analog/digital sensor interfacing
Arduino Wiring & Code Example
- VCC → Arduino 5V | GND → Arduino GND
- AO → Arduino A0 (analog read) | DO → Arduino D7 (digital read)
- Read analog:
int moisture = analogRead(A0);— higher value = drier soil - Read digital:
if (digitalRead(7) == HIGH) { // soil is dry, activate pump } - Adjust the blue potentiometer on the module to set the dry/wet threshold for the DO output
FAQ
Q: Why does the analog output decrease when soil is wetter?
A: The sensor measures resistance between the probes. Wet soil has lower resistance, which pulls the analog output voltage lower. Dry soil has higher resistance, resulting in a higher analog output voltage. This is an inverse relationship.
Q: How long do the probes last in soil?
A: Nickel-plated probes are more corrosion-resistant than bare copper, but prolonged exposure to moist soil will cause oxidation over time. For long-term deployment, consider a capacitive soil moisture sensor (no exposed metal electrodes) for better durability.
Q: Is this compatible with 3.3V microcontrollers (ESP32, STM32)?
A: Yes. The module operates at 3.3V–5V. Connect VCC to 3.3V and the AO output will range 0–3.3V, compatible with ESP32 and STM32 ADC inputs (max 3.3V).
Package Contents
- 1 × Soil moisture hygrometer sensor module (controller board + probe)
