Description
The 12V Humidity Switch Relay Module (Blue) is an intelligent environmental control device designed to automate equipment based on ambient humidity levels. Operating on a stable 12V DC input, this module features a high-precision humidity sensor and a built-in relay that acts as an automatic switch. When the surrounding humidity reaches your preset threshold, the relay activates or deactivates connected devices such as exhaust fans, dehumidifiers, mist makers, or pumps.
The module includes a clear blue LED display and tactile push buttons for easy configuration. With its ability to switch between humidification and dehumidification modes, this single module solves both over-humidity and under-humidity problems. Housed in a compact, industrial-style casing, it is suitable for DIY projects, greenhouse automation, HVAC systems, industrial drying cabinets, and smart home integrations—all without needing a programmable logic controller (PLC) or microcontroller.
Key Features
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Dual Operating Modes – Switchable between Humidification (turn on when dry) and Dehumidification (turn on when wet) mode.
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Built-in 12V Relay – Capable of controlling high-power devices (e.g., fans, pumps, solenoid valves) directly.
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Adjustable Hysteresis – Prevents relay chattering by allowing a user-set switching differential.
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Real-Time Humidity Display – Blue backlit digital screen shows current humidity percentage.
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Simple Calibration – One-button sensor calibration for accurate readings.
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Non-Volatile Memory – Saves your settings permanently, even after power loss.
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Wide Application – Works for home grow tents, reptile terrariums, cigar humidors, printing workshops, and server rooms.
Technical Parameters
Usage Guide
Wiring Instructions
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Power Input (12V DC) : Connect the positive (VCC) and negative (GND) wires from a 12V power supply to the two-pin terminal block marked 12V / GND.
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Load Connection:
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Common (COM) : Connect to one side of your AC/DC power line.
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Normally Open (NO) : Connect to your device’s live/hot wire. Relay closes when humidity setpoint is reached.
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Normally Closed (NC) : Connect to your device’s live/hot wire. Relay opens when humidity setpoint is reached.
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Sensor : The external humidity probe (included) must be placed in the target environment, away from direct heat or water splashes.
Configuration Steps
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Power on – The display shows current humidity.
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Press SET – The “H” (high limit) value blinks. Use UP/DOWN to adjust the trigger humidity.
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Press SET again – The “L” (low limit / hysteresis) value blinks. Adjust the switching difference (e.g., 5% means relay resets 5% away from setpoint).
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Press SET a third time – Select mode:
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Wait 5 seconds – Display returns to normal; settings saved.
Example for Dehumidifier: Set H=70%, L=5%, mode=C. Relay turns on at 70% RH, off at 65% RH.
Q: Does this module work with 5V or 24V systems?
No. This version requires a regulated 12V DC power supply. Using 5V will not trigger the relay; 24V will damage the module.
Q: Can I directly connect a 220V AC fan?
Yes. The relay is rated for 10A at 250V AC. Connect the fan’s live wire through the COM and NO terminals. Ensure proper insulation.
Q: Why does my reading show "---" or "LL"?
This means the humidity is below 10% or the sensor is disconnected. Check the probe connection; the sensor must be plugged into the 3-pin header firmly.
Q: What is the difference between H mode and C mode?
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H (Humidify) : Relay ON when humidity is lower than setpoint (e.g., to turn on a mist maker).
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C (Dehumidify) : Relay ON when humidity is higher than setpoint (e.g., to turn on a dehumidifier)
Q: Can I use this for both home and business?
Absolutely. Home users control grow tents, wine cellars, or bathrooms. Businesses use it for warehouse dehumidification, egg incubators, or greenhouse fogging systems.
Q: How often does the sensor update?
The module samples humidity approximately every 2 seconds. The relay will not switch faster than once per 5 seconds to protect connected appliances.
Q: My relay clicks on and off rapidly. How to fix?
Increase the L (hysteresis) value. For example, change from 3% to 8%. This creates a larger deadband between ON and OFF points.
Q: Does the module remember settings after a power outage?
Yes. All programmed values (setpoint, hysteresis, mode) are stored in non-volatile EEPROM memory.
Q: Is the humidity sensor replaceable?
Yes. The module uses a standard resistive humidity sensor (HR202 or equivalent). You can purchase a replacement 3-pin probe from electronics suppliers.
Q: Can I test the relay without changing humidity?
Yes. Press and hold the UP button for 5 seconds in normal display mode to manually toggle the relay ON/OFF (test mode). Restart power to exit test mode.
