Relay control refers to the use of electromechanical or solid-state relays to control electrical circuits by opening and closing contacts in response to an external signal—usually from a microcontroller, PLC, or smart device.

What is a Relay?
A relay is an electrically operated switch. It uses a small control signal to activate an internal switch, allowing or stopping the flow of a much larger current.

Electromechanical Relay (EMR) – Uses physical movement of contacts.

Solid-State Relay (SSR) – Uses semiconductor components, faster and silent.

Key Features of Relay Control Systems
Remote Switching
Relays can be controlled via Wi-Fi, LoRa, Zigbee, RS485, or direct microcontroller signals.

Electrical Isolation
Protects control circuits from high-voltage or noisy loads.
High-Power Switching
Can handle AC or DC loads like motors, lights, fans, or pumps.

Smart Integration
Easily integrated into IoT, BMS, HVAC, and home automation systems.

Common Relay Control Applications
Home Automation
– Control lighting, fans, heaters, appliances remotely.

Industrial Automation
– Motor control, pump systems, warning systems.

Greenhouses & Agriculture
– Automate irrigation pumps, ventilation systems, or grow lights.

HVAC Systems
– Relay-based control for AC compressors, dampers, and air purifiers.

Relay Control Methods

Control Type                         Description                                     Example Use Case
Manual                 Physical switch activates relay                    Local light switch
Timer-based         Relay operates on a schedule                     Smart watering system
Sensor-triggered    Relay responds to sensors (temp, CO₂)    Ventilation control in HVAC
Remote/App          Wireless command via app/web                 Smart home device control

How It Works – Example (Smart Relay Control)
Sensor detects condition (e.g., CO₂ > 1000 ppm)

Microcontroller or IAQ monitor sends signal to relay

Relay activates exhaust fan or alarm

System logs data or alerts user via mobile app