Arduino relays are typically controlled with low voltages, either 3.3V or 5V.
Here's a more detailed breakdown:
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Control Voltage: The voltage needed to activate the relay's coil, causing the switch to change states. This is usually the voltage supplied by the Arduino board's digital pins. Common values are 3.3V (for some boards like ESP32) and 5V (for Arduino Uno and similar boards).
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Load Voltage: This is completely independent of the control voltage. The load voltage is the voltage the relay switches on or off. Relays are designed to switch a wide range of AC or DC voltages depending on their specific ratings. This could be anything from low voltage DC (e.g., 12V) to mains AC voltage (e.g., 120V or 240V). Do not confuse the relay control voltage with the voltage it is switching!
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Arduino Compatibility: Because Arduinos typically operate at 5V, most readily available relay modules are designed to be controlled with 5V. However, 3.3V relay modules are also available and are used with boards like the ESP32 and ESP8266.
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Important Consideration: When selecting a relay module, ensure its control voltage is compatible with your Arduino's operating voltage. Also, carefully check the relay's maximum voltage and current ratings for the load you intend to switch. Exceeding these ratings can cause the relay to fail and could be a fire hazard.
For example, you can control a relay using the 5V output from an Arduino Uno to switch a 120V AC appliance. The 5V from the Arduino controls the relay, and the relay safely switches the 120V AC.
