A relay is an electrically operated switch. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages.
2-channel 5V relay
2-Channel 5V Relay Module is a relay interface board, it can be controlled directly by a wide range of microcontrollers such as Arduino, AVR, PIC, ARM and so on. It uses a low level triggered control signal (3.3-5VDC) to control the relay. Triggering the relay operates the normally open or normally closed contacts.
4-channel 24V Relay
This is a 4-Channel DC 24V Relay Module High/Low Level Triggering Optocoupler Isolation. Using high-power relay, the maximum control load DC 30V 30A / AC 250V 30A. ... Each channel has a relay on LED indication.
4-channel 5V Relay
The 4 Channel Relay Module is a convenient board which can be used to control high voltage, high current load such as motor, solenoid valves, lamps and AC load. It is designed to interface with microcontroller such as Arduino, PIC and etc. It also comes with a LED to indicate the status of relay.
Triggering the relay operates the normally open or normally closed contacts. It is frequently used in an automatic control circuit. To put it simply, it is an automatic switch to control a high-current circuit with a low-current signal. 5V relay signal input voltage range, 0-5V. VCC power to the system.
Four-way 5V relay expansion board
5V 4 Channel Relay Module 4-Channel Relay Control Board for Arduino with Optocoupler Relay Output 4 Way Relay Module 4CH.
Relay Shield v1
he Relay Shield provides a solution for controlling high current devices that cannot be controlled by Arduino's Digital I/O pins due to current and voltage limits.