A relay is an electrical switch used to open or close a circuit. The circuit is opened or closed by a small current signal, which may be generated by a sensor or some other component. In other words, the relay allows a small current to control a larger current. Relays can also be used to convert a single current signal into multiple signals, or to convert a single signal into multiple current signals. There are two types of relays - mechanical relays and solid-state relays. Mechanical relays use electromagnets to open or close circuits. When the relay coil is energized, the electromagnetic field produced by the current in the coil attracts the relay's movable contacts, thus connecting the switch contacts. Solid state relays are devices that use semiconductor devices to open or close circuits. The main difference between solid state relays and mechanical relays is that solid state relays don't have any moving parts. Solid state relays are smaller, lighter and quieter than mechanical relays. They also have faster response times, higher operating speeds, and higher reliability. Solid state relays are also more compact than mechanical relays, so they take up less space in an electrical circuit. 5V Relay Module, a module that can be easily integrated into a project. It has the ability to switch on or off a high power relay using a small 5V input signal. The module can be used to control a wide range of devices and appliances, including lighting, motors, and heating/cooling systems. It is also useful for projects that require high current switching. This module comes with a built-in optocoupler to isolate the input and output, making it ideal for projects that require additional isolation. The module also has an on/off LED to indicate when the relay is energized. The main advantage of 5V Relay Module is that it can be easily integrated into any project. It also has a high level of isolation, which makes it ideal for projects that require additional isolation. The module is also very easy to use and it does not require any complex wiring or programming. See more details about 5v relay module in AliExpress Video Page.