Reed switch is a kind of passive electronic switching component with contacts with a simple structure, small size, and easy to control. It consists of a sealed glass envelope where there are two ferrous elastic reeds and is filled with an inert gas called rhodium. Normally, the two reeds are separated in the envelope. When a magnetic substance approaches the glass envelope, the reeds will come together due to the magnetic field thus completing an electric circuit. When the external magnetic field disappears, two reeds will be separated because of their elasticity, the circuit is also disconnected. Therefore, as a circuit switching device controlled by magnetic field signals, the reed switch can also be used as a sensor for counting and limiting, etc. (Applied in the security systems, mainly used for the production of door and window magnets), and it is also widely used in a variety of communications devices. In practice, it is common to use the two permanent magnets to control the connection of two metal sheets, thus it is also called a "magnetron".
The reed switch must work together with the magnet, when it detects magnetism, the circuit is connected and the module outputs a low level; when there is no magnetic force, it is disconnected and the module outputs a high level. If the sensing range of the reed to the magnet is more than 1.5cm, it will become insensitive and it may not be triggered;
DO output terminal on the module can be directly connected to I / O port of MCU, the trigger state of the reed switch can be detected through MCU;
DO output terminal on the module can be connected to the IN terminal on the relay to form a high-power reed switch for direct control of high voltage.