Relay, also known as a relay, is an electronic control device that has a control system (also known as an input circuit) and a controlled system (also known as an output circuit). It is commonly used in automatic control circuits. It is actually an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays a role in automatic regulation, safety protection, conversion circuit, etc. in the circuit. Relay coils are represented in a circuit by a rectangular symbol. If the relay has two coils, draw two parallel rectangular boxes. At the same time, mark the text symbol "J" of the relay inside or beside the rectangular frame. There are two ways to represent the contacts of a relay: one is to draw them directly on the side of a rectangular frame, which is more intuitive.