The output of the relay, the output current and voltage are written on the outer casing of the relay, that is, the weak current is used to control the strong electricity. To what extent is the strong electric power, that is, the output parameters (such as 220V, 2A), the transistor output is different from the relay output. Although both are control devices, the input and output of the transistor are not electrically isolated, and the relay is electrically isolated. When the volume is limited, when the response time is short, transistor control is often used, and the voltage is relatively high. The current is relatively large. When paying attention to personal safety, the relay is often used. As for the relay as the input of the single-chip microcomputer, it is not necessary. The relay is an isolating switch. The weak current controls the strong electric power, and it seems that it will not receive the input pin unless You use a foreign signal to control the relay, and the relay pull-in state is input to the microcontroller. That is not necessary. The relay is just a switch with electrical isolation.
Relays are classified according to the number of their throws. The knives of the relay are the common terminals of the various paths. The position where the knife of each relay can be connected is the throw of the relay. A relay can consist of n knives and m throws. For example, a single pole single throw relay (SPST) has one knife and one throw.
The Type A relay is a single pole single throw type, and its default state is "Normally Open".
The Type B relay is a single pole single throw type, and its default state is "Normally Closed".
The C-type relay is a single-pole, double-throw type, which is first disconnected from one relay and then connected to the other (first broken and then connected).
A single relay is called a relay. The relay output is equivalent to a circuit that inserts a device such as a drive relay on a board and a few pins. For example, the DB-16R is a relay output board consisting of 16 C-type relays. A treasure brand human body sensor switch (ceiling C-type relay output), etc., as long as the input terminal receives the signal, the output terminal can drive the function of the alarm device, etc., that is, the infrared radiation alarm device has a relay inside, and is regarded as a relay through the relay. The output directly controls alarms or automatic door lights.