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One technique relay drivers from the microcontroller or computer can be made with the driver PNP transistors like the article "Interface Relays With PNP Transistor" ini.This circuit interface is simple and easily applied to a microcontroller or computer parallel port. Interface Relays With PNP Transistor uses 2 transistors 2N3904 and 2n2905/2N2907 UAH as a power relay drivers. The advantages of this circuit can menggeran relay with considerable power with TTL logic input from the computer and microcontroller. Source voltage required to follow the relay circuit is used, for example using a 12V relay, the source voltage to 12V or 24V relays the 24V voltage source. Detailed relay interface circuit and microcontroller or computer can be seen in the following figure.

Function diodes mounted parallel with the relay to prevent backflow into the transistor due to magnetic induction of the relay coil, therefore these diodes must be installed. For installation with a microcontroller or computer which need to be noticed is the Grund computer or microcontroller circuit must be connected to ground in series Interface Relays With this PNP transistors.