This system is using battery 9Vdc and it will step down to 5V using LM7805 voltage regulator.
The voltage regulator module is used to protect PIC and other connected sensors or actuators from over voltage. This is because PIC and all other connected sensors, actuators all support 5V DC only. Over voltage will cause any of the module burn. LM7805 is used to regulate voltage in the system and output 5V DC (max current: 1000mA). It supports input voltage from 7V DC to 18V DC.
The output of each PIC pin is 5V with max output current of 20mA or 0V with 0mA output. The voltage is not enough to run high power device e.g. motor, solenoid. Thus we need a relay to control these high power items. A simple switching circuit (using NPN transistor, C9013) will be used to energize / de-energize the input coil of the relay.
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