Interfacing AC power lines with PIC microcontrollers
Applications like automatic power factor correction, power measurement, and power line monitor require interfacing the high voltage AC power lines to microcontrollers. This application note from Microchip describes a simple method for measuring parameters from the AC power line by using only one external resistor, and is more reliable than using a bulky and expensive transformer. This method takes advantage of the input static protection circuitry that exists on I/O pins of a CMOS PIC16C5X. These protection circuits are designed to short the inputs to the power supplies when a large overvoltage is applied, thus protecting the chip from static electricity spikes.
Input static protection circuitry on PIC I/O pin