Digital Inputs
A digital input typically consists of a power supply (voltage source), a switch and a voltage-sensing device (analog-to-digital converter). Depending on the switch’s open/closed status, the sensing device detects a voltage or no voltage condition, which in turn generates a logical 0 or 1, on or off, alarm or normal or similarly defined state.

Circuit Diagrams
The following circuit diagrams are examples of commonly used digital input configurations.

Continue on to Chapter 1: Digital Outputs