DDC Online direct digital controls
Guide to DDC

Chapter 1:Input Output (IO) Basics

Digital Outputs

A digital output typically consists of a switch (either mechanical as in a relay, or electronic as in a transistor or triac) that either opens or closes the circuit between two terminals depending on the binary state of the output.

Circuit Diagrams

The following circuit diagrams are examples of commonly used digital output configurations.

Figure 2 shows an open collector transistor-type digital output operating a pilot relay, which in turn energizes the motor starter coil for a fan. Figure 3 shows a triac-type digital output operating a pilot relay that is used to energize a fan motor starter coil.

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