Real World Instrumentation with Python

Interfaces

In an instrumentation system, the interfaces are where the software meets the real world. An interface might be as simple as an input to sense the open or closed state of a switch, the voltage from a temperature sensor, or pulses from a magnetic sensor on a rotating shaft. An interface can also be a data communications channel for interfacing with a self-contained instrument or controller of some type. It could even be another computer system, as in the case of an Ethernet interface.

Figure 2-25. Duty cycles

Discrete Digital I/O

A discrete digital interface gets it name from how the input and output bits, also called lines or pins, are organized, read, and controlled. Discrete digital I/O can be used whenever there is a need for sensing discrete input states or controlling something with discrete operational states. “Discrete” in this case means that each input or output line has a finite number of unique discontinuous states. With a discrete digital interface, this equates to two states: on or off, 1 or 0. Discrete I/O lines may be handled in software as either singular bit values or members of a set of bits. In some cases, a particular line may be configured as either an input or an output. In other cases, an interface may provide a set of lines dedicated to output, and another set for input. As for terminology, it is common to hear “discrete I/O” or “discrete line.” The ...