Interfacing to External Devices

Explore Digital Interfaces techniques Introduce some complex optical devices and how to interface them Describe methods for switching devices on and off

Interfacing Digital Input Signals

General requirements of all digital input signals: The voltage input level should only be the

legal allowed voltage. They should not be corrupted by glitches They should switch cleanly and fast.

Forms of Signal Degradation

Simple Interfacing for Digital Signals

Switch Debouncing Switch debouncing happens when

mechanical contacts switch and thus from the force of the switching they bounce for a few milliseconds.

Actual switch Bounce Signal

Hardware Methods for Debouncing

Software method of Debouncing 1

Software method of Debouncing 2

Interfacing Keypads 1

Interfacing Keypads 2

Keypad Scanning Algorithm

Optical Devices: Single 7-segment Display

Optical Devices: Multiplexed 7-segment Display

Optical Devices: Example Circuit

Optical Devices: Opto-Isolator

Object Sensors

Shaft Encoders

Angular Speed S = output frequency / number of holesrevolutions per second

This setup does not give indication of direction

Incremental Quadrature Shaft Encoder

Absolute Shaft Encoders

Inductive Load Switching

Examples of Inductive Loads

Mechanical Relays

The use of H-Bridge 1

The use of H-Bridge 2

The use of H-Bridge 3

The use of H-Bridge 4

Semiconductor H-Bridge 1

Semiconductor H-Bridge 2

http://www.dprg.org/tutorials/1998-04a/