Electronics Cookbook

Chapter 15. Digital ICs

15.0 Introduction

In many projects the only digital IC you will need is a microcontroller. With sufficient GPIO pins you can do most digital tasks. In this chapter, you will find recipes for digital ICs that still manage to find a role in modern electronics design.

Sometimes, a single digital logic IC is all you need. A single digital logic IC is often cheaper and removes the need for programming that would otherwise arise if you used a microcontroller.

15.1 Protecting ICs from Electrical Noise

Problem

You want to use an IC, but you want to avoid errors caused by electrical noise.

Solution

Use a 100nF capacitor as close as possible to the power pins of the digital IC. The shorter the leads to the capacitor the better.

This process of connecting a capacitor with short circuit board tracks to the power pins of an IC is called “decoupling” because each IC has its own little reservoir of charge and will therefore not be “coupled” to a neighboring capacitor by affecting its power supply. Capacitors used in this way are also called “bypass” capacitors.

Figure 15-1 shows a circuit board containing a digital IC with a 100nF multilayer ceramic (MLC) capacitor for both a through-hole and SMD.

Figure 15-1. Decoupling Capacitors

The circuit board on the right of Figure 15-1 actually has two capacitors in parallel as the decoupling capacitor. The smaller one is ...