Designing Embedded Hardware

Chapter 4. Building It

No thing happens in vain, but everything for a reason and by necessity.

—Leucippus, On Mind

Before we get into designing a machine, let’s spend some time looking at how to produce the physical machine. Building a computer that doesn’t work is really easy. You may have a perfect design and flawless code, but ignore the physical environment in which the machine exists, and you’ll have built yourself a very intricate paperweight.

In this chapter, I’ll also show you how to lay out a circuit board (and where to be especially careful) and how to debug your hardware. In particular, I’ll examine how to physically produce the design for the ATtiny15 computer, which is presented in Chapter 6. I assume that you’re hand building in small quantities, so I’ll target the discussion accordingly. What I present here is not the state of the art in circuit board design or assembly, but guidelines for cottage-industry computer production. If you need to make production runs of hundreds of thousands, either you already know what you’re doing (and can skip this section) or you need to talk to a professional.

Avoid Noise

Digital systems are inherently analog in operation. Digital signals suffer degradation and noise due to analog effects present in the system. Spurious noise or reflections from nearby electrical machinery or radio transmissions can induce signals within your circuit that can cause false events to occur or even prevent a digital system from functioning at all. ...