This book developed out of a need for an in-depth work about the Raspberry Pi that just didn’t seem to exist. If I had found one, I would have gladly purchased it. A quick survey revealed a large number of “how to get started” books.
But I pined for something with the kind of meat that appeals to engineering types. Give me numbers, formulas, and design procedures.
Almost all of that information is available out there on the Internet somewhere. But I discovered that some questions take considerable time to research. If you know exactly where to look, the answer is right there. But if you’re just starting out with the Raspberry Pi, you have several online Easter-egg hunts ahead of you. How much is your time worth?
Here’s a short sample of some of the questions answered in this book:

• How much current can a general purpose input/output (GPIO) port source or sink?
  
• What is the resistance of the GPIO internal pull-up/pull-down resistor?
  
• Which GPIO does the 1-Wire interface use?
  
• What is the GPIO voltage range for a 0 bit or 1 bit?
  
• How do you budget the GPIO power?
  

Some of these questions have simple answers, while others require an “it depends” explanation. You might be wondering why you need to know the internal GPIO pull-up resistance. Chapter 27 discusses this in connection with motor driver interfaces and what happens at boot time. A number of questions arise when you start designing interfaces to the outside world. While you may not aspire to be an electronics engineer, it helps to think like one.