Designing Embedded Hardware

Understanding Schematics

You won’t get very far in electronics unless you know how to draw and read schematics. They crop up everywhere, and understanding them is a must. The schematics are like an architect’s blueprint. They show what components will be used in a circuit and how they are connected together. The schematics may also include other information such as construction directives. A schematic may have a list of revisions indicating what changes have been made to the original design. These are commonly called Engineering Change Orders, or ECOs for short. As a design grows and changes over time, it’s a good idea to keep track of what changes were made and, just as important, why they were made. Just as commenting source code is important, so is keeping track of the ECOs.

You will come across two types of schematics. You will see schematics in datasheets, books like this one, and other technical documents. These schematics will just show the circuit (or partial circuit), maybe a note or two, and that’s all. The other sort of schematic is the actual drawing(s) used to generate a circuit board. These schematics represent a full system design and will often have a title block located in the lower right of the sheet, indicating what the sheet represents, as well as who drew it and when. Figure 2-39 shows an example title block.

Figure 2-39. Title block

Essentially there are two ...