Designing Embedded Hardware

Routing a Design

So, with all that in mind, let’s create a simple circuit board for an AVR computer. This design is covered in detail in Chapter 6, but for the moment, we’ll just use it as an example so that we can see the process of producing a printed-circuit board.

We start with the schematic (Figure 4-13). This design brings together the voltage regulator circuit, the AVR processor with a status LED, and the in-circuit programming interface.

Figure 4-13. The full schematic, including connector for I/O and programming

Note that no connection is made for pin 2 of the connector. This is the +5V supply provided by the programmer. Since our embedded system has its own supply of +5V (VCC), the external source is not required. (If we were building a 3V version of this computer, then we would need to use the programmer’s +5V supply, and we’d have to disable the output from the voltage regulator during programming.)

From this design, we use our schematic editor to generate a netlist file, which tells the PCB editing software what interconnections need to be made.

Importing the netlist file into the PCB editor automatically loads the component footprints. These are manually rearranged to provide optimum placement, ensuring shortest track runs between components (Figure 4-14). Note how related components—such as the voltage regulator, C1, C2, and the power connector—are placed together. ...