■ FIGURE 6. The schematic, all wired up.
■ FIGURE 8. The raw PCB layout.
70 September 2012
which is a PCB that plugs in on top of an Arduino. Next,
we move the parts. Notice that you can move the parts
anywhere, but that isn’t such a good idea when designing
a PCB. In fact, you want to move parts to specific
locations in relation to each other. Often, we have parts
that have pins that are on 0.1” centers, so let’s set up a
grid where parts can be moved around, and land on 0.1”
points in relation to each other. We see in Figure 11 that
we can check the “Align to Grid’ and ‘Show Grid’
selections in the View menu; we get the grid shown in
■ FIGURE 9. Moving parts to the board.
Now, let’s move these parts to reasonable positions
and add the wires. First thing you’ll notice is that every
time you try to grab a part, you end up grabbing the
Arduino! To prevent this, you right-click on the Arduino
part, select ‘Lock Part,’ then click ‘Raise or Lower.’ Select
the ‘Send to back’ option. Now you can move the other
parts that are sitting on top of the locked Arduino layer.
In Figure 13, I’ve moved the parts to the lower right
corner conveniently located to each other’s pins for
wiring. The lines connecting the pins are called the rats
nest (though I can’t imagine why) and they act like rubber
bands, indicating where the PCB wires are to go. Your
goal is to get the rats nest minimized so the wires can be
as short as possible. Next, note that the battery terminal
doesn’t have any indicator of which pin goes to GND and
which goes to the + 3 volt line of the battery, so I right-click on the VCC1 label for the part which gives me the
window shown in Figure 14. I then change the VCC1 to
‘GND + 3.’ I rotate the text and place it next to the
connector as shown in Figure 15.
Fritzing has an auto-router, but we won’t use it since
this is a very small board and I find routing is fairly
intuitive. You just click on a pin and move the wire to the
next connection and release it. Figure 16 shows what
happened when I wired the VCC, GND, and crystal pins.