PCB BASICS
SCREENSHOT 3. Here’s a look at
the PIC18F2620 schematic
image before we identify it and
schematically wire it into the
design. Note the dots at the end
of each pin. The “dots” are very
important as they hold the pin’s
connection information. Always
make sure you have actually
connected to the dots when
wiring your schematic.
SCREENSHOT 4. The more information you
enter here, the easier life will be as you
progress through the board layout process.
Note that I have entered the actual Digi-Key
part number in the Order # field.
moved a pair of connection dots on J1.
4) I then went to the PCB and clicked
on the J1 pads.
the toolbar buttons.
An interesting thing happened while I was clicking on
the J1 pads. My design needs to have the top-most pad of
J1 connected to the +9V net. The remaining pads are part
of the GND net. The schematic symbol for J1 did not
match up to my design requirements and the J1 physical
component pads didn’t match up electrically. The
top-most J1 pad was showing a GND connection when
I clicked on it. It should be attached to the +9V net. As it
turns out, the ExpressSCH fix was easy:
1) I removed the connections to J1 on the schematic and
ungrouped J1 as a component.
I repeated the four steps I just outlined until the
ExpressPCB J1 pad layout and the ExpressSCH schematic
symbol matched my design requirements. I used the
highlighted nets to arrange the components as you see
them in Screenshot 9. You have this ExpressPCB file in
your download package. It is led_blinker_B.
Connecting the Dots
Actually, we have already connected the “dots” in the
ExpressSCH phase of the PCB creation process. We are
now ready to begin connecting the pads according to the
2) I then moved J1’s connection
dots — which are the actual pin
connections — to the desired
connecting points on J1 and
regrouped J1 as a component.
3) I rewired J1 into the power
supply on the schematic, saved
the schematic, and refreshed the
link to the PCB each time I
SCREENSHOT 5. This is just an
organizational step. We could
actually add the components in
as we wire them in. This way, we
can ID all of the components and
crosscheck what we have laid
down on the printed circuit board
with the schematic.
June 2008 77
