SCREENSHOT 2. As you can see,
there are lots of ready-to-place
components to choose from. Using
these ready-made schematic
images ultimately makes laying out
your printed circuit board easier
as each schematic image in the
ExpressSCH catalog can be linked
to a similar physical component
in the ExpressPCB catalog.
information up front makes things easier at the back end
of the PCB layout process.
Our design consists of a PIC18F2620 (U1), an ICSP
portal (J1), four LEDs (LED1-LED4) with associated current
limiting resistors (R4-R7), and a power supply. There is no
crystal in this design as we can call upon the PIC18F2620’s
internal clock. The power supply is a classic linear
regulator-based + 5 VDC circuit. There is no rocket science
here. All we want this circuit to do is blink the LEDs.
If you peek under the Edit pull-down menu, you’ll find a
method of generating a BOM (Bill of Materials). I punched
our BOM into the Excel spreadsheet you see in Figure 1.
Our logical layout in
Schematic 1 has been tested and
is complete. Now we can begin
to do what we all came here to
do: lay out the printed circuit
board. You will find that the
ExpressPCB application looks
and feels like the ExpressSCH
application. I clicked on the
Place a component button in the ExpressPCB application
and selected all of the physical components that exist
in Schematic 1 as logical components. I arranged the
physical components according to their functional area in
Screenshot 5. I then activated the File pull-down menu
and linked our ExpressSCH led_blinker schematic to the
ExpressPCB led_blinker PCB layout.
I prefer to work with a PCB grid of 0.025 inches.
Again, just as we did in the ExpressSCH application, I
activated the ExpressPCB View pull-down menu and
selected the Options entry. The rest of the story lies within
the Options window you see in Screenshot 6.
Now is a good time to associate the PCB components
with their schematic equivalents. A double-click on
the right-most resistor under the RJ- 11 jack reveals
Screenshot 7. As you can see in the Screenshot 7
Component properties window, I associated the resistor
with R1 in Schematic 1. Repeating the double-click
trick on every component resulted in what you see in
Screenshot 8. I have provided Screenshot 8 as an
ExpressPCB file called led_blinker_A. Load up led_blinker
_A and make sure it is linked to Schematic 1. Click on the
Highlight net connections button. Then, click on
various connection points of the components laid down
on the printed circuit board. The connections between
the clicked component and the other components
will be highlighted. I’ll use the highlighted net display
as a tool to assist in logically laying out the components.
It’s also a good practice to learn the toolbar button
shortcut keys. For instance, simply pressing “N” on the
keyboard will put you into Highlight net connections
mode. You’ll find that being able to keyboard into a
mode is easier than pointing the cursor and clicking on
FIGURE 1. The ExpressSCH application allows you to copy
the BOM data to a file. I used the Excel import function to
suck the BOM data into the spreadsheet you see here.