SMILEY’S WORKSHOP ☺
I then noticed
something that I
should have seen
earlier (had I been
The battery wires
will cross each
other on their way
to the DS1307
require either two
layers or some
Also, the I2C wire
on the left to R1
from the Arduino
enough room to
be routed. So, I
flipped the battery
moved the resistors up, and tried again.
In Figure 17, we see my first finished wiring attempt.
I couldn’t figure out how to change the grid size, so I shut
it off and carefully routed the wires. As an experienced
PCB designer, I immediately noticed something quite
scary. Wires on a PCB are called traces. The traces and
the pads on the right of the DS1307 look like they short
out. In my experience, I can set the size of the traces and
the parts pads so that I would normally be able to route a
trace between IC pins, but it sure doesn’t look like that
will work here. Will this mean that I’m going to have to
use two layers so that I can drop those wires to the
bottom, and route them up and over?
Well, let’s hope what Fritzing is showing us isn’t what
it generates for the final PCB file. So, click on the ‘Export
for PCB’ and the ‘Etchable (PDF)’ as shown in Figure 18.
This gives us five PDF files — one for each layer. Let’s look
at the ‘…etch_bottom_copper.pdf’ shown in Figure 19.
See those red circles? Yes, we have a problem!
Okay, I’m used to being able to set the pad and trace
dimensions, but Fritzing doesn’t seem ready for that. Let’s
reroute the troubling traces on the opposite side and see
what we get.
To fix this, we click on the problem traces and
change the side from bottom to top as shown in
Figure 20. Then, reroute them up and over to the
battery terminal BUT notice that we still have a problem
since these traces will have to cross — unless we flip the
battery terminal back like it was to begin with (sigh!). The
results are shown in Figure 16. Yes, I could have shown
all this in the correct order to begin with, but I think it is
helpful to see the actual problems I ran into and how I
fixed them. The resulting top and bottom layer are shown
in Figure 21.
Actually, take a long hard look at Figure 21. Ask
yourself if this is the final wiring or could you perhaps
■ FIGURE 10. Fritzing may
■ FIGURE 11. Align to Grid.
■ FIGURE 12. PCB parts on the grid.
make some minor changes and get all the wires on one
side of the board. Well, it’s possible, but since my goal
here is to produce a PCB design that can be sent to a fab
house (where someone else will do the work), we’ll just
I have to say that making a board with all that free
space and the entire upper row of Arduino pins gives me
the creeps — so much wasted space. Since we are making
an Arduino shield we actually need all those pins so that
we can — theoretically — mount another shield on top of
the one we are making. [BTW, I found that you can — in
September 2012 71