Ialso want to provide a brief update on my recent “reader feedback”
request. At this point, I’ve heard from
more than two dozen readers, and
the results are still very similar to
what I reported last time. Primer
readers seem to be fairly evenly
divided between those who would
rather return to “pure” PICAXE
projects, and those who want to
continue our PICAXE-Pi explorations.
So (as I mentioned last time) I’m
going to continue writing about the
topics that interest me — at least for
the time being.
One reader (Dave Wreski)
provided some important feedback
on our UPS project (June 2014),
which I want to mention here. He
pointed out that I should have
included a fuse for the battery pack
because the D cells are capable of
providing a significant amount of
current. If the voltage regulator were
to fail (and short out in the process),
serious damage could occur. I think
Dave’s recommendation is a good
one, and including an in-line fuse in
the battery V+ line would be a simple
matter.
Finally, a couple of readers have
emailed to ask about the RazzPi
printed circuit boards (PCBs) I
mentioned back in the June column.
(I had a problem with the first batch
of boards that I received, so they
weren’t available on my site when I
said they would be.) Fortunately, I
recently received a second batch of
the first three boards in the RazzPi
series: RazzPi-LCD, RazzPi- 20, and
RazzPi- 14.
The RazzPi-LCD is essentially a
variation of the stripboard interface
board that we have already used,
with the added capability of
attaching a standard HD44780
parallel LCD that’s driven by six
additional GPIO pins on the Pi. The
RazzPi- 20 and RazzPi- 14 are
complete PICAXE project boards that
can be used with or without a Pi.
This month, we’re going to take a
look at two of the RazzPi boards.
Even if you’re not interested in
PICAXE-Pi projects, you may still want
to check out the RazzPi- 20 for
possible use in your pure PICAXE
projects.
The RazzPi-LCD PCB
Figure 1 presents a top view of
the final version of the RazzPiLCD
PCB, which can be directly inserted
into the Pi’s 2x13 GPIO header. In
Figure 2 — which shows the bottom
side of the RazzPi-LCD — you can
see a 2x13 pin female header
running along the lower edge of the
bottom of the board. This header
directly mates with the Pi’s 2x13 pin
male GPIO header, eliminating the
need for a connecting cable. (As an
aside, it should also be possible to
use the RazzPi-LCD board with the
new Pi Model B+ because the first
26 pins of the Model B+ 40-pin
GPIO header are arranged identically
to the older Model B GPIO header.)
In Figure 2, you can also see two
separate headers at the top edge of
the bottom of the RazzPi-LCD, where
you would probably expect to see a
single header for connecting to an
external LCD. We’re going to use a
four-bit data connection for the
external LCD and — as you may
remember — that leaves four unused
pins in the LCD’s 16-pin header.
Rather than including the unused
pins on the RazzPi-LCD, I chose to
eliminate them to save some space
on the board. (On the top of the
Introducing the RazzPi PCBs
Before we dive into the
content for this month's
PICAXE Primer, there are a
couple of things that I
want to mention. First, in
case you haven't heard
about it yet, there's a new
version of the Pi on the
market: the Raspberry Pi
Model B+. It's basically a
re-designed Model B with
several key improvements.
I'll just list three of them
to whet your appetite:
• 40 GPIO pins instead
of 26
• Four USB ports instead
of two
• Micro-SD card instead
of a full size SD card
If you're interested in
learning more about the
Model B+, there's a great
Adafruit.com tutorial you
may want to read. Just
Google "Raspberry Pi
Model B+ Tutorial" and
you'll find it at or near the
top of the list.
■ BY RON HACKETT PICAXE PRIMER
www.jrhackett.net
12 November 2014
