PICAXE PRIMER
■ BY RON HACKETT
SHARPENING YOUR TOOLS OF CREATIVITY
YET ANOTHER LED-2X7 PROJECT!
When we completed our
experiments with the
MCP9700A analog
temperature sensor in the
previous Primer
installment, I was sure
that we had also
completed our discussion
of two-digit, seven-segment LED displays.
Well, I was wrong! Shortly
after I finished the
MCP9700A article, I was
searching for something
on the Web, and I
happened to read some
information about the
Lumex LDD-N514RI-RA
two-digit LED display. The
pinout of this display
almost perfectly matches
that of the 20M2 — so
naturally, I couldn't resist
experimenting with the
new possibilities. As a
result, I hope you're ready
for yet another LED-2X7
project! Even if you aren't,
I would encourage you to
continue reading, because
this one is going to lead
us into a very interesting
and powerful feature of
the M2-class processors.
Before we begin our exploration
of the N514RA display, I want to give
you a quick update on my 4.5V
(three D cells) battery-powered 20M2
project. When I first powered it up,
the battery voltage was 4.8V. It has
been happily blinking 24/7 for exactly
two months now, and the battery
voltage is currently 4.5V. So, things
are looking good.
When I finish this installment of
the Primer, I plan to add some
circuitry to the board in order to
increase the current consumption,
and then see how the batteries
perform. I'll provide a second update
in another couple months.
THE LUMEX
LDD-N514RI-RA
LED DISPLAY
Let's begin with the pinout of
the N514RA which is presented in
Figure 1. As you can see, the display
only has 10 pins, rather than the 18
pins that we've been working with
recently. In our previous projects, we
simply grounded the display's two
common cathode pins, and output
the data for both digits
simultaneously. However, that
approach won't work with the
N514RA. If we connect both
common cathode pins directly to
ground, the same digit would be
displayed in both digit positions. In
effect, we would have a very simple
■ FIGURE 1. LDD-N514RI-RA LED display pinout.
50
February 2013
