■ FIGURE 16. Stepper motor header.
Also included in the article downloads is an
alphanumeric hardware driver. The driver is designed to
drive one to four quad alphanumeric displays. On the
back of each alphanumeric display is an address bus
(solder bridge) that allows you to select a unique address
for each display.
■ FIGURE 14. Alphanumeric display circuit.
through ribbon cables to connect each display.
Since the cable runs are short and the I2C clock rate is
only 1 kHz, the propagation delay should not be a
problem. I know this is not ideal, but the benefits of using
a center point of connection outweigh the extra work of
making a custom cable to connect all the displays together
in a bus.
My driver expects the address to be in a range of
0x70 to 0x73 (decimal 112 to 115). This driver allows you
to send text and numbers to each display by passing a
string to a method. It also can print a sentence across
several of the displays as a ticker. For example, this
ALPHNUM1.TICKERPRINT8(‘THIS SENTENCE WILL
SCROLL ACROSS THE FIRST TWO BANKS.’);
will print the string “‘THIS SENTENCE WILL SCROLL
ACROSS THE FIRST TWO BANKS’ one character at a time
from right to left. The letters will appear to float across the
eight characters of the first two quad alphanumeric
Since these two quad displays
sit side by side, it looks like an
eight-character display, making it
easy to read a long message. This
is great for letting users know
about weather alerts and
displaying system messages during
setup. These displays can be driven
at 5V or 3.3V. I drive them at 5V,
so they are visible and easy to read
in a brightly lit room.
However, they are too bright
for dark rooms. No worries,
though, because the display’s
■ FIGURE 15. Stepper motor schematic.
22 December 2017