FIGURE 3. My DIY HP- 45
calculator using two MAX7219
ICs to make this colorful
10-digit numeric LED display
by just wire-wrapping each
LED segment to the
MAX7219 driver.
compared to a numeric LED
display that we covered
previously in these articles.
Another novel use for an
LCD is to obtain status
information remotely with teleoperated VEX models. This can
be accomplished by using the
VEX RC and wireless video
camera to take advantage of an
LCD display placed in the
camera’s field of view to visually
monitor the robot status from a
distance.
We will talk about how to
interface a low cost LCD display
and program it using PIC18 C,
but for those readers who want
to build it to simply see how
LCDs work, just follow the
simple instructions given here to
build the four-bit parallel bus
LCD display. Although it uses
more I/O pins than the IFI
offering, it costs less ($14.99
from SparkFun.com).
TABLE 1. Subset of the commands that can be sent
to the standard Hitachi HD44780 LCD controller.
Command Name Value
LCDCMD
254
LCDCLS
1
LCDHOME
2
LCDLINE1BASE
128
LCDLINEINCR
64
LCDSCRLRIGHT
28
LCDSCRLLEFT
24
62 SERVO 06.2010
Using an LCD Display for Debugging VEX C Applications
Debugging and testing VEX C applications can be
difficult when not connected to a computer since the only
clues to the robot’s bad behavior is its movements or lack
thereof. In this case, carefully placed printf messages to the
LCD can provide some insight into what has gone wrong by
displaying specific diagnostic information, including the
latest motor commands that were sent to it and the latest
sensor readings.
Be sure to add appropriate pauses between lines of
text sent to the LCD by using the pause function provided.
This way, the user gets a chance to read the message
before it’s overwritten by the next message.
