make a custom printed circuit board (PCB) with etchant
solution to solder the SMT FETs and run wires to the LEDs
as they were a bit hard to work with, being so small.
A last minute design addition was to add a single
74HC165 8 bit serial in/parallel out shift register to control up
to eight push buttons for time and date setting capability.
A previous software version allowed the user to bypass
this and set variables within the software using either an
SX-Key or SX Blitz module. This, however, brought an
additional expense for users without an SX-Key or SX Blitz,
but may still be acceptable for a single application.
The case I used came from RadioShack. However, I
do admit that I should have used a larger case as this one
was a tight fit. I have four push buttons I also bought from
RadioShack of which I was able to leave one unused at
the moment for future expansion. The design presented
here only requires three pushbuttons. I also crudely cut an
open face hole in the case using a utility knife and glued a
piece of thin smoke colored Plexiglas to somewhat protect
the display. I mounted an extra power socket and ran the
connections to the SX52 proto board. I was also careful to
place the SX52 proto board towards the bottom of the
case so I could cut out a hole for access for any additional
SX-Key/SX Blitz module programming of the SX52 for future
expansion. Finally, thicker rubber feet (from RadioShack)
are mounted on the bottom of the case for appeal.
(Figure 2) illustrates the complete hardware schematic.
42 January 2009
Larger versions of these
diagrams are viewable at
■ FIGURE 2
SX/B or SX Basic is the compiler Basic used with the
SX52 chip. The latest SX-Key software can be downloaded
from the Parallax website ( www.parallax.com) which
also includes their free SXB compiler Basic 1.51.03. The
program file DS1302_to_LED16x16DisplaySX52_v3B.sxb
is open into the SX Key compiler software. The user simply
plugs their SX-Key or SX Blitz module into the SX- 52 proto
board, applies power to the proto board and associated
LED hardware, and clicks on the Compile button.
In a moment, the user will see a scrolling 06 to
change up or down with the up/down push buttons to set
the hours. Once set, the user presses the next button and
the LED will change color and display a scrolling 30 for
the minutes. This process continues for the seconds,
month, date, year, and day code. The day code represents
the day or the week (e.g., 01 = Monday, 02 = Tuesday, …
07 = Sunday).
This is used because the algorithm in the DS1302
RTC IC only reads a two digit year code, so by telling the
DS1302 what day it is, it will know if it is 1808, 1908, or
2008. (This is pretty smart technology!) Once the time
and date are set by the push buttons, the user can just sit
back and enjoy the scrolling display.
The software basically repeats the scrolling of the time
on the top eight rows of LEDs and the date on the bottom