output of the RTC OSD into a VCR or even a DVR for
recording, then apply 7 to 9 VDC power.
Of course, there is opportunity for customization.
The RTC code could be changed to output in AM/PM
format and the MAX7456 could display it as such. The
MAX7456 code could be changed to alter the
appearance of the characters as custom characters are
supported. Even multiple lines could be displayed, with
one being the title of the camera area and the other
being the date/time.
Bear in mind that the MAX7456 is designed for use
with NTSC and PAL equipment. If you attempt to display
a line at the bottom of the screen — row 16, for instance
— and you are using an HDTV as a monitor, the line will
display somewhere near the middle of the screen
because the MAX7456 will not output past scanline 525
as a 1080p HDTV has 1080 scanlines.
When dealing with high frequency signals, it is often
necessary to include a ground plane. The board that I
created does not have a ground plane, and it was
created using the toner transfer method rather than
having it professionally etched. I found no need for the
ground plane as long as I did not run wires underneath
the board, in which case slight signal noise was noted. If
you’d prefer to have the boards etched professionally,
you might want to edit the Cadsoft Eagle PCB to
eliminate the SSOP to DIP adapter.
If editing is done, be careful not to run any traces
under the MAX7456 because of the exposed pad, unless
you intend to connect the pad. Consider ordering solder
masking and even tinning to make soldering the
MAX7456 a little easier. All of these options can be
quite expensive compared to a basic double-sided board
order, hence I used the SSOP to DIP adapter and saved
quite a bit of money in board etching costs. Although
the dat sheet for the MAX7456 indicates that the
exposed pad should be connected to a similarly sized
pad on the component side of the PD board to aid in
heat dissipation, I’ve had no problems with the chip for
the last several months.
If this board was going to be made into a
commercial product, then a ground plane would
certainly be recommended. In fact, referring to the
MAX7456EVKIT datasheet for a board layout example
would be strongly recommended.
At last check, the MAX7456 was priced around $20
Mouser.com and the DS1302 was about $4. This $20
may seem expensive, but it is worth it for the amount of
time that it saves and the simplicity of use. Also, the last
time that I checked, Maxim has a special program
providing free samples for potential customers that are in
school and have an education based (.edu) email