Issue
112 November 1999
Tuning
into the HA Channel
by
Mike Baptiste
A
channel devoted to Home Automation may be a stretch,
but in this month’s column Mike shows us how
to display HCS-II information via television with
a little help from a PIC16C63A and an onscreen display
module named BOB-II.
Start
•
Getting to Know Bob • If
Only It Was That Easy • Command
Parsing • Color Made Easy
and More •
Sources
and PDF
Some
people say the ultimate home automation system is one
you never need to interact with. It should run the day-to-day
functions of your home on its own using sensors and
programming.
I
agree to a point. However, a good home automation system
should also provide homeowners with information about
their home, the status of its systems, or any urgent
events or messages.
Getting
this information usually means bringing up an application
on a PC. People are spending more time in front of their
PCs, but the television is used more often in most households.
Therefore,
I think the TV is an ideal device for presenting vital
home automation information. By adding an infrared interface,
your home automation system can be controlled like any
other A/V device.
I’ve
always wanted to connect my HCS-II to my televisions
(but I wasn’t excited about designing the video
section of the circuit). LCDs are nice for some places,
but they usually aren’t conveniently located and
you can’t see them from across a room.
I
admit it—I’m a bit-head. I can hold my own
when it comes to analog circuitry, but tinkering with
NTSC video was a bit intimidating. Besides, I wanted
it to be easy to build and I had pictures in my head
of dozens of discrete parts making up the video portion.
I
started looking around for chips that would handle onscreen
displays without much external circuitry. I finally
found a few, but they were surface mount and the spec
sheets showed that controlling these OSD chips took
a bit of register manipulation. The amount of code I
needed to write was growing.
It
became apparent that designing the NTSC circuitry wouldn’t
be the hardest part; sourcing the parts would. It was
time to look for something off the shelf.
Third
Party To The Rescue
Recently,
several companies have started selling complete onscreen
display (OSD) modules that enable users to display text
on a television. Communications are handled via a simple
serial interface.
Because
many are self-contained devices, I’d have one box
with a custom controller connected to the third-party
box. Not ideal, but if it worked, I’d be happy.
But, I couldn’t find one that met all of my requirements.
Since
the HCS-II network runs at 9600 bps, I needed an OSD
device that operated at 9600 bps or I’d have to
buffer outgoing data as well as the incoming packets.
Many OSD devices only operate at 1200 bps so HCS data
arriving eight times faster would easily overwhelm the
TV interface.
Video
generation was another drawback of some OSD devices.
Many require external video signals and can only generate
text in monochrome; others don’t allow direct cursor
manipulation. One required sending the row and column
at the beginning of each line displayed.
Given
how most HCS-II LCD interfaces allow moving the cursor
around at will, I needed to be able to move the cursor
on demand when sending one line of text. I began to
wonder if I’d have to brush up on my NTSC and search
for obscure parts after all.
I
had just about given up when I discovered a module called
the BOB-II from Decade Engineering. The BOB-II is a
self-contained OSD device on a 30-pin SIMM. It has a
9600-bps serial port and supports color text—two
of my main requirements.
It
also displays monochrome text over an existing video
signal, generates its own video signal with multiple
color backgrounds, overlays color text on internally
generated backgrounds, and allows direct manipulation
of the cursor position.
