I would like to investigate the feasibility of utilizing a serial
connection (from a PC) to turn on/off up to 80 lights/other devices.
This circuit to decode the serial signals (hopefully to a TTL Level)
would be up to 15 feet away from the PC with leads to the
lights/devices emanating from that. Turning on/off the lights/devices
electronically isn't outside of my knowledge level, but utilizing a
serial format to trigger the circuit/s is.
Is there a solid state device that will decode serial patterns written
from the PC, and activate only when a specific pattern is detected, or
would a different approach be more practical?
I'm not married to a serial format, and would entertain another
protocol such as USB, etc.
Thank you in advance for any suggestions, or web site URLs.
Here is a supplier of equipment that will do what you need. You may have to
use 485 instead of 232 for your serial comm. This companies products are
very well respected and widely used in industrial and utilty settings.
Thank you for the response, and so quick!
I appreciate the URL, and you are correct this system would do exactly
what I'm looking for and more. However, I would prefer a more
experimenter/discrete approach as this is more of an opportunity to
learn about the subject in a hands on mode, and in an economical
I recall some time ago reading about a small IC that could be
configured to decode bit patterns on a serial line, and then provide an
output when that specific pattern was detected. I have searched the
net, but can't find any reference to such a chip. :o(
Very interesting URLs, and these units also appear capable of doing
what I'm after, but the cost of assembling enough modules to switch 80
different lights individually still seem a bit out of the range of the
At first I intend to utilize LEDs for the indicator lights, and later
if it works out ok I would add triacs to allow increased wattage level
Thank you for the response!
Lookup Serial Comparator Circuits and see if something like that will
do what you want it to do. Typically, you would build your circuit of
multiple components (shift registers, memory, logic gates AND, OR,
NOR, and then output to Darlington pairs or Triacs for extra power
etc. ) although there may be one chip that "does it all".
There are very many approaches to this! Whilst the ones of
using shift registers are excellent, I am going to suggest
something rather different, which seems to fit better with
what I think you are thinking of ;)
I suggest that you look at PIC Microcontrollers. These can
be very very inexpensive and very simple to design with.
You could make a PIC module, with a row of DIP switches on
it to specify its address, and with a serial-in and a
serial-out port. The PIC module reads data on the serial-in
which is daisy chained from the PC through as many modules
as you want. If the first two words match the address of a
particular module, it uses the next word as control for its
lamp(s). If not, it passes the words out on its serial-out port.
Modules could be of just one or two types (although you
could add many other types):
Type 1 gives 256 different light settings for a single
output. It uses the first two words as address and the third
word as intensity.
Type 2 gives on/off settings for up to 8 outputs. It uses
the third word as on/off for each of the outputs.
You could mix and match these modules and expansion would be
easy - just add more modules on the daisy chain.
This would be very,very easy to program from the PC. You
could just use Hyperterm and type in characters equivalent
to the three words, for testing. You could have a text file
containing all the changes and just send it to the serial
port, character by character - with gaps as needed, to
operate. For testing again, you could slow the bit rate
right down and see each light change.
There would be a "ripple" effect because not all the outputs
are changed simultaneously, but, with a high Baud rate on
the serial line, this wouldn't be apparent.
Sorry to other posters if this has already been covered in
one of their links, but I haven't the time at the moment to
go through them all (and this computer is a Pentium 90...).
Rather a fun project!
Am I the only model railroader here? Take a look at Bruce Chubb's C/MRI
(Computer Model Railroad Interface) at
really a general purpose input/output system using a serial interface,
RS-232 for a single node or RS-485 for multiple nodes. The User's Manual
includes Quick Basic and Visual Basic example programs with all of the
communication code. You can also download the free JMRI (Java Model
Railroad Inteface) software at
and use Panel
Pro to build graphic control panels and communicate with the C/MRI