Computer Control & More
Jim Centanni
FIRST SUBJECT:
My particular interest is in the Delaware & Hudson R.R., since I lived along
the line during the late 30's and the 40's. Naturally, my layout is following
D&H in the steam era. (Those memories are another whole subject!) I have
noticed 3 or 4 others on the net who have expressed interest in the D&H. Let's
at least get together by "USnail.
SECOND SUBJECT:
I have been seriously into computer control of my layout for about two years.
Naturally the first attempt, while operable, has pointed up the need for
better architecture in the interface. It has been totally successful as far as
the areas of sensing, speed control, switch operation, (turnouts), and
operating two trains on a single track layout.
The automation kick started about three years ago when I needed some means to
operate the turnout at the turn around loops at each end of the single track
line. An Infra-red LED/sensor into an LM556 provides the interface and drives
a relay which throws the turnout. Contacts on the switch machine handle
polarity reversal coming out of the loop. Operation has been faultless and led
to the next phase.
The interface between the computer and the railroad begins with a standard
RS/232 communication path. Virtually every computer has or can have such a
serial data port. Hopefully this choice will aid in not re-inventing the
wheel! All interchange of data is in two byte chunks, the first byte being an
address, the second byte being a command value(s).
Addresses in a certain range are interpreted as "read sensor" commands, with
the value indicating which group is to be read from the matrix. The status of
a group of 8 sensors is then echoed back to the computer
Train or car sensing is by means of 32 Infra-Red light emitting diodes and
corresponding I-R detectors. (Three-Five Semiconductors: TEMT880B emitter;
TDET500B detector. Approx. $2.00 per set thru industrial distributors.) These
are arranged in a 4 X 8 matrix and scanned like a computer keyboard, eight
bits or sensors at a time. The use of I-R sensors allows all cars as well as
locomotives to be "seen" by the computer, thus indicating when a complete
train is in the clear at a siding.
The I-R pairs are mounted on opposite sides of the track at about coupler
height. They are at a diagonal to the track to minimize seeing the spaces
between the cars. Small trackside bushes, junk piles and outbuildings hide the
sensors from all but the most searching eyes.
Speed control is by means of a simple 4 bit (16 level) D/A resistor ladder
network. This replaces the normal pot in a pulse width type transistor
throttle. Smoothing capacitors give a smooth transition between levels. Two
throttles are controlled by a single byte, 4 bits each.
Operation of switches, (turnouts), and signal lights, etc, are by transistor
drivers and/or relays, driven in turn by a number of latches or registers.
For reasons of simplicity, the present control program is written in BASIC.
Contrary to some opinions heard in the past, blinding speed is not needed.
Basic has more than ample speed for the monitoring and operation of the
trains. This choice was to permit the use of older and simpler, less costly
computers. I have used both an old CP/M machine with basic on disc as well as
a Commodore 64.
There, I've done it! Someone said we should start writing about what we are
doing and stop haggling over whether to split the group.
LAST SUBJECT:
From time to time, I see articles posted about certain subjects or particular
railroads (read, "REAL TRAINS"), which hit close to my interests. I have been
unable to contact the writers, due to lacking Email facilities. There may be
others who get this stuff second hand and might like to have direct contact.
Would it be too much to ask for posters to include their "snail-mail" address
to permit exchange of special interest info, diagrams, pictures, etc. I will
start it off by closing with mine.
Anyone interested in exchange of ideas and such other treasures which cannot
be easily Emailed, feel free to respond. No promises on how fast I return the
favor, but I will try. [Now if only we had a free FAX net like USENET....]
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Fred B Cupp I personally think
27 Crescent Road that wheels should
Fairport, NY 14450 always have flanges
ph:(716)381-9825
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