(Click on drawing to enlarge)
Infrared
Track
Occupancy
Detector
Circuit
This
is
a
Track
Detector
circuit
that
uses
an
Infrared
LED
Emitter
and
Photo
Transistor
Detector
to
sense
movement
of
traffic
on
a
track.
The
output
has
a
relay
that
can
handle
up
to
5
amps.
It
uses
parts
available
at
Radio
Shack
.
I
have
included
options
for
two
types
of
sensors.
A
below
the
track
reflective
sensor
and
an
above
track
interrupted
beam
sensor.
I
used
the
below
the
track
type
on
my
layout
and
have
included
pictures.
This
sensor
uses
the
one
half
of
a
556
timer
for
a
detector
and
the
other
half
is
a
pulse
stretcher
that
smoothes
out
the
pulse
from
the
cars
going
over
the
sensor.
It
is
set
to
be
about
10
seconds
long.
Reducing
the
value
of
the
1
meg
ohm
resistor
will
shorten
it
if
you
think
it
is
too
long
for
your
application.
This
circuit
can
be
used
in
many
ways
for
throwing
turnouts,
grade
crossings,
signals
etc.
Adjusting sensitivity.
The indicator LED will light when sensor is tripped and is a basically tally light that you can use when setting the sensitivity with the 47k variable resistor. Depending on the amount of ambient infrared light on your layout, you may need to adjust it to just the below threshold of the background lighting. Incandescent lighting has more background Infrared light and fluorescent has the least and therefore is the best to use . As far as using incandescent with IR sensors, it works if you use strategic placement of both lighting and sensors. The problem with the under the track type with they look up into the lighting. Beam interrupter type are not as susceptible to the problem. The under the track type allows a prolific placement of them if you are using them for signaling as I do. Sometimes moving a an Incandescent track flood light a bit will improve the performance of a sensor on the layout. General purpose incandescent fixtures would not cast as intense beam as a track flood and may not be as big of a problem.
(Click
on
drawing
to
enlarge)
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Parts
list: NE556/ML556 Timer IC Radio Shack #276-1728 or Mouser Part 512-LM556CN 1N4001 Radio Shack #276-1101 Matched Infrared Emitter/Phototransistor Set Radio Shack #276-142 or Mouser Photo Detector Part 512-QSD723 Photo Emitter Part 512-QED523 Relay 12 volt DPDT #275-249 10uf 35v ElectrolyticCap. #272-1025 LED (used to adjust sensitivity) #276-307 Variable Resistor 47k (sensitivity trimmer) #271-283 1 meg 1/4 watt resistor #271-1356 270 ohm 1/4 watt resistor #271-1314 15k ohm 1/4 watt resistor #271-1337 470 ohm 1/4 watt resistor #271-1317
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Here are the sensor and emitter assembled together with heat shrink tubing. Note that the sensor also has a piece of black heat shrink on it to act as a light shield. The Infrared light is projected up and reflected off of the rail car's trucks, back into the adjacent sensor. | |
| Here is the assembly mounted in the roadbed of my layout. |  |
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This is what it looks like after ballasting. |