Description
Circuitron DT-4 Bi-Directional Rolling Stock Detector ~ 5204
The CIRCUITRON DT-4 is an advanced, integrated circuit detection
circuit that can be used to actuate accessories, light panel lamps, etc. The DT-4 uses tiny OptoSensors mounted between the rails to detect a passing train. No modifications to rolling stock
are necessary, and the DT-4 is completely bi-directional. The DT-4 has four independent
detection circuits that can be used separately or together to spot rolling stock at various locations.
The DT-4 outputs are also ideal for triggering and controlling many other CIRCUITRON items.
Revision B of this circuit now has LED indicators on the board for easy adjustment of the
sensitivity controls. The DT-4 is designed to provide simplified power supply connections when
multiple boards are to be connected together by providing power supply input and output
terminals on opposite sides of the board. A section of CIRCUITRON’s Printed Circuit Mounting
Track (PCMT) can be used to provide simple snap-in mounting of the DT-4 or the corner pads may
be drilled out and screws and standoffs used. The DT-4 requires a 10 – 18 volt DC input for
proper operation. A filtered DC supply is preferred. If a source of filtered DC is not available, a
CIRCUITRON PS-1 or PS-2 can be used to convert the output from the accessory terminals of
your power pack to DC. Each output on the DT-4 can control up to 250 ma. of DC current.
CIRCUIT DESIGN: The DT-4 contains four identical, independent detection circuits which operate
as follows: A small amount of current flows through the Opto-Sensor and is applied to one side
of a current comparator circuit. This current is balanced by adjustment of the associated trimmer
(P1-P4). When a piece of rolling stock shades the Opto-Sensor from the ambient room light, the
current decreases due to the increase in resistance, and the output of the comparator turns on.
This output is used to drive an NPN output transistor connected common emitter and will provide
a ground at the output terminal (O1-O4) that is capable of controlling 250 ma. of DC current.
