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The IRDOT-2 is a circuit board with 6 screw terminals along the narrow end

The IRDOT-2 lights an LED and closes its changeover contacts upon detecting a train. Infra red train detection is used and this works in both light and dark. The contacts are electrically seperate from the rest of the board so can be easily used to operate other electronic systems, electrically they can be thought of as a changeover switch which operates when a train is present. The relay contacts can handle currents up to 3 Amps.

IRDOT-2 infra red train detector for model railway automation shown with its contacts when detecting a train

The diagram shows that, with no train detected, the relay connects terminals 2 and 4.  When detecting a train, the relay connects terminals 3 and 4. As the train detection LED is attached to the board by screw terminals it can be mounted on and wired to a control panel if required.

Automatic stop

the contact is wired to disconnect a wire from an isolated rail to stop a train automatically in a hidden siding

The IRDOT-2  gives precise stopping of trains in hidden sidings. When the front of the train is detected the relay breaks the electrical connection to the track.  A push button switch ("on" when pressed) reconnects the power.  The advantage of this, compared to using a dead section, is that the train stops when the front is detected by the IRDOT-2, and an LED is lit on the control panel to show the train's presence. The isolation section can be any length. The number of wheel pickups or whether the engine is at the front or rear of the train does not affect the stopping position. Wiring the IRDOT-2's LED to the control panel will show which loops and sidings hold trains. To restart the train a push to make push button switch is used to connect the controller to the track.

Alternative to reed switches and magnets.

The IRDOT-2 relay can replace reed switches.  It will operate electronic modules intended for reed switch operation.

Computer interface

As the relay contacts are electrically isolated, it is safe to use them with computer interfaces. This allows a computer to "know" which tracks are empty and when a train has arrived.

Power supply

How to wire a number of irdot-2 infra red train detectorsThe diagram shows how to connect a number of IRDOT-2s to the same power supply.

As the current consumption is low many units can be powered by the same supply. The supply should be from 12 to 16 volts. The units work with either AC or DC. If DC is used the positive connection of the power should connect to every terminal 1. If AC is used it is important to be consistent and connect all terminal 1s to the same power supply terminal.

LED and relay contact and power terminals for infra red model train detector

For information about infra red detection and installation tips see:

How infra red detection works


Voltage12 to 16 volts, AC or DC

Current consumption 40 m A

Length 3.45 inches 88 mm

Width 1.2 inches 30 mm