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The IRDOT-2D operates a built-in changeover (relay) contact and lights an  LED (same outputs as the IRDOT-2). As a train passes above the IRDOT-2D's sensor the contact and LED switch on and remain on whilst the train is above the sensor. After the train leaves, the contact and LED remain on for a further 4 seconds. This delay prevents the IRDOT-2D continually switching the contact and LED off and on, due to the gaps between the wagons, as the train crosses over it. The delay is also useful when the IRDOT-2D is used for moving trains automatically in storage sidings as it keeps the trains separated.


terminals 2 and 3 connect when detecting a train

When the IRDOT-2D detects a train it lights an LED and operates a contact. Terminals 3 and 4 are connected when a train is detected. Terminals 2 and 4 are connected when no train is detected (LED not lit) The IRDOT-2D is supplied with a 5mm diameter red LED connected to the correct screw terminals. Other colours and sizes of LED can be substituted if desired. The LED provides an aid while installing the IRDOT-2D to check for reflections off obstructions.

After installation the LED can be wired to the control panel. Ensure that the long leg is wired to terminal 5. If several IRDOTs are used all the short legs of the LEDs may be connected together and a single connection taken to one of the terminal 6 connections. The LED will be damaged if it is connected directly to the power supply. It requires a current limiting resistor, this is built into the IRDOT-2D.


The diagram shows how to connect a number of IRDOT-2Ds 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.

train detection with LED and SPDT relay contacts


The IRDOT-2D has a SPDT (single pole double throw) contact rated for currents up to 3 Amps. These contacts have no electrical connection to the rest of the IRDOT-2D circuits,

Automatic storage for a row of trains

IRDOT-2Ds can be wired to move a number of trains sequentially

IRDOT-2D units can be used to control a queue of trains, automatically moving trains up into empty sections. The IRDOT-2Ds also provide LED indication of the occupied sections.

X= IRDOT-2D Position.

The diagram shows 3 storage sections A, B, and C separated by isolation breaks. Each section has an IRDOT-2D positioned at X (no delay is necessary at C so either an IRDOT-2 or IRDOT-2D can be used at this position). Electrical connections from the isolated sections are through a diode and the IRDOT-2D's contacts which go back to the controller. When no train is over the IRDOT-2D the contacts 2 and 4 are connected which power sections of the track through the diodes. (contacts 2 and 4 refer to the numbering of the terminal blocks of the IRDOT-2D). Further track sections may be added to the left.

Suppose a train moves from the left into section C. CPower will be connected onto the track through the contacts until the front of the train is detected by the IRDOT-2D. The contact will then open. If there is no train in section B the track in section C will still be connected to the controller through diode z and section B's relay contact. When a train is in section B the train in section C will be isolated and will stop when it is detected by the IRDOT-2D in section C. When the train leaves section B the train in section C will move up into the next empty section. A train moving into section A will be isolated and stopped when detected. The push button switch  is used to connect power to the track. The switch should be a "push to make" type.When the switch is pressed the train in section A will be powered and leave.


The diodes are used to prevent unwanted connections between the sections. They are one way valves for electricity the band indicating which way the electricity can flow (our diodes are black with a silver band at one end). Looking in the direction a train is travelling; the right hand rail will be positive and the left hand rail negative. Hence for the electricity (current) to flow back to the controller so that the train can move the band needs to be towards the positive rail as shown in the diagram. If the isolation breaks are in the negative rail the diode band would need to be away from the rail. Note that feedback controllers will not work with diodes because the diode prevents the feedback signal reaching the controller. If feedback controllers are used 2 pole relays can be used in place of the diodes. If you wish to use feedback controllers or DCC use the IRDOT-3D instead of the IRDOT-2D.

Controller/train speeds

The train may overshoot the detector if it is running at a fast speed. If this is a problem it may be best to use a separate controller set to a low speed which only powers the storage sidings.

Two trains on oval with stopping at a station

trains can wait at a station and move off when a following train approaches


Two trains are on the oval. One at the station,stopped on the isolated track, the second approaching the IRDOT-2D. When the second train reaches the IRDOT-2D and is detected the IRDOT-2D contact will switch connecting the orange wires and so the isolated rail will become live and the first train will leave the station. 5 seconds after ( due to the delay of the IRDOT-2D) the second train has crossed the IRDOT-2D, the IRDOT-2D relay contacts will open returning the station isolated section to an isolated state.The above will work with both analogue (DC) and DCC.

Some other options are:

If you want the station signal to change to green when the train departs use an IRDOT-3D in place of the IRDOT-2D. The IRDOT-3D has double pole contacts so the second set can be used to control the signal.

If you want gradual slowing and acceleration in the station use a SA7-SB (this will also require 3 reeds or 3 IRDOT-1 detectors) for controlling a longer isolated line in the station. Use an IRDOT-3D positioned similarly to the IRDOT-2D so that when it detects the train it releases 0V from the O/I terminal of the SA7-SB.

For the second train to stop when the first train is departing from the station use an isolation track just after the IRDOT-2D. Position a second IRDOT-2D after the isolation section in the station. When the train reaches the second IRDOT-2D it will switch power to the next waiting train.


Voltage12 to 16 volts, AC or DC

Current consumption 40 m A

Length 3.45 inches 88 mm

Width 1.2 inches 30 mm