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There are six screw terminals at the end of the board

The IRDOT-1 has many uses, it gives an indication of the presence of trains in hidden sidings, inside engine sheds and stations with overall roofs and other locations where the train is difficult to see by the operator. The indication is given by the illumination of an LED which can be wired to a control panel.

The IRDOT-1 is also used to automatically trigger some of our other boards when the train has reached a certain location. Examples are the SA series of boards Timer, Simple Shuttle, IRDASC-1, 2, 3 and the Latching Relay Board.


The IRDOT-1 uses infrared to detect trains. When it detects a train it lights an LED and gives an output for activating other controls. The LED may be mounted on a control panel. It is simple to wire, requiring 2 wires for power and 2 wires for the LED.

The standard version has the infra red detector and emitter soldered to the reverse side of the circuit board. They extend 22mm. The IRDOT-1EW has the infra red emitter and detector attached to the circuit boards by 18 inch long wires. This is to allow the board to be used in locations where it cannot fit directly under the track for example where there are baseboard supports in the way or where the track is raised on a viaduct etc.


As the IRDOT-1 can operate in tunnels and detect all types of rolling stock it is very suitable for train positioning and indicating track occupation in hidden sidings and loops. It is usually best to position the IRDOT-1 at the end of the loop where the front of the train is to stop. Once the "train detected" LED lights the train can be stopped. The IRDOT-1 operates in both light and in the dark.

It is also used to activate automatic controls. For example when used with the SA8 Station Stop it is located at the positions where the train is to start slowing and where it is to stop.


This is as detailed below, but full instructions are supplied with the IRDOT-1. On the photograph of the IRDOT-1 you can see the numbering printed to the right of the terminal block.

Terminal 1 Connects to the positive terminal of the power supply

Terminal 2 Electronic switch (open collector transistor) for connection to our other units such as SA8.

Terminal 3 11 volts output used for relays and undetected LEDs

Terminal 4 Not used

Terminal 5 Connects to the long leg of the LED

Terminal 6 Connects to the negative power supply and short leg of the LED

LED indication

irdot-1 operating train detect and train not detected leds

To indicate when a train is detected a LED is connected to terminals 5 and 6. This LED lights when the train is over the detector. We supply the IRDOT-1 with a 5mm diameter red LED screwed to these terminals. The IRDOT-1 can also operate a seperate LED which lights when no train is detected (green in the diagram). If you wish to indicate no train is present in this way then a resistor (1K) is needed it is screwed into terminals 2 and 3.


a bicolour led can be operated


Alternatively a 3 legged bi colour LED can be used. The diagram shows how this resistor is wired to change colour to give green for no train present and red for train detected. The bicolour LED has the advantage of taking less space on a control panel than two seperate LEDs and is possibly less confusing.

Power supply

Positive power is connected to terminal 1 and negative to terminal 6. If more than 1 board is being used the boards are connected in parallal

The IRDOT-1 can be powered from 12 to 16 Volts either AC or DC. The diagram shows how 3 IRDOT-1s are powered from the same power supply.

Trigger for other modules

The IRDOT-1 is used to activate other units when it detects a train. Terminal 2 will trigger the Dual Timer, IRDASCs, latching relay board, alternate route selector and SA units. This is described in the pages about these boards.


shows connection of irdot-1 to a separate relay

The electronic switch output of the IRDOT-1 will operate many types of relay. A relay of any voltage can be switched subject to a maximum coil current of 100 ma. If the relays coil voltage is 12 volts, it can use the same supply as the IRDOT-1. When operating a relay this way the power supply must be smoothed 12 volt D.C.


shows the infra red emmitter and detector connected by wires to the IRDOT-1 circuit board.

The photograph shows IRDOT-1EW which is the extended wire version of the IRDOT-1. This version is to enable the IRDOT-1 to be used in locations where the IRDOT-1 cannot be fitted directly under the baseboard due to baseboard supports or the track running on a viaduct. The blue and green wire is to the detector and the blue and white to the emitter. The emmitter and detector need to be placed alongside each other. It may help to join them together with some tape.

The IRDOT-1EW can be used in a second way. Rather than reflecting the infra red off the underside of the rolling stock the emmitter can be pointed at the detector, one each side of the track. This will work with the emmitter and detector seperated by a couple of inches up to approx 5 feet. There is more information about this on our "how infra red works page".

Connection to Digitrax DS54/DS64 stationary decoder:

The Digitrax stationary decoder requires an input that changes from less than 6volt DC to greater than 6volt DC. This can be provided from terminal 5 of the IRDOT-1. Use a separate power supply for the IRDOTs. Connect the 0v DC of both the IRDOT and Digitrax power supply together. Remove the LED from the terminal and link terminal 5 to the Digitrax input. An LED train occupation indication can be provided by linking from terminal 2 to the short leg of the LED, then wiring a resistor from the long leg of the LED to terminal 3.

How the IRDOT-1 works and how to install it:

See How infra red detection works


Voltage 12 to 16 volts, AC or DC

Maximum current consumption 25 m A

Length x Width 3.45 x 1.2 inches 88 x 30 mm

Height (Board to highest component) 0.7 inches 17 mm

Height of infrared components 0.9 inches 22 mm