Autoreverser REV2 for DC & DCC

BLOCKsignalling REV2 DC and DCC Autoreverser

When you want to add a loop to the end of a track, you are left with a problem - as the train leaves the loop to return to the main line the polarity of the main line is incorrect.

If you are operating the layout manually, you can set the points and flip the polarity of the main line and the loco will happily continue.  If you forget either action derailments and shorts can result.

The REV2 autoreverser automates this task, so the points are always aligned with the approaching train, and the polarity on the main line is automatically set to suit (whether using DC or DCC).

The result is the there is nothing to switch (or forget) and the layout just looks after itself.


Single Loop Operation

Infra-red sensors are used to detect when the train approaches the points and automatically set the points and track polarity to suit the approaching locomotive.

In the diagram below, the train enters the loop and travels over sensor 1.   The module senses the train passing over the sensor and sets the points to the mainline (as they are already aligned with the main line, they don't move).

The loco continues around the loop (or it can stop and return to the main line if you wish, passing back over sensor 1).  If it contrinues around the loop, when it reaches sensor 2, the module operates the points motor to set the points to diverging and also swaps the polarity of the main line so the loco can continue the journey exiting the loop back to the main line.

Each time the train enters the loop, it will alternate the direction of travel.

Insulated rail joiners are used as there will be occasions when the track polarities do not match.


REV2 Autoreverser Single Loop

With a single loop, the train does not have to complete travelling around the loop, it can be reversed and leave from the same way it entered.

On DCC layouts, several trains can enter the loop, and depart in either direction as long as care is taken only driving one train out of or in to the loop at a time.


Double Loop Operation

The module can also automate layouts with loops at both ends.

In this case, one sensor is installed on each loop and the locomotives always travel around the loops in the same direction.  You can alter this direction by swapping the wiring of the points motors and repositioning the sensors.

REV2 Autoreverser Double Loops



Power Supply

The module operates from a 12V DC supply (recommended capacity 0.5A or greater).

Please check all wiring carefully before turning on the power to prevent damage to the module.


Terminal Diagram

BLOCKsignalling REV2 Terminal Connections


Connecting the Infra-Red Sensors

An Infra-Red source and Infra-Red detector are moulded into a single 5mm x 6.5mm package that can be located below the track bed to reflect light off rolling stock.

Identify the Sensor 1 leads from the diagram and connect to the terminals marked A1 and C1 on the module.  Leads E and K both connect to terminal G1.

Repeat for Sensor 2, connecting to C2, G2 and A2.

BLOCKsignalling Sensor Pinout

The wires can be extended using small chocolate block and extra lengths of cable if required (not supplied).


Sensor Installation

The Infra-Red sensor is normally installed below the track-bed.  It can also be installed at the side of the track.

BLOCKsignalling Infra-red Detector Side View


The detection range of the unit is up to approximately 25mm from the face of the package.

BLOCKsignalling Infra-red Detector Track View

The detector can be mounted in an 8mm hole drilled through the track baseboard. If required, the detector can be held in place using a small amount of blutack, expanded polystyrene or similar. The led diameter is 2.2mm, so on smaller scales the leds can still have a clear view between the sleepers.



When the power is turned on the points are operated to the normal (straight ahead) direction and the track power is passed straight through.

The points are then switched if necessary to match the state they were in when the module was switched off (and the mainline polarity is also switched if required).

Both sensors now operate, looking for a passing train.

If a train is detected at sensor 1, the points are operated to the normal (straight ahead) direction and power passes straight through the module.

If a train is detected at sensor 2, the points are operated to the reversed (switched) direction and power passing though the module is switched to reverse polarity.

Each time a sensor detects a train, another train cannot be detected until the first sensor is cleared for 5 seconds (to avoid repeated points switching unitl the whole train completely clears the sensor).



Leds can be wired to the Led1 and Led2 terminals (anode to the terminal and cathode to the GND).

Led1 will light when the NORM points output is operated.

Led2 will light when the REV points output is operated.

The leds remain lit between points operation.


Push buttons can be connected to the PB1 and PB2 terminals (common to GND).

Pressing PB1 will actuate the NORM points output.

Pressing PB2 will actuate the REV points output.




If the red led on the module does not flash during operation then check the power supply to the module and the sensor wiring.

If the train leaves the mainline and enters the loop, then stops at the track breaks, it may be that the NORM and REV wiring to points motor needs to be swapped.