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Automatic train control

with SA boards


We have a range of units to provide many different types of automation for different track plans. These units automatically control trains, signals and points. These can provide automatic operation of a branchline, one or more trams running in the background or even very complex automatic model railway. It is also possible to arrange parts of a layout to be switched between automatic and manual operation so if you wish you can sit back and watch your trains run themselves.

All these units with the SA prefix (which is for Slow Accelerate) have gradual and adjustable braking and acceleration. They work from any power supply from 12 to 16 Volts either AC or DC although they do not require units can automate all or part of a model railway. The units give a gradual and adjustable acceleration, braking, and speed and operate signals and points automatically. Overload current protection is provided to protect the units and locomotives from being damaged by short circuits resulting from derailments etc. Points and signals are controlled with relay contacts from relays built into the boards. The point control works in the same way as the IRDOT-P. Contacts close for 1 second to power solenoid point motors. LED or bulb signals can be operated. The signal output can also switch devices to operate semaphore signals. Some boards have the suffix DSS. These have outputs designed to operate Dapol semaphore signals.

Units can be combined together to give more complex operations. For example you could have hidden storage sidings operated by the SA6 and a SA5-S passing loop controller or SA8-S station stop in the visible section. Passenger trains would stop after a gradual braking and goods trains run through non stop with the signals changing correctly and a succession of trains appearing from the hidden section.

The SA units need to know where trains are so that they can start slowing or stopping the trains. Either IRDOT-1s or reed switches can be used for this. The advantage of using IRDOT-1s is that the front of the train is always stopped at the correct place. With reed switches the train is stopped when the magnet arrives over the reed switch.


The SA boards have adjustable acceleration braking wait time and speed

All the SA units have gradual acceleration and braking built in. Each board has the following screwdriver adjustments:

WAIT TIME: This adjusts the length of time between trains arriving and departing.

MAXIMUM SPEED This adjusts the fastest speed the train reaches.

MINIMUM SPEED: The minimum speed setting is provided so that the train will stop at exactly the right place. When the train slows, it slows to the minimum speed setting, not to a stop. This allows it to continue moving slowly until it is detected at the stopping position. Power is then switched off the track by the SA board.

ACCELERATION/BRAKING:This adjusts the rate at which speed increases or decreases. The length of track over which this happens can be from a few inches to approx.10 foot.


The SA boards have a red and a green LED. These show what the SA board is doing.

RED LED lit: train is braking or travelling at minimum speed.

GREEN LED lit: train is accelerating or travelling at maximum speed.

RED and GREEN LED's flashing alternatively: SA board is timing the adjustable delay between one train arriving and another departing or a train waiting at the station. The longer the flashes the longer the delay.

RED and GREEN LED's BOTH LIT: There is an overload on the track caused by a derailment or short circuit. Current is automatically cut off from the track until the short circuit is removed. This safety feature protects both the SA board and the locomotive from damage.

Switching between automatic and manual control

To switch between automatic and manual control a DPDT ( Double Pole Double Throw) switch is used. Throwing the switch connects either the SA boards' output or the controller track output to the track. If a DPDT centre-off switch is used the central position of the switch will isolate the track. If the SA board also controls points then manual switches may be wired to the point motors. An on/off switch may also be required to disconnect the point motors' power supply from the SA board. This prevents the SA board switching the points as trains are manually driven over detectors. Switching between manual and automatic model railway control

The solder tag side of the DPDT switch is shown in the diagram. The following lists all the SA units, several have a link to their own webpage giving a very detailed explaination.

SA1 Single line shuttle

The SA1 operates a branch line shuttle service. A train runs backwards and forwards over the line gradually slowing as it approaches the ends of the line. Four train detectors are required e.g. IRDOT-1s or reed switches. A detector is at each end of the line to tell the SA1 where the train is to stop. Detectors are also positioned where the train is to start slowing down. It is possible to add sidings at one or both ends using IRDOT-Ps to switch the points, so allowing any number of trains to alternately run backwards and forwards between the sidings. The IRDOT-P "P" terminals will replace the train detectors at the ends of the lines.

SA1-S Single line shuttle with signal control at each end

This works in the same way as the SA1 but with controls for a starter signal at each end of the line. Four train detectors are required.

SA1.1 Single line shuttle with station stops

Shuttle with intermediate station stopThis unit works in the same way as the SA1 but allows one or more intermediate stations to be operated. Each of these station stops can be operated with two train detctors as the start slowing detector for one direction becomes the stop detector for the other direction. The SA1.1 can also be wired so trains stop in one direction but not the other. Four train detectors are required, plus two train detectors for each station stop in each direction. Sidings can be added at one or both ends allowing extra trains to alternate up and down the line. These require IRDOT-P units.

SA2 Single line shuttle with a siding at each end of the line

Operates as the SA2-S but without signal control.


SA2-S Single line shuttle with a siding at each end and two starter signals

Shuttle with siding at each end and two strter signals at one end

Two trains run alternatively along a single line. As the train approaches the end of the line it gradually slows then stops. There is an adjustable delay, then the point changes to the other siding, a short delay, the other sidings signal sets to clear, a short delay and the second train slowly accelerates away. Six train detectors are used. Two at the "start slowing " positions and four for the stopping positions at the end of the sidings. The SA2-S controls two signals. These signals operate for trains leaving both sidings at one end of the line.

SA9-S Single line shuttle with siding at one end and control for two signals at the siding end.


SA9.1-S Single line shuttle with siding at one end and control for one signal at the single track end


SA10 Single train shuttle on single line with siding at one end.

The SA10 operates a single train with two sidings. The train shuttles up and down the line alternating between siding 1 and siding 2. There is an adjustable delay at each end. 5 train detectors are required. One use is to give a shunting effect, it would be possible to add to the number of sidings by using the Alternate route selector.


The SA12 operates a single line train with a reverse loop at one end.It requires two IRDOT-P's and one IRDOT-1 For a point operated by a solenoid point motor (Peco, Seep etc) train detectors at D1 and D2 are IRDOT-P. The train detector at D3 is either an IRDOT-1or reed switch. For a spring point the detectors at D1 D2 and D3 are either IRDOT-1 or reed switches. Insulation breaks are necessary for the reverse loop. The SA-12 feeds the reverse loop with a constant polarity and switches the polarity to the straight section.


As SA12 but with the addition of relay contacts to operate a starter signal which can be either bulb or LED.


This has a passing loop in the middle of the shuttle. Two trains run alternatively. They cross at the passing loop. Eight train detectors are required.

SA4 Passing loop for oval-opposite direction trains

automatic passing loop operation for trains travelling in opposite directions on the model railway ovalTwo trains run alternately around an oval. Each waits at the passing loop for the other train to arrive before, after an adjustable delay, departing in the opposite direction Point switching relays are built into the unit. Four train detectors are required. The slow detectors may be positioned before or after the points.

SA4-S Passing loop for oval - opposite direction trains

This works as the above with built in contacts to control the two starter signals at the ends of the loops. These signals are normally at red. At the end of the adjustable delay the points change there is a pause the signal sets to clear another pause and the train accelerates away. A few seconds later the signal returns to red.

SA5 Passing loop for oval - same direction trains

Two trains run alternately around an oval. Each waits at the passing loop for the other train to arrive before, after an adjustable delay, departing in the same direction . Point switching relays are built into the unit. Three train detectors are required. Two or more SA5 units will operate on the same oval. The SA5 can also be combined with the SA8 station stop or SA6 storage sidings.

SA5-S Passing loop for oval - same direction trains

As SA5 with control for starter signals at the end of each loop.

SA5-PB and SA5-SPB

Push Button operated versions of SA5 and SA5-S. This is suited to display layouts. The trains wait in the passing loops until a member of the public presses a pushbutton. The two trains then run a number of laps before waiting in the station for the push button to be pressed again.


>See Storage_Siding section. The SA6 can be combined with an IRDOT-1 and IRDOT-Ps to provide automatic storage siding operation on an oval.

SA6-B Storage sidings

Block control for storage sidings. See Storage Siding section.


Forms a block section. See Block Section.


Forms a passing loop block section. See Block Section.


Forms a station stop block section. See Block Section.


SPECIFICATION Voltage 12 to 16 volts, AC or DC Inches Millimetres