For a summary of all the units for controlling 3 and 4 aspect signals please see the 3 and 4 aspect signalling page.

The IRDASC-5 combines block control of signals with built in infra red detection. As a train passes a signal that signal will change to red and each following IRDASC-5 will set its signal to the appropriate aspect ie yellow, double yellow, and green. An LED fixed to the circuit board lights to indicate the operation of the infra red detection for set up purposes.

The IRDASC-5 is available in 2, 3 and 4 aspect versions and these may be used together. For 4 aspect signalling at least four IRDASC-5s are required (with three 4 aspect IRDASC-5s only red, yellow and double yellow would be indicated). Similarly with 3 aspect signalling at least 3 IRDASC-5 boards are required in the oval. When less signals are used or the line does not form a continuous oval a MAS Sequencer operates the last signal in the chain with the IRDASC-5s operating the other signals.

The current board is a redesign of the IRDASC-5. The new board is compatible with the old and functions in the same way but the terminal arrangement has changed.

The IRDASC-5 has all the controls of an IRDASC-4 and works in the same way. However the IRDASC-5 has additional electronics to stop trains at a red signal. This is done by having a short section of isolated track before the signal. Terminals W and X switch power to the isolation section. They are internally connected together by a contact built into the board until the signal changes to red. Whilst the signal is at red W and X are disconnected so switching off power to the isolation section. W and X are completely isolated from the IRDASC-5s power.

IRDASC-5s can be used to allow several trains to run on an oval at the same time. When a faster train gets close to a slower one it will be held at the red signal until the slower train reaches the next block section. You will need at least one more IRDASC-5 than the number of trains that are running so that there is an empty block section for one of the trains to move into. For example if you had 4 IRDASC-5s around the oval then you could have either one, two or three trains running but not four or more trains.

If your model railway has signals interlocked to points you may wish to use the IRDASC-5s as a method of stopping trains derailing at wrongly set points. By interlocking the points movement to the RR terminal the signal will show red when the point is wrongly set and whilst the signal is at red contacts at W an X will be open. These contacts can be wired to isolate a section of track either immmediately before the signal as shown in the diagram, or immediately after the signal for a safety measure just in case the operator does not stop the train. This is known as a SPAD (signal passed at danger.)

contacts on the IRDASC-5 switch power nto a section of track in front of the signal

Positioning the IRDASC-5s infra red devices.

As soon as the front of the train reaches the IRDASC-5 the signal will change to red and the track before the signal will be isolated. The infra red devices therefore need to be positioned far enough from the signal so that the engine pulling the train is clear of the isolation section when it is detected to prevent it being stranded. Note in the diagram the red coloured wire bridges over the isolation section so there is track power carried to the line beyond it

Gradual stops

Trains will stop suddenly when they reach the isolation section. If you use DCC then the train will set off with a gradual acceleration set by the acceleration CV value of its decoder (chip). It is possible to also have gradual braking. There are 2 methods for this. Asymetric braking and brake on DC. Asymetric braking is a more advenced system as the train stops in a set distance rather than slowing at a set rate. In other words regardless of the speed the train is travelling at it can be adjusted to always stop at the signal. Brake on DC slows the train at a set rate so slow trains will not reach the signal and fast ones will overrun it. This will require a set speed for each train to run at if you use brake on DC. Brake on DC is the more widely used on decoders than asymetric braking which is a system introduced by Lenz.


IRDASC-5s may be powered from either an AC or DC supply of 12 to 16Volts. Connect the positive to all + terminals. Connect the negative to all 0V terminals.

Dimensions of IRDASC-5:

Length 135 mm 5.3 inches

Width 32 mm 1.25 inches