EXTRA FEATURES OF THE IRDASC
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"OVERRIDE/INTERLOCK" (OI) TERMINAL
As well as its use for block sections this terminal provides: 
1 INTERLOCKING TO POINTS:     
   This causes the signal to stay at red when trains approach if a point is wrongly set.  It is useful at junctions.
2 MANUAL OVERRIDE: 
   A switch can be operated to cause the signal to stay at red for trains stopping at a station.  Similarly the relay of the Dual Timer can operate the "OI" terminal.
The override/interlock terminal operates when connected to 0 volts.  To experiment fasten a piece of wire on to terminal 6 then touch the override/interlock terminal with the wire. If the signal was at green it will change to red.  Removing the wire returns the signal to green.
Points and signals are interlocked by wiring the override/interlock terminal to a contact operated by the points movement.  The contact is wired to connect terminal 6 to the over ride/interlock terminal when the points are wrongly set.  When the point is correctly set, no connection is made.  A toggle switch can also be used to connect terminal 6 and the override/interlock terminal to give manual control of a signal at a station. The switch is operated for stopping trains causing the signal to change to red until the switch is released.  For through trains the switch isn't changed and so the signal changes to green for approaching trains.  A double pole switch can be used; the second pole isolates the track in front of the signal. 
To make the signal remain at red when the next block section up the line is occupied; connect from the "train in section " terminal of the next IRDASC to the override/interlock terminal.
Many wires can be connected to an override/interlock terminal.  When any one of these connections operates the override/interlock terminal it causes the signal to remain at danger for approaching trains.  The signal will only change to green when none of these wires is at 0 volts. 
"TRAIN IN SECTION" TERMINAL:
When the IRDASCs block section is occupied this terminal switches to 0 volts.  See " block section" above for an explanation.
"REVERSE RUNNING" (RR) TERMINAL:
This terminal is used to allow correct signal operation when there is bi-directional running along a line.  When a train is to run against the signals the reverse running terminal sets the signal to red.  Unlike using the override/interlock terminal the "reverse running" terminal clears the IRDASCs memory of a train in its block section.  If this input is not used then a reverse running train will cause each IRDASC to detect a train leaving the block section before the train entering section message; the result of which is to wrongly leave each signal at green after the train has left the block section.  The "REVERSE RUNNING" terminal can be activated with a changeover switch.  It can also be operated automatically with the Train Direction Detector.  A single Direction Detector or changeover switch will operate all the "reverse running" terminals of a chain of IRDASCs.
The "RR" terminal has a second use as a reset to set all the signals to red.  In this case all the reverse running terminals are connected to a single push button switch.
"TRAIN IN SECTION LED":  
This terminal is used if you wish to have a signal box style illuminated track diagram.  The terminal lights an LED whilst a train is in the block section.  As trains travel around the layout you will see each LED lighting in turn as the train travels from one block section to the next.
ISOLATING THE TRACK WITH THE IRDASC-3:
The IRDASC-3 can isolate the track in front of a red signal.  Power is switched onto the track when the signal is green.  Hence trains will be automatically stopped by the signal if the points are incorrectly set; the next block section is occupied etc.  Relay contacts (rated at 3 amps) isolate the track so keeping the track, signalling and IRDASC electrically separate.  The isolated section should be just in front of the signal where the engine is to stop and slightly longer than the longest engine.  For bi-directional running a diode will feed current into the isolated section for trains running against the signals.
Several trains can be run on the same line by using a number of IRDASC-3 controlled block sections.  When one train begins to catch up with another it will automatically stop at the next signal until the next block section is empty.
AUTOMATIC CONTROL OF A QUEUE OF TRAINS IN HIDDEN SIDINGS:
Where two or more trains are stored on a long hidden siding IRDASC-3s can be used to make the trains move up one position when the leading train leaves.  A switch connecting 0 volts to the "override/interlock" terminal will control exit from the storage sidings.  The IRDASC 3 will isolate the track when the switch operates.
DIMENSIONS OF THE IRDASC:
The IRDASC-1 measures 31 mm by 128 mm.  The IRDASC-2 and IRDASC-3 measure 31 mm by 137 mm.  Component heights are the same as the IRDOT
ELECTRICAL OPERATION OF SEMAPHORE SIGNALS:
The IRDASC-2 or IRDASC-3 can operate Semaphore signals.  Instead of bulbs these boards will switch low current solenoids, memory wire or a relay with a moving arm (our relays are not suitable) to move the semaphore signal.
JUNCTIONS:
Both facing and trailing junctions can be correctly signalled.  Signals, points (and even isolating sections if the IRDASC-3 is used) can be interlocked.  This is explained in detail in the instructions.
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