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Posted By lownote on 02/24/2008 6:46 AM

I would like to set up a crossing, so the eggliner track crosses the mainline. But I want an auto stop for the crossing, so the eggliner would stop when a mainline train was in the crossing. I need to keep the egg liner track on its own power supply. I think toddallin's bump a.s.s. system won't work, because it relies (as far as I can tell) on both tracks in the crossing being on the same power supply

Bump A.S.S. was designed to work with one or two  separate systems.  Makes absolutely no difference.  (I actually use it with three systems, though only two are used at any given time.)

I assume that you are referring to the original Bump A.S.S. and not the new revised simplified relay system I conceived a couple months ago.




The Tortoise Bump Accident Avoidance System (Bump A.S.S.) was designed to protect a 30-degree crossing where two trains running on separate loops would meet. This system draws off track power and makes trains wait for opposing traffic. As designed, the system works down to about 6 volts on the rails, so is fine for anything but an extremely slow crawl.  The system can be changed so that it can operate off its own power supply (even just a 6-volt battery) so trains can run at any voltage.

The system includes two detector and two timing circuits that are based on the 555/556 timing chip.

The detectors consist of short sections of rail sandwiched between Aristo-Craft track insulators. The rail is only long enough to fit in the gap between the two insulators pressed together, so any power loss to a wheel is VERY short (less than half of a turn-out frog). This rail has a feed to a bridge rectifier. The other side of the bridge is fed from the opposite rail. (I use the "common" rail). The sections of track leading to/from the insulated section have a jumper under the insulators to maintain continuity. When any metal wheel crosses the gap, it sends a pulse of electricity to the bridge rectifier.

The power from the bridge is fed to a 6-volt voltage regulator and this triggers a 6-volt relay. That's the detector circuit, plain and simple!!! Two are needed and they are installed on all four sides of the x-ing and are wired in parallel in groups of two for the two sets of tracks. They need to be about 3 feet before the crossing to allow traffic time to skid to a stop prior to smacking opposing traffic already in the x-ing. They also need to be installed far enough from the prior blocks to keep an engine/tender combination from routing power from the prior block through bridging through the wheels. If you are not using lighted cars or double/triple heading, 3 feet is probably plenty.

This relay pulse must then me "latched" and timed to allow for a train to pass. A 556 (twin 555s in one case) timing chip is used ($0.69 each Internet surplus or $1.50 at RS), but could be two 555s. With a couple resistors and capacitors, timing can be set at any length (from milliseconds up to several weeks).

A rectifier is also connected to the powered rail (actually input to the "block" being protected) and the common rail. This also feeds a 6-volt regulator that powers the 556 and subsequent relays/LEDs. The relay in the detector serves as the trigger to the 556 and when closed by the wheel bridging the gap, it starts the 556 timing. The 556 closes a 4.5 to 6-volt relay. The input to the blocks being protected is routed to the N/C contacts of the relay. When the relay is activated, it open the circuit to the opposing block and the opposing train stops prior to collision.

Using other contacts on the relay, the system includes green/red LEDs that show the status of the block and these are set up as target signals on the layout and on the structure that houses the system for instant verification of system status. I actually get yellow between the green and red signals by having the relay connect the green portion of the LED to a big capacitor when the signal changes to red. The cap keeps the green on for a moment and the combination of green and red produces yellow. These LEDs are also powered off the 6 volt regulated supply that feeds the 556.

BTW, if you are electronically and/or monitarily challanged, almost all of the parts (except the two relays, the chip,  a couple resistors and a capacitor) can be replaced with a simple 6 volt wall wart and the system will work regardless of the voltage applied to the rails.  ;) 
 

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Not at all.  The Bump A.S.S relay would go between the reverser and track and will have no effect on the reverser's cycle.
 
However, if the eggliner stops and waits for a train, while the reverser shifts, it would just go back the way it came without ever making it to the destination point.
 
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