Numerous ways to circuit the passing siding. The reed switch offers an advantage over the insulated rail method in that it can select trains which will react. Only those with a magnet underneath will trigger the switch. So for a stop circuit a passenger train can stop at a station while a freight train is ignored. However we will assume that only 2 trains are on the loop in this application. The trains on the passing siding can go in the opposing or same direction.
The center rail on each siding is blocked with fiber pins. Reed switches are placed where the train is to stop allowing for stopping distance and train length. The reed switches could be made to switch power to a relay coil which could latch through one of its contacts. However I would instead trigger a timer with each reed switch,shown is an Infetec single shot,described here.
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Triggering the timer would require much less current and time than a relay coil and increase reliability IMO of the reed switch operation.. A homemade 555 circuit could also be used instead.
The power supply for the circuit is a 10 VAC tap off a transformer. The bridge rectifier and capacitor boost voltage to about 14 VDC for the 12 volt timer and relays.
The timers in turn will power 2, DPDT relay coils (coils 1 and 2 left and center). If reed switch 1 or 2 is made by the train magnet,the timer is triggered, coil 1 or 2 will energize for the time set by its timing resistor ( a 1 meg pot from a few to 180 seconds),then de-energize.
Power from the transformer is routed through the left sets of relays 1 and 2 so that if either relay is on power is cut to the track center rail. This allows for individual set timed periods between train arrival-departure.
Relay 3 is 4PDT (use 2 , DPDT relays in parallel). When relay 1 is energized, coil 3 is energized by relay 1 (right contact set) and electrically latched through its second set in series with the right set (common- Normally closed contacts) of relay 2. When relay 2 is energized the latch is released and coil 3 is de-energized.
The above can also be accomplished with a twin coiled latch relay which would have memory at shutdown. The above would have to be reset manually (Latch restored on relay 3) if shut down while block 2 is vacant. Some twin coiled latch relays do not take constant voltage so the coils would be thrown by capacitor discharge by the right set of contacts of relays 1 and 2.
If relay 3 coil is de-energized track power is on block 1. If relay coil 3 is energized track power is on to block 2. This is accomplished by contact set 1 of relay 3. Both blocks then can not be energized at once.
The third set of contacts on relay 3 would throw the turnouts ,wired in tandem in the proper direction. Atlas switches could be thrown with capacitor discharge.
The optional 4th set of contacts on relay 3 could be used for block signals,wired opposite of each other.
In operation, train 1 would pull into the siding tripping the reed switch,after the set time the opposite train would pull outand run the loop,when it returns train 1 would run the loop. It would not matter if the train stopped dead on the reed switch.
Further relays and voltage dropping diodes could add a soft start circuit. The parts for the above circuit would cost about $55 to make.
Dale H
