Crossover into a reversing loop

Discussion in 'DCC & Electronics' started by BigJim, Dec 24, 2006.

  1. BigJim

    BigJim Member

    Nov 19, 2006
    Likes Received:
    I am planning on having a crossover with a reversing loop on one side. The other side of the crossover connects to a dual track with a duplicated at the other end. The dual track will always stay connected to the A & B outputs of the DCC as shown with the B output connected to the 12v DC ground..

    I have read that I can switch the phase (phase = polarity with an AC signal) while the train is in the loop without problems. I have also read that the "auto-sense" systems that see a short when a metal wheel crosses a gap with opposite phase on each side can cause small pits in the wheel from the short duration current across the gap. Having a small double gap dead track and switching before the wheel hits the second gap should solve this problem.

    It has been a few years since I worked as an electronic tech (about 35:) ) so I am a little rusty but would like to design and build some of my own special controls rather than just buying black boxes.

    Anybody know if this will work? If there aren't some advantages I am not sure I want to lay the extra 50' of track for the dual track onnection between the loops.

    Flip-flop is just 1/2 of a cross-wired 4001 CMOS quad 2 input nor gate. I don't think the resistors are critical but about a 3 to one ratio (larger value to ground) should result in about an 11 v pulse that will be more than enough for the 8.5 volt maximum set or reset voltage of CMOS at 12v supply (6v nominal). The eight cuts in track are a little hard to see but the diode connections go to a short section of "dead" track between insulated gaps. Since I only need about 4ms for the relay to switch the dead track only needs to be a fraction of an inch long.
    I see four conditions:
    Train enters loop from top track. The positive pulse from track A to diode A will reset the flip-flop (if set and relay on) and turn off the relay so A>O & B>I. The relay will be off by the time the train reaches the second gap so diode B will see ground (track B). Once the relay is off further reset signals have no effect.

    Train goes from loop to top crossover track. If relay is on then diode B will see a pulse and reset the flip-flop and turn off the relay.

    The opposite will be true for the other two conditions on the lower track. Relay turns on with the positive pulse of the DCC signal from to the loop to diode C or from the crossover to diode D.

    The only problem I see is a small operational one. I will have to be careful that I don't have any metal wheels from two trains in the gap area at the same time. DCC shut down time. My previous plan had a single rather than dual track between the two loops with two turnouts so I needed to switch the polarity and throw the turnout every time the train came out of the loop. I guess having the DCC shut down is better than the results of trying to put two trains in the same turnout at the same time:)