Advanced wiring issue....

[Anonymous]

Ok.. here is a non-beginner wiring question that has us stumped.

We wi***o add a second route to a display trolley layout. The track plan would be operationally shaped like a "y" (as opposed to a "wye" ). We want the trolley to travel from the upper left part of the "y", to the bottom, and back up to the upper right part of the "y", then reverse the whole thing.

So far, our plan is to put a isolated rail at the bottom of the "y" next to the bumper. This will let us know when the trolley is in that location, and it is time to reverse the turnout. Right now, the solution seems to be use a digital flip-flop circuit that drives relays for normal and reverse turnout selection. However, we were wondering if anyone knows of a more "traditional" solution using only relays.

Later, we will add a bit more complexity , by adding turnouts to create a true "wye" and have the trolley travel A->B, B->C, C->A

[Roger Bielen]

Using Gargraves, or Ross, switches there are instructions for connecting them so that they have the "derail" function by having a piece of insulated rail cut in prior to the switch. It seems that it might be possible to use this method with the insulated rail located elsewhere on the circuit to throw the switch.

[lionelsoni]

You will need some sort of 1-bit memory, like a relay or flip-flop. One way to do it with a single relay is as follows:

Use a DPDT relay. Wire the coil in series with a resistor. Connect one end of the resistor to the supply voltage, the other end to one end of the relay coil. Connect the other end of the relay coil to an insulated rail on one leg of the y. Wire one of the normally-open relay contacts to connect that insulated rail to ground (the other running rail), so that, when the trolley operates the relay, it will latch.

Wire the node between the resistor and the relay coil to an insulated rail on the other leg of the y, so that, when the trolley grounds it, it will release the relay. Then use the other SPDT relay contacts to connect an insulated rail on the common (facing-point) leg to one or the other coil in the switch.

The resistor must be able to handle the power when it is connected across the full supply voltage in the relay-releasing action. The relay must be able to operate on the supply voltage as reduced by the series resistor.

(You could dispense with the resistor and the concern with the relay's operating voltage by adding a second relay, operated by the same insulated rail that relased the original relay, whose function is only to provide a normally closed contact to release the first relay by opening its circuit, rather than by short-circuiting it.)

Actually, the "more complex" version is electrically simpler: Put an insulated rail on each leg of the wye, wired to throw the switch leading to that leg to the right (or left, just so that they are all the same). Why not just go all the way to that version?

[lionelsoni]

"ggnagy", I must ask you whether you are the Gregory Nagy that I went to school with in Indiana?

[Anonymous]

QUOTE: Originally posted by lionelsoni

You will need some sort of 1-bit memory, like a relay or flip-flop. One way to do it with a single relay is as follows:

Use a DPDT relay. Wire the coil in series with a resistor. Connect one end of the resistor to the supply voltage, the other end to one end of the relay coil. Connect the other end of the relay coil to an insulated rail on one leg of the y. Wire one of the normally-open relay contacts to connect that insulated rail to ground (the other running rail), so that, when the trolley operates the relay, it will latch.

Wire the node between the resistor and the relay coil to an insulated rail on the other leg of the y, so that, when the trolley grounds it, it will release the relay. Then use the other SPDT relay contacts to connect an insulated rail on the common (facing-point) leg to one or the other coil in the switch.

The resistor must be able to handle the power when it is connected across the full supply voltage in the relay-releasing action. The relay must be able to operate on the supply voltage as reduced by the series resistor.

(You could dispense with the resistor and the concern with the relay's operating voltage by adding a second relay, operated by the same insulated rail that relased the original relay, whose function is only to provide a normally closed contact to release the first relay by opening its circuit, rather than by short-circuiting it.)

Thanks. this is the kind of thing I was looking for. Apparently when I was in school, the thinking was "digital ttl circuits are all these computer types will ever need" and relays treated as a lost art.

QUOTE:
Actually, the "more complex" version is electrically simpler: Put an insulated rail on each leg of the wye, wired to throw the switch leading to that leg to the right (or left, just so that they are all the same). Why not just go all the way to that version?

Yeah, now that you mention that, I see how it is possible. It did not occur to me that the train would allways be taking the same path.

Another trip to the hobby store for more track. =)

ps. Sorry. Not the same Greg. I went to Penn State.