Hi - I was trying to use some 670's to trip my switches, but they are weak and don't fire reliably. (These 670's draw current, a two-powered engine train would throw the frog twice, the second time is redundant, I occasionally do that anyway by accident.) They look like a "U" and clamp on the track. The two branches going into the main wye switch should be auto-throw once going "in", no response coming out. For the loop, once-per-train fire (I run no more than 3 powered SD-90's at a time or two powered A ABBA Alcos), same within the loop, if you think of the engine in the middle of the loop, in one direction it should fire one switch position, in the other direction the other.
Some sort of timing latch would be ideal, the first engine fires it and the rest pass in say 15-20 seconds without further tripping the sensor. I'd put the hot side of the accessories on one side of this device and use it to run the switches via the red and yellow switch connection terminals.
So infrared, current draw, proximity sensor - I'm looking for a single "entity" that maybe has a latch (fire once) that can tell simple direction. I've looked at the Dallee stuff, I don't like their descriptions of how things work, I figure I'd tap the knowledge here. My layout is almost all AF, I don't want to use fancy control system, just simple stuff (like the author), for instance I gave up on the AF reverse loop relay because the relays don't fire reliably, I replace them with Atlas snap-relays and this worked out just fine for the wye and loop, to that I'm adding this "directional switch throwing" and hoping someone knows of something that works.