I'm not sure than I understand Mike's arrangement of control and stop blocks, but I think it might be something like this: The control block precedes the stop block. Train A waits in the stop block until train B, approaching from the rear, enters the control block. This operates the relay, removing power from the loop generally and supplying power to the stop block. Train B therefore stops and train A starts up. As train A leaves the stop block, it supplies power momentarily to the layout generally, causing train B to start and move off the control block. As train B moves off the control block, the relay releases, restoring power to the layout generally and removing it from the stop block. Train A then proceeds around the loop while train B moves into the stop block and stops. Then the process repeats with the roles of the two trains swapped.
Perhaps this is not how Mike's design works; but the scheme that I just described seems to need some careful tuning of the block locations and the train lengths to work. For example, if train A doesn't bridge the gap long enough when leaving the stop block, both trains stop. And, if train B is too fast or too close to the rear of train A, it may rear-end it before it stops in the stop block. There are also considerations of what happens when either train has lighted cars with two pickups, that will bridge the gap after the locomotive has departed the stop block.
I think that the scheme that I described in an earlier post is more robust. It keeps any following train from entering an occupied block absolutely. The only restriction on the trains' makeup is that they be shorter than the shortest block; and that applies only if the number of blocks in the loop is only one more than the number of trains running on the loop. The penalties for this are the need to isolate a complete outside rail for each block and to use a relay for each block.
I have some comments about Mike's schematic diagram:
o The electrolytic-capacitor symbol shows the positive terminal (the straight line of the symbol) connected to the negative rectifier terminal. I doubt that his boards are actually wired that way, since his capacitors have not exploded!
o There are plus signs at several points at nodes that carry AC voltage--the center rails and the two non-common transformer voltages.
o It might be better to use a double-pole disabling switch, with the two poles connecting the transformer to both center-rail sections, so that the relay doesn't interrupt power twice for an instant each time a train goes through the control block.