John, I really do think you could do it all with 3-aspect signaling. Flashing aspects are cool, as are double aspects, but they add complexity that has to be balanced against play value. And, if you mean to install bidirectional signaling (which does have play value) 3 aspects can do it quite well. Signals that simply change color are visually attractive, but they are only decorative, and not useful. The upside is that they're simple (often actuated by infrared light) but the downside is that a train could stop right after passing the signal and be sitting just beyond it when the signal timer changes the aspect from red to yellow to green. So, a train could pass a green signal and immediately run into the rear end of the preceding train. That doesn't bother some, but others want the signal to indicate that the train may safely proceed past it. You don't need an extra signal at the leaving end of a siding. In prototype ABS there is usually not one. The train leaving the siding checks the signal for the main track, then throws the switch and leaves the siding governed by the aspect that was observed.
- Green is a no-brainer. Track is unoccupied in the next block and all switches within that block are properly aligned for the main route.
- Yellow indicates that the next signal in advance will be red.
- Red indicates that the block it governs
- is occupied, or
- has one or more switches that are not properly aligned for the main route.
Prototype Automatic Block System (ABS) -- especially where semaphores were used -- did this exact thing. Rules provided that a train could pass a signal displaying Stop (red) without stopping, at Restricted Speed, if the switch was properly aligned for it to enter a siding.
To get play value from a bidirectional signal system which actually indicates track occupancy, you need four blocks at the minimum, and each signal location requires opposing signals. This can be either two separate signals, or one signal mast with opposing signal heads mounted on it. Obviously, you have to insulate the track into blocks, and you have to detect switch position, which, for a person of your electronic abilities, should be very simple. A couple of more insulated joints can create a trap circuit within a block, to activate crossing signals. Just make every trap circuit long enough to provide some advance warning in each direction.
I did put a gold-plated signal system on my layout, but it was really expensive, and -- because the railroad is not a whole-house basement size -- I actually think that I could have done it with three indications and been perfectly happy.
It's easy to get carried away on signals. It is wise to remember that they are just another operating accessory and three aspects add plenty of fun to operation of the layout without great complexity and at a reasonable cost.
