Two nights ago, I was sat scribbling in my notebook when my wife came to see what I was doing. She took one look at the product of my pencil, gave a disappointed sigh and declared "I don't want to know. I'm going to bed." and left me to my muttering accompanied sketches...

I mentioned back when I was trying out a Viessmann signal that I was considering designing a solid state interlocking panel for point/signal control. The idea just won't go away. I can't quite settle for individually controlled points and signals, I just wouldn't feel I'd done a good job unless they corresponded to one another. PC control is a possibility, but it doesn't seem right to control semaphores with the click of a mouse. I also had a go with Modratec's SigScribe, but had difficulties when it came to the group exit signal. A great shame, as I would love a physical interlocking frame. Doubtless a bit of trickery could fool SigsScribe into fitting my requirements, but solid state components are a lot cheaper. Don't be mistaken, I don't think Modratec frames expensive, it's just that I'd rather spend such money on a longer term layout.

So back to the muttering and scribbling. I won't pretend that I honestly know what I'm doing. My limited electronics tuition from my schooldays seems a long time ago, so I'm working from first principles. This may sound funny, but at this point I'm not after help with it- I'm going to try it in Crocodile Clips before actually building anything. I've also only drawn one side of the circuit, and only the control parts, not the actual power to the points and signals (which will be with relays or transistors). Ignore all the numbers scrawled on, they're just the results of me thinking with graphite.

As I look at the diagram again, I find myself questioning aspects, and wondering how far the interlocking should go. For instance, is it enough to have in one instance a conflicting route simply setting anything crossing its path to stop aspects, or should I make it that the route cannot be set other set routes conflict? The prototypical answer is the latter, but is that just making extra work for myself? I also look at the digram and wonder why I have done certain things. I think that a whole fresh draft now I've got the general ideas in my head may be worthwhile.