Been off line for a few days, came back to laying out the bread-board circuit, that worked for the 18-1 signals, into strip-board.
After 7 re-iterations, here it is:
I keep spotting an error, going back, making corrections, make new errors! Any 'de-bugging eyes' would be very welcome on this, I've spent several hours now, and I am now going cross-eyed over it!
Columns 2 to 8 contain the feedback amp, with Doug's values in but the feedback resistors modded to suit the pnp I have in my bin and give a high input value, which seems to work well for the 18-1.
I've added some 'earth' lines vertically between an upper and lower 0V rail. They separate each 'stage', just to help minimise feedback, FWIW, first one being between column 8 and 9.
The regulator (note, I will be using a LM2931 here, because I found the 7805 sucks up 4mA doing nothing at all, and the whole circuit takes under 2mA) and the comparator stage then go from column 9 to 18, with another 0V line running at the end of that.
The HEF40106 Schmitt trigger is to clean the signal up, as I have put in an 'anti-bounce cap' (in column 19) so the signal then needs 'cleaning'.
I also tested the HEF40106 to see whether it used less power idling with its unused inputs held high or low, or floating. I concluded they should be held high.
I've yet to deal with putting in the trimmer thresholding resistor (column 12) which will need another column or two to make it fit the holes, but otherwise I think I've made the most of the board space!! I've doubled-up on some of the holes to save a little space.