User Interface: Display B Initial Design and Construction
Whereas display A is dual purpose allowing a user to view and initiate control signals the second display card is read-only and displays the primary state of the computer. Initially this 'primary state' comprises of the data bus contents, condition register status and ALU function code / operation. I also had a rectangular gap spare on the card that looked like it'd fit an ammeter so that also now forms part of the second display too.
As with the display A buttons and the primary input switches I've known what kind of display elements I wanted to use right from the beginning. Taking inspiration from a visit to the National Museum of Computing in the UK I fell for the big chunky buttons/indicators on the ICL 2966's 'washing machines' / storage units. Here's an example of my interpretation of that retro look:
With the selection of display units in hand I'm now able to design the display card itself. As with display card A I'm only sharing a partial design for this card ... effectively as much as I'll actually be constructing. Eventually the gaps on this card will be filled by yet more indicators for the various bits of the computer I'll add in the future. This is more about constructing the bits I need when I need them and saving money on parts until I'm ready for them rather than teasing my audience (if anyone really, really would like to see the complete design for any of these partial cards drop me a line in the comments and I'll be happy to share). Anyho, here is the design with indicator faces shown:
As always these schematics are available on my Google Docs here for the schematic with indicator faces and here for the schematic without.
So with the design all done I can move on to making the card for real. Technique wise there's nothing really new compared to constructing display card A although I have put in some DIL sockets to carry the display units just in case I ever need to replace them or tweak anything. To fit the ammeter I made a paper template first and then marked out the area on the card / pad board and drilled some pilot holes. From there I attempted to cut out the hole with a junior hacksaw but didn't get very far so I resorted to nibbling away at the board with a pair of pliers which actually worked very well. Here's the card as it currently stands from the front: