A blog about a computer made from relays on Relay Computer

It’s been a bit quiet on the relay computer front again for a while … well it is summer after all and there’s no point staying inside the house tending to my hobbies when I can be running around outside getting sunburnt.

It’s finally time to give all the cards created so far a test so I can check everything works together as expected.

Before I can test the new decoder, sequencer and controller cards all working together with the rest of the computer I need to construct the ‘W’ backplane which the new cards sit on.

Well, the good news is I’ve just passed a major milestone in constructing this relay computer … it can now perform a single instruction in full firing the various control lines as needed.

So yea, it’s been a while since my last post … in fact it’s been just over six months.

I’m just about at the half way mark now for getting the computer to operate the MOV8, ALU and SETAB instructions.

In a change from prior form I’m combining the construction and testing of the next card in to a single post this time.

Following on from my last post, and after popping in some relays, the instruction register is complete and looks like this: As usual I’ve put a video together that demonstrates this card in operation.

There’s been lots of theory going on in my recent posts but the time for design is over (for now) … it’s time to get constructing.

Those who have been reading my posts and watching my videos (you have my sympathy) will know that alongside constructing this computer I’ve also been busy renovating a house I bought almost a year ago.

Over my last seven posts I’ve been slowly putting together the card designs so that the computer will be able to operate the MOV-8, ALU and SETAB instructions.

In part one of this two part post I introduced the design of the control relays for each of the MOV-8, ALU and SETAB instructions.

Over the last five posts I’ve been building up the design of a set of cards so that the computer will be able to understand and perform the MOV-8, ALU and SETAB instructions.

In my last post I covered the design of the 8-cycle finite state machine (FSM).

So far I’ve got the design complete for the instruction register along with the initial design for the decoder and so I’m well on the way to having the computer perform MOV-8, ALU and SETAB instructions.

In my last post I introduced the design for the instruction register which holds the current 8-bit opcode that the computer is executing.

Well, it’s fair to say that I rather underestimated just how much time decorating the new house would take up … and that’s mainly because ‘decorating’ included re-wiring, re-plumbing, re-plastering, re-carpeting … all before I got anywhere near choosing a…

I’ve now got my computer to a state where I can perform ALU operations and push values around the four registers by manually operating the various control lines.

Now that the two display cards are complete enough to display and control the status of the ALU and four registers (A-D) it’s time to fit them to the upper enclosure.

In my last post I put together the beginnings of the first display card … named in a brilliant flash of nomenclature as display card A.

Following on from working on the main data switches in my last post this time I’ve taken the first steps in designing and constructing the first of two display cards which will sit in the upper enclosure.

Now I’ve got a fully working ALU and four registers completed I want to take a short break from card building and turn my attention to making it easier to interact with the computer.

The A/D Register card is now complete and looks like this: As usual I’ve put a video together that demonstrates this card in operation.

I haven’t posted in nearly a month but in between bouts of enjoying the rare British sunshine I’ve been plodding away at the A/D register card and it’s now finally ready for testing.

The B/C Register card is now complete and looks like this: As usual I’ve put a video together which demonstrates this card in operation … firstly on its own but then together with all the other cards constructed so far.

As mentioned in my last post I decided this time around not to post after each stage of card construction (being as the construction steps are now pretty similar to those for previous cards).

In a recent post I put up the design for the A and D 8-bit register card … the B and C register card is very similar in design but has the additional complexity that it has to directly feed the ALU.

Just need to quickly share my experience with what I’m dubbing the ‘magic pen’ before I put up the B/C register schematics (yup, they’re finally ready).

I was going to spread the fitting of the laser cut parts to the lower enclosure over a couple of evenings but in a fit of geeky excitement I ended up doing it all in one evening.

I’ve been looking forward to this moment for nearly a month … the laser cut parts I ordered to move my enclosure construction forward have finally arrived.

In the last post I introduced the design for the A/D register card (which as its name suggests contains the A and D 8-bit registers).

In the last post I introduced the design for a general purpose 8-bit register.

This post covers the design of a general purpose 8-bit register that can be loaded from the data bus and then selected back to the data bus at a later time.

I couldn’t resist it any longer … I’ve ordered the laser cut parts for the case doors, sides and bay floor/ceilings.

Following my last post on the completed backplane I’m now in a position to connect all the other completed cards together to test the full ALU.

In my last post I mentioned I’d suffered a bit of a set back with the construction of the ALU backplane.

I’ve been promising this post for quite a while now … an update on how the enclosure construction is going.

The ALU Control Card is now complete and looks like this: This card was, on the whole, much simpler and quicker to put together than previous cards (despite me initially messing up the zero detection relay positions).

I’ve been a bit short of time lately so I’ve been working on the ALU Control Card in little bursts … but after lots of these little bursts I’ve now got all the power rails and wire wrap done for this card.

Following on from the first two successfully completed ALU cards, for logic and arithmetic, it’s time to make a start on the control card (well, actually, the LEDs and connectors are already done from earlier but you get the gist).

Sorry, I will try to rain in the terrible punning post titles.

The ALU arithmetic card is now complete!

I’ve managed to squeeze in a couple more wire wrapping sessions this week so in this post there’s a few photos of progress so far.

Fear not (just in case you were for some reason) all this talk of Sketchup and enclosures and so on hasn’t totally diverted me from the main task of constructing the ALU.

I’m taking a break … just a short one.

Another round of soldering done … this time putting down the power rails on the arithmetic card along with some soldered wire links.

So, as mentioned in my last post this time I’ve put in the wire links and wraps needed to test the first bit of the arithmetic card.

It’s always a fiddly job getting the relay sockets soldered in and the ALU arithmetic card proved no exception.

Following on from the successful construction of the ALU logic card in my last post it’s time to start off the new year with the next ALU card (number 2 of 3 ALU cards in total) … the arithmetic card.

The ALU logic card is now finally complete!