05 Dec 2022 - 8 min read
Controller Design: MOV8, MOV16 & MISC Instructions
Way back in 2019 I discussed how you can’t ‘half design a PCB’ and that, as a result, my controller cards already have all the required functionality laid …
20 Nov 2022 - 4 min read
Well, what a journey that’s been then … I started work on a clock for my relay computer back in May 2020 and today (20th Nov 2022) this post marks the end of it. …
05 Nov 2022 - 3 min read
Quite a while ago I decided to give up on the tedious wire wrap technique for building my cards. Although it was certainly more authentic and in-keeping with my …
22 Dec 2019 - 4 min read
Decoder Design: Schematic & PCBs
I’ve almost got everything I need now to get my relay computer to do branching. The hard work of designing and constructing the sequencer and controller units is …
20 Dec 2019 - 4 min read
Controller Design: Schematic & PCBs
In my last couple of posts I finalised the controller schematic designs for the ALU, SETAB, MOV8 and GOTO class of instructions. Now it’s time to bring all those …
07 Dec 2019 - 3 min read
Controller Design: ALU, MOV8 & SETAB Instructions
In my last post I covered off the controller design for the GOTO instruction. Being as I’ve decided to implement the controller on a new set of PCB cards I need to …
30 Nov 2019 - 3 min read
Controller Design: GOTO Instruction
With the sequencer now designed and constructed I’m much closer to getting branching working on my relay computer. The next hurdle is updating the controller cards so …
11 Nov 2019 - 5 min read
Sequencer Design: Schematic & PCBs
I’ve got the designs for the 24-cycle FSM and pulse distribution in place so all that’s left for the sequencer is to bring the schematics together and then design …
02 Nov 2019 - 2 min read
Sequencer Design: Pulse Distribution
In my last post I extended the 8-cycle FSM (finite state machine) design all the way up to 24-cycles so that we can run longer and more complicated instructions. In this case …
01 Nov 2019 - 3 min read
Sequencer Design: 24-cycle FSM
Recently I’ve been looking at what’s needed to implement branching in my computer (the upcoming GOTO class of instructions). In my last post I covered the timing …
06 Oct 2019 - 4 min read
In my last post I covered the design for the GOTO opcode which will enable my relay computer to perform branching, loops and so on. Here’s where I got to last time: …
23 Sep 2019 - 7 min read
There’s been a common theme recently in the comments on my YouTube videos … people are ready to see my relay computer gain the power of branching and become a …
09 Aug 2019 - 9 min read
It’s time for the oddly therapeutic part of designing a PCB … laying out the board. In my last post I covered the schematic design and so we now have all the …
15 Jul 2019 - 8 min read
In my last couple of posts I’ve been building up to a change of approach in how I’m making the cards in my computer. This is mainly because I can’t face the …
14 Jan 2019 - 6 min read
In my last post I touched on how the repetitive nature of making register cards has been putting me off progressing my relay computer. If you’ve followed my blog (over …
07 Feb 2018 - 4 min read
Auxiliary Control Design (Part 3 of 3)
This is the last post in a mini-series of three covering the design of the auxiliary control unit which will ease entering and inspecting programs in the computer’s …
29 Jan 2018 - 12 min read
Auxiliary Control Design (Part 2 of 3)
In my last post I made a start on the auxiliary control design which once completed will make it much easier to load instructions in to memory - effectively it’s a …
24 Jan 2018 - 6 min read
Auxiliary Control Design (Part 1 of 3)
My relay computer is now at the point where it can execute a program in memory without assistance. In order to do that though, of course, the program needs to be loaded into …
17 Sep 2017 - 5 min read
Control Design: Fetch and Increment
The design of the computer’s memory, incrementer and program counter are now complete but there’s one last piece of the ‘puzzle’ required to get the …
06 Sep 2017 - 6 min read
In my last post I started the design for the computer’s memory unit which is spread over two cards. With the lower memory card design in place its now time to finish the …
03 Sep 2017 - 8 min read
In my last post I explained my decision to use a ‘modern’ memory chip in my relay computer … I also alluded to there being some complexities in interfacing …
17 Jul 2017 - 3 min read
In my last post I covered the design of the 16-bit half adder which takes whatever value is currently on the address bus and increments it by one. To make this incremented …
15 Jul 2017 - 2 min read
Incrementer Design: 16-bit Half Adder
In the last post I introduced the design for the 1-bit Half Adder. This post covers connecting sixteen of these units together to make the 16-bit Half Adder. So, diving …
04 Jun 2017 - 3 min read
Incrementer Design: 1-bit Half Adder
Typical isn’t it?! … you wait 10 months for a post and then two come along at once. Well, all being well, this should be the first of a short flurry of posts as I …
29 May 2017 - 6 min read
Register Design: Program Counter
It’s been a while since my last post … pretty much 10 months in fact … and I’d love to say I’ve been quietly working on my relay computer in …
08 Apr 2015 - 4 min read
User Interface Design: Instruction, Clock and Sequencer
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. The final …
04 Apr 2015 - 6 min read
Control Design: MOV-8, ALU and SETAB (part 2 of 2)
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. With these in hand I can now move on to …
31 Mar 2015 - 9 min read
Control Design: MOV-8, ALU and SETAB (part 1 of 2)
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 …
22 Mar 2015 - 6 min read
Pulse Distribution Design: Pulses C,D and E
In my last post I covered the design of the 8-cycle finite state machine (FSM). In this post I’ll now take the outputs from that FSM and combine them to produce the …
26 Jan 2015 - 6 min read
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 …
04 Jan 2015 - 5 min read
Decoder Design: MOV-8, ALU & SETAB
In my last post I introduced the design for the instruction register which holds the current 8-bit opcode that the computer is executing. The next card to design is the …
01 Dec 2014 - 6 min read
Register Design: Instruction Register
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 …
19 Sep 2014 - 11 min read
Sequencing & Control Design: Overview
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. …
20 Jul 2014 - 5 min read
User Interface: Display B Initial Design and Construction
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. This time I’m turning my …
12 Jul 2014 - 5 min read
User Interface: Display A Initial Design and Construction
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 …
05 Jul 2014 - 6 min read
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 …
11 May 2014 - 6 min read
Register Design: B and C 8-bit Registers
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 …
24 Apr 2014 - 5 min read
Register Design: Dual Output 8-bit Register
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). I’m now making a start on the …
20 Apr 2014 - 5 min read
Register Design: A and D 8-bit Registers
In the last post I introduced the design for a general purpose 8-bit register. This post covers taking two of those registers along with status LEDs and gating relays to …
16 Apr 2014 - 4 min read
Register Design: 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. This permits …
10 Apr 2014 - 5 min read
Enclosure Update: Laser Cutting
I couldn’t resist it any longer … I’ve ordered the laser cut parts for the case doors, sides and bay floor/ceilings. I did say I’d wait for my chosen …
01 Mar 2014 - 4 min read
Sorry, I will try to rain in the terrible punning post titles. This time I wanted to share the thoughts and ideas I’ve been having around building a case to hold my …
04 Feb 2014 - 2 min read
I’m taking a break … just a short one. In between all the bouts of wire wrapping for the ALU arithmetic card I’m starting to think about enclosure options …
03 Dec 2013 - 4 min read
Backplane Design and Construction
Originally when I was thinking about how I’d connect up the various cards of this computer I had ribbon cables in mind. Ribbon cables are straightforward to use and …
01 Dec 2013 - 4 min read
In the last three posts I introduced the design for the 3-to-8 Function Decoder, Zero Detect circuit and the Condition Registers. In this post I’ll put all three of …
30 Nov 2013 - 4 min read
ALU Design: Condition Registers
This post covers the design of the ALU Condition Registers which along with the 3-to-8 Function Decoder and Zero Detect circuit (both covered in my previous posts) make up the …
23 Nov 2013 - 2 min read
This post covers the design of the Zero Detect circuit which along with the 3-to-8 Function Decoder (covered in my last post) and the Condition Registers (next post) make up …
20 Nov 2013 - 2 min read
This post covers the design of a 3-to-8 Function Decoder which along with the Zero Detect circuit and Condition Registers will all go in to the ALU Control Card. The Decoder …
17 Nov 2013 - 5 min read
ALU Design: 8-bit Arithmetic Unit
In the last post I introduced the design for the 1-bit Arithmetic Unit. This post covers connecting eight of these units together to make an 8-bit Arithmetic Unit along with …
15 Nov 2013 - 3 min read
ALU Design: 1-bit Arithmetic Unit
This post covers the design of a 1-bit Arithmetic Unit that can add two input bits together (B and C) with carry in and out. Here’s a schematic of the 1-bit Arithmetic …
13 Nov 2013 - 5 min read
In the last post I introduced the design for a 1-bit Logic Unit. This post covers the design effort to cram 8 of these on to a single pad board complete with connectors, …
11 Nov 2013 - 5 min read
This post covers the design of a 1-bit Logic Unit that can produce AND, OR, XOR, NOT and SHL (Shift Left) outputs from two input bits B and C. Here’s a schematic of the …
10 Nov 2013 - 6 min read
If there’s one thing a relay computer needs a lot of it’s … erm … relays (of course) … which happens to be a bit unfortunate as relays, …