Acorn Electron retrobrite and USB keyboard conversion

[GeX]

I bought a broken Acorn Electron with the intention of fixing it (look a bit like faulty RAM on the listing). So to bits it came;



It turned out though that the ULA socket on the motherboard was damaged, sourcing a new socket was expensive and I wasn't confident I could replace it without damaging the board. So plan b was formed.



Turn it into a USB keyboard in a non-destructive way, so that it can be repaired by someone else in the future if they want.

First of all though, it needed the plastics sorting out as it had gone rather yellow. Tricky to photograph as the white balance on the camera kept correcting for it!

The top case with white paper underneath got it.



Time for some masking and BBlonde peroxide;




Wrapped it in cling film to stop it drying out and left it out in the sun



Comparing it to the base after one treatment



Certainly better but nowhere near good enough. Repeat and do the keys too;



Next up I did the lower case, and keys again. No more photos of that.

With that out the way, onto the bits of USB keyboard mode. Kits exist off the shelf for doing this but I wanted to roll my own. FRDM-KL25Z

Potato photo of the board being tested



The board and wiring were suggested by https://www.instructables.com/id/Acorn-Electron-USB-keyboard/ I modified the software slightly to change the key mappings and opted not to remove the stock keyboard connector (as no destruction please) and instead used dupont cables with pins in the headers to allow me to join it all up.

Video of testing it

After testing, I found a few dead keys. Some of them began working after squirting contact / switch cleaner in and actuating them a few times. One or two required a poke with the soldering iron to reflow the joints.



Route the wire out of the case. I did buy a surface mountable socket for it, but could not work out how to securely mount it without drilling holes in the case.



And the end result;



Quite pleased with it; I had great fun building it but I don't have it anymore as I posted to a good friend of mine as a surprise as his first computer was an Acorn Electron

 

[sideways14a]

Those ULS were always such a big deal, wasnt there many problems with the 'leccys ula in its time?
My first real computer as well.

 

[pingwing]

That is exceedingly cool!

 

[Rroff]

It turned out though that the ULA socket on the motherboard was damaged, sourcing a new socket was expensive and I wasn't confident I could replace it without damaging the board. So plan b was formed.

Not so much the sockets like that but I knew someone who was able to replace many of the ICs on those old Acorn/BBC systems with pin compatible breakout boards using modern discretes and ICs - I have no idea where he had the knowledge from for figuring the functionality of the original chips out and how to replicate them. Sadly passed on a few years back as there are a few people who'd love to have that ability to bring some of those old systems to life again.

Pretty cool little project.

 

[GeX]

Not so much the sockets like that but I knew someone who was able to replace many of the ICs on those old Acorn/BBC systems with pin compatible breakout boards using modern discretes and ICs - I have no idea where he had the knowledge from for figuring the functionality of the original chips out and how to replicate them. Sadly passed on a few years back as there are a few people who'd love to have that ability to bring some of those old systems to life again.

Pretty cool little project.

Most of the chips in 8bit machines of this era are off the shelf parts. A lot have been improved in time and can be replaced with more modern parts (memory in particular). It is the ULA that makes the machine what it is.

A ULA is an Uncommitted Logic Array. It contains a number of general purpose cells with no connections between them. To customise the ULA, the chip designer creates a wire mask that interconnects the various cells in the way that is needed.

This is the ULA from the Electron




For the ZX Spectrum Chris Smith reverse engineered the ULA and wrote a book about it; http://www.zxdesign.info/book/ It's very good for anyone interested in computers of this era.

Here is the Spectrum ULA reimplemented on breadboard https://www.flickr.com/photos/37778900@N06/4843185181

It is on the back of Chris' work that means we have FPGA based replacements for the ULA and projects like https://www.specnext.com/

 

[jsmoke]

I had an electron years ago. Not a bad machine.

 

[Rroff]

Most of the chips in 8bit machines of this era are off the shelf parts

Some models of the BBC, etc. have chips not so readily available - I've no idea if he tried doing anything with ULA, etc. I remember back in the day he was salvaging some BBCs from one school to use at another and he was there with a huge sheet of graph paper working out one of the chips to make up a board - I assume he had access to equipment to do decapsulation and scanning, etc. or something - no idea where he had the knowledge from as to the internal workings.

 

[GeX]

Some models of the BBC, etc. have chips not so readily available - I've no idea if he tried doing anything with ULA, etc. I remember back in the day he was salvaging some BBCs from one school to use at another and he was there with a huge sheet of graph paper working out one of the chips to make up a board - I assume he had access to equipment to do decapsulation and scanning, etc. or something - no idea where he had the knowledge from as to the internal workings.

Yes, my mistake some of the BBCs do have some more obscure chips. It's good to hear that people like that had been working to reverse engineer them for some time, there's a community around them now and things like https://github.com/hoglet67/PiTubeDirect/wiki exist.

 

[Rroff]

Yeah sadly he passed away a few years back - his knowledge would have been really useful to some of those communities. I've seen a few requests over recent years for information on some of those chips and/or trying to salvage them from old machines people have.