Orwell computer case.

April 25th, 2015

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Since no one reads this stuff here is a film 🙂

Over the last month or so I finally got around to making a housing for my Orwell computer. After a little distraction trying to get a SID chip working (I didn’t) I decided the hardware is finally done so it’s time to build a case. This is how I did it.

The case is custom made from steel with timber ends. First though I made up a cardboard mockup and from that started marking out steel sheet.

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The steel is 1mm on the base and 0.8mm for the top. It is in two pieces that gets screwed together with 3mm screws.

The case itself is simple sheet metal work. Lots of marking out then bending and folding and hammering around whatever bits of whatever you have hand you can bash steel around!

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I know these days it’s all about 3D printing and plastic. Bleargh! I prefer the hand crafted approach and metal and wood. I used the same approach for my Enigma watch and that came out great.

A bit of work later and you get a top. Yes I am using the back of my vintage car as extra workspace. It’s flat and it’s there!

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The base is a simple steel tray. I joggled the front and back of the top so it neatly slides into the base. To hold the timber sides on I made some side plates, also joggled so they fit flush, that I soldered to the top. They not only provide a way to screw the sides on, they stiffen the entire top.

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After making the top and soldering the sides in place I started cutting the openings I needed. The back opening for the connector panel was easy as was the slot for the front panel. The keyboard opening was a bit trickier. To do this I photographed the keyboard from above, printed it out 1:1 scale onto cardboard then cut it out. I used that as a template for cutting the hole.

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I roughly cut the hole with an angle grinder then nibbled out the rest with a hand nibbler. Final finishing was with a flat bastard (that’s a file – found that amusing when I was 10, still do now).

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To hold the keyboard in place I did use some plastic! But this is just some blocks cut from plastic chopping board. It holds the keyboard at the right angle but I deliberately made them low so I could then use washers as shims under the keyboard to get it to exactly the height I wanted. The wooden sides are attached to the top which then fits onto the base. To attach the top to the base I made up some little brackets that are drilled and tapped for 3mm screws and then soldered to the top of the case. My aim was to have no screws visible from the front or top of the machine. All the screws are underneath or on the back of the machine.I made some temporary sides from some plywood to get a template of the shape I wanted.

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The timber for the sides is oak recycled from an old dresser a friend got for me off the side of the road (we had an inorganic collection – so much great stuff people throw out). It wasn’t worth restoring so I broke it all apart for the timber.  Good timber is hard to find these days so recycling old stuff is the way to go like I did on my railway dining table.

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I’ll use other bits of that dresser on my car I am sure. I love oak. It’s seems a good, old, English timber to me. I know it comes from elsewhere too but it has that old fashionedness about it I like.

The front panel and rear panel are made from aluminium. These were drilled and cut out and painted dark green. The front panel is held to the case from inside by screws into threaded inserts soldered to the inside of the case so no external screws are needed. Those paying attention will see the serial port is the wrong sex! It was the only spare connector I had till I could get some more.

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Before fitting the sides thought the case I had to paint the case. Again inspired by the Enigma machine (I love those things!) I used crackle black paint. This stuff can be tricky to work with. The best thing is to get on a good, heavy coat (put on with lots of passes with no runs) then just leave the thing in bright, hot sunlight and let it do it’s thing. It will look like it’s gone all wrong at the start but if you just leave it things should come right. I actually didn’t do quite heavy enough coats so if you get the light just right you can see my spray pattern but the final finish was good enough to go with. The inside I painted with zinc rich weld though primer so it won’t rust.

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After it’s dried I also bake it in the oven at about 100c for an hour or so. You eventually end up with a nice, hard, textured finish. The real Turing/Welchman bomb at Bletchley has the same finish actually (although I wonder if it’s painted or powder coated though?). I was so annoyed the one film that didn’t come out when I was there was the one of the Bombe.

After the paint dried I could assemble thing. First I had to make sure the main computer mounting was correct. This is the aluminum chassis the main Orwell board and the IO board were attached to. I did experiment with a SID sound board but in the end abandoned it when I couldn’t get it to work right. Orwell wasn’t designed to take one so I never got it to work right. I think the issue was the addressing/chip select. You can see the SID board here though. It’s the bottom most board.

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The main chassis is just attached to the base of the case with 3mm screws and nuts. It’s a bit hard to see but on the left hand side of the main chassis are the voltage regulators and the amplifier module.

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The front and rear panels were painted a very dark green and I etched and painted up a custom brass logo for the front of the machine.

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The D sockets on the back are a serial port, an analogue joystick port and a general purpose IO port.

There is a speaker driver by an internal amplifier. The volume control is on the front panel. We also have an external audio output as well as composite out and a power supply  for the LCD screen. This screen is a 7 inch car monitor from DealExtreme. It works very well and also has a VGA input in case I ever upgrade Orwell.

A few software changes to mention (I am sure no one reads this stuff). I tweaked my loading routines. Running the serial port flat out was causing the machine to go mental. It would just lose it’s brains. At first I thought it was because the serial port was overloading somehow but in the end I figured what was might be happening was that I was trying to ram characters into the parser too quickly and ended up sending it rubbish it couldn’t parse correctly. to test this theory I ended up using the flow control and stopping the serial port when a full line was received and then starting it again after the line was parsed. This seems to have fixed the issue.

I also added a binary load mode. This lets me load data directly into memory at a given location. This is handy for uploading machine code routines (which is so painful via BASIC) or other binary data. With the new screen working well I also set the default width back to 80 columns too.

 

10 Responses to “Orwell computer case.”

  1. Rich Says:

    Some people read it

  2. Simon Says:

    As long as there is someone I will keep doing it then 🙂

  3. Alan Says:

    Hi Simon,

    First off this is a remarkable project, very impressive.

    I was wondering if you would be willing to assist me with a problem I am having. I am attempting to connect an old oric keyboard to usb using an arduino board. I am unsure of how to wire this and don’t understand the oric keyboard schematic. You seem a good person to ask as you have used the same chip set. Please treat me as a complete layperson or ‘noob’ as they say these days. I will of course elaborate if you are willing to help me.

    Thanks in advance,

    Alan.

  4. Simon Says:

    I’ll email you!

  5. Michael Says:

    Hey! I love your blog! Don’t fall in to the “no one reads this” trap please 🙂

    Maybe start a Patreon? I’d contribute now and then.

  6. Simon Says:

    I’ll still update it if no one reads it. Half the time it functions as my documentation so I can remember how I did things.

    Should be doing an update on Orwell and the Turing Bombe very soon.

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  10. Martin_H Says:

    Have you posted the assembly source for your computer? I’d love to read through your keyboard scanning code for some ideas. TI 99/4a’s can be bought cheaply and I could get the keyboard and the tms9918a and RAM chips to add to my computer.