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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 17th Oct 2016, 6:35 pm   #41
SiriusHardware
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Default Re: The Sinclair / Science of Cambridge MK14

I went off on a ramble around the net and found this page, which is presumably the 'original release' version?

http://www.techlib.com/area_50/Readers/Karen/micro.htm

That will be fine just to get the hardware up and running, I can always plug in the most up to date code later. I had no trouble getting the (very tidy) source to assemble in MPLAB, once I had incorporated it into an MPLAB project and specified the processor.

Maybe you could just put the most up to date code / project info on that site at some point, so that any interested person can access it without necessarily taking up more of your spare time on a by-individual basis?
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Old 5th Jan 2017, 11:56 pm   #42
SiriusHardware
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Default Re: The Sinclair / Science of Cambridge MK14

(Very slow) work in progress on the PIC based emulator:

The 'proper' keyswitches were originally from a full QWERTY legended set which I bought at a radio rally in the mid nineties. The 0-9 numeral keys retain their original legends.

The original A-F letter keys all had a letter and some other symbol on them so I couldn't (or I chose not to) just use them as they were, scrubbed the original legends off and re-legended them with the plain letters A-F using the time honoured traditional method: Letraset transfers sealed in place with built-up layers of clear varnish dripped into the 'dimples'. The same was done for the G, M, AB and T keys.

The 'padboard' is a recycled Tandy (Radio Shack branded) late 70s / early eighties item. The switches still need to be wired up in the awkward non-conventional MK14 matrix. I will eventually drop the keypad a little deeper into the enclosure so the keys don't stick out so much - subject to there being enough room in the enclosure for the actual works if I do that.

The display (already tested with the real MK14) is from a Texet Calculator which was contemporary with the MK14.

...now, if only I could remember what I did with the rear half of this calculator-style enclosure...
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Old 22nd Jan 2017, 8:51 pm   #43
Karen O
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Default Re: The Sinclair / Science of Cambridge MK14

I've sent updated copies of my PIC14 assembler source and hex to the chap who kindly hosts my project pages, but he's a very busy man so I've attached them here
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Old 23rd Jan 2017, 12:23 am   #44
SiriusHardware
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Default Re: The Sinclair / Science of Cambridge MK14

Karen, thanks for that, appreciated.

As you've been kind enough to do all the really hard work (i.e., the design, the firmware) the physical side of the construction - lettering, sealing and wiring up the keypad and display remains the only main chore to be completed.

Once those bits are all done, wiring an actual PIC to the physical hardware should be a relatively quick job. For the 'works', I may just use one of the 44 pin PIC demo PCBs which came with some versions of the Pickit 2. They are reasonably compact and have a fair sized undedicated prototyping area with room for the display buffer / serial level shifter components, etc.
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Old 23rd Jan 2017, 1:31 am   #45
Karen O
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Default Re: The Sinclair / Science of Cambridge MK14

I've only one piece of advice: use a 74AC240 for the digit drivers. I used transistors and they didn't switch off quickly enough for some of the supplied example programs.
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Old 23rd Jan 2017, 1:36 am   #46
SiriusHardware
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Default Re: The Sinclair / Science of Cambridge MK14

Yes, I did recall that you had said that earlier so I am intending to include that modification. Thanks for the reminder though.
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Old 2nd Mar 2017, 1:39 am   #47
SiriusHardware
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Default Re: The Sinclair / Science of Cambridge MK14

Thinking about other microcontroller projects recently reminded me that I should try to make some more leaden-footed progress on this, so....

Image #1: The missing lower half of the enclosure found. If you knew what my loft looked like you'd know what a miracle this is. I only found it while I was looking for something for someone else.

Image #2: As mentioned earlier, I decided to use a PIC-friendly PCB I already had - one of the 44-pin demo boards which used to come with Pickit programmers (V2 and V3). I obtained a PIC16F877A in the appropriate package, fitted it and programmed it with Karen's updated code before adding any of the PIC14 hardware in case the extra hardware got in the way of the ICSP programming interface, although in fact I don't think it does.

I then added the 74AC240 buffer used as the display common / keypad column line driver and also the serial input level converter. The 74AC240 was probably the most awkward part to get right with inputs and outputs sprinkled evenly all the way around the device.

Image #3: (To the tune of 'Also Sprach Zarathustra'...) First time power up and MK14-reset with the display connected. This is the MK14's equivalent of 'Tadah!'

To be honest, I had powered the PCB up previously and scoped the various signal lines to see if there was the expected type of activity on the various lines and there was, but I was still expecting to find that I'd somehow mirror imaged the display, with display cell eight showing what display cell one ought to, and so on, but no, it was actually right.

Still one tedious task to go: The wiring up of the keypad switches. As anyone who knows the machine knows, the MK14's 20 keys are wired in a completely unconventional matrix, so it's not just a case of wiring each row across from left to right and each column from top to bottom. That would just be too easy.
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Old 22nd Mar 2017, 6:11 pm   #48
1980s_john
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Default Re: The Sinclair / Science of Cambridge MK14

Hi,

My mate Doug has ported an Mk14 emulator to run in a web page, written in Javascript:

http://www.dougrice.plus.com/dev/seg_mk14.htm

Enjoy!

Regards,
John
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