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Old 6th Jun 2020, 11:31 am   #541
Timbucus
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
Those look like standard D6 switches with custom keycaps. Later models of MK14 had provision for D6 switches didn't they?
Yes the Martin board is an exact copy of the Issue V so can have domes or those switches. I have gone for domes as I want a close replica.
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Old 6th Jun 2020, 11:36 am   #542
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
Those look like standard D6 switches with custom keycaps. Later models of MK14 had provision for D6 switches didn't they?
Indeed they did. I have a full set of D6 switches in appropriate groups of colours (images earlier in the thread) but no holes for them to go into. Holes for 'proper' switches on original SOC PCBs didn't appear until issue IV onwards.
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Old 6th Jun 2020, 12:15 pm   #543
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Default Re: MK14 schematic revisions

I think there will be an issue 1.3 of my board sometime in the future (but don't hold your breath waiting!) Because I want to correct the dimensions and position of holes, find a keypad solution that works (or at least allow the JM one to be fitted), bring NENOUT to the edge connector, correct the silkscreen etc. Providing support for a multi page extension.looks tricky without adding more chips or completely redesigning the address decoding to use 74138 type chips. An alternative is to make a piggy-back board that sits on top that's connected by wires and includes the extra circuitry in a manner an enthusiast would have in the 80s. I'm warming to that idea considering multi page is an option that would appeal to relatively few people.
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Old 6th Jun 2020, 12:17 pm   #544
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Default Re: MK14 schematic revisions

yes I have so many projects in progress I think you’ll get there before me
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Old 6th Jun 2020, 1:03 pm   #545
Timbucus
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
I think there will be an issue 1.3 of my board sometime in the future (but don't hold your breath waiting!) Because I want to correct the dimensions and position of holes, find a keypad solution that works (or at least allow the JM one to be fitted), bring NENOUT to the edge connector, correct the silkscreen etc. Providing support for a multi page extension.looks tricky without adding more chips or completely redesigning the address decoding to use 74138 type chips. An alternative is to make a piggy-back board that sits on top that's connected by wires and includes the extra circuitry in a manner an enthusiast would have in the 80s. I'm warming to that idea considering multi page is an option that would appeal to relatively few people.
I think the Multipage would involve removing chips from the board and leaving the sockets empty - after all that is what we would have done as well BITD so don't dismiss that option. I was thinking the RAM board could have space for an 8K EPROM (NIBL and SCIOS would easily fit) as you can still get them cheaply and easily and the modern TL866I+ can program the 12v versions at least... BASIC /RAM board is an all in one then...

It feels fairly retro for an early 80's addon... as the bigger static RAMS were becoming available etc.
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Old 6th Jun 2020, 1:33 pm   #546
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Default Re: MK14 schematic revisions

The design likely given by SoC (as there is a comment somewhere I can't remember - write for details) for the 1.5K by the way was:-

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(from the Williamson and Dale "Understanding Microprocessors with the Mk14")

The article in PCW April 1980 (Called Beefing up the MK.14) creates an offboard paged RAM system by using a 40Pin header and moving the SC/MP to the expansion board... effectively buffering the base unit onto Page 0... and accessing the board using some of the address holes - that was the way I was thinking of going for my NIBL addon. It would work with any of my MK14's then. I cannot post the article as I have a copyright reprint from the Museum. - here is a snippet which probably counts under fair use...

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Old 6th Jun 2020, 1:36 pm   #547
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Default Re: MK14 schematic revisions

The obvious way to do it is to make a board that has the SC/MP on and plugs into the processor socket, allowing any signals to be intercepted with only a few wires required to connect to the edge connector for the extra address lines. The Elektor computer puts the 4k NIBL EPROM on page 1 so I could include a ROM on page 1, and 32k RAM socket and RS232 driver for a complete solution with minimal board modifications. It would also have the advantage of working on any MK14 and many other SCMP based machines.
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Old 6th Jun 2020, 1:41 pm   #548
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Default Re: MK14 schematic revisions

Oh looks like we crossed posts!
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Old 6th Jun 2020, 2:04 pm   #549
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Default Re: MK14 schematic revisions

Reading the PCW article I can see why they remap to an address hole, because the MK14 doesn't always gate the device selects with NRDS/NWDS as they should, so selecting a non-existent address makes sense. Where that address is I'm not sure - presumably somewhere in the display or keyboard areas.
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Old 6th Jun 2020, 2:48 pm   #550
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Default Re: MK14 schematic revisions

No they use a portion of the 1.5K hole created on the Issue 5 - they do discuss modifying the INS chip areas as well but, that leads to issues as some software uses the shadows for various reasons.

My view would be that you would either use the simple expansion memory we plug into the expansion board used to hook up the VDU, Tape Interface, Provide headers for the INS8054 etc OR you use the offboard NIBL >4K memory system and it uses the hole we have already created or can be created on older boards with the mods given by SoC:

Extra notes with Issue 4: Click image for larger version

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Not sure where these are from but, it is for earlier boards: Click image for larger version

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Don't forget that the BASIC module in development by SoC used the new bigger 40 key keyboard which plugged on the edge connector so I would look to develop that and modify the Elektor Page1 NIBL to use it for input (and the VDU for output) rather than needing to use the Serial I/O although no reason both could not be supported.
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Old 6th Jun 2020, 3:48 pm   #551
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Default Re: MK14 schematic revisions

This is starting to get a bit (feature) creepy...
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Old 6th Jun 2020, 4:17 pm   #552
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Default Re: MK14 schematic revisions

Yup but, it is my ultimate goal to get to what 'could have been' in the SoC lab before they abandoned it and ran off to develop the Acorn 1 because allegedly Clive was not really interested in developing a BASIC computer.

It is all modular so people can use what they want - we will still want the simple 1.5K expansion that either fits between the board and the VDU or can sit on the long thin expansion / U bend backplane.

The NIBL board on top of the CPU will just mean you do not need the 1.5K expansion.

If you really want to get creepy the NIBL board should have space for stacking upto four SC/MP in a multiprocessor arrangement... like this one from Mark Pepper:

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Old 6th Jun 2020, 5:10 pm   #553
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Default Re: MK14 schematic revisions

OK, some comments on the original keyboard parts.

The metal sheet is coated (mild) steel. It's magnetic.

The dimensions are as follows (Letters in brackets refer to the sketch in an earlier post):

The hole for each key : Width (C) = 12.6mm, Height (D) = 10mm. The corners are radiused at about 2.4mm

Horizontal measurement for the whole plate :
------------

Overall width : 89.2mm

Fixing hole spacing (A) = 79.4mm

The 'dividers' between the keys (both from edge to first hole and between the holes) (E) = 7.7mm

As any metalworker knows, adding up dimensions generates small errors. So I measure the distance from the left hand edge of the plate to the left edge of each hole and got
7.7mm, 28mm, 48.4mm, 79.4m

----

Vertical measurements for the whole plate :
-----
Overall height = 92.6mm
Distance from edge to nearest edge of a key hole ('edge divider') = 10.1mm

Fixing hole spacing (B) = 81mm

Internal dividers (F) = 5.2mm

As before I measured the 5 distances of the bottom edges of the holes from the bottom edge of the plate to avoid accumulating errors : 10.2mm, 25.4mm, 40.7mm, 56mm, 71.3mm

The fixing holes are about 3.7mm diameter.

As for the overall construction of the keyboard :

The first version used conductive rubber. There were 4 parts to the keyboard :

A plastic sheet with a circular hole for each key that was stuck to the PCB
A rectangle of conductive rubber
A legend sheet (thin plastic)
The metal frame.

These were supposed to be held to the PCB by plastic clip pegs through the corner holes. Almost everybody (including me) used nuts and bolts... Note there were no buttons, you pressed on the legend sheet to push the conductive rubber against the PCB.


The second version was the metal dome switches with plastic buttons.

There was the same sheet-with-holes stuck to the PCB.
A metal contact dome went into each hole
Then a double-sided self-adhesive sheet on top of the dome.
Then the (same) legend sheet
Then the buttons through the holes in the (same) metal plate.
Again fixed together by plastic clips or nuts and bolts.

I have made high(ish) resolution scan of the metal plate and legend sheet. Too large (12MBytes or so) to post here, but I can send it to anyone who needs it, e.g.if you want to copy the original font from the legends.
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Old 7th Jun 2020, 10:06 am   #554
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Default Re: MK14 schematic revisions

Thanks for the very comprehensive measurements and information Tony. I would certainly appreciate it if if you would email me the scan of the key legend sheet, because at some point I will need to legend the key switches of the 'new' PCB. I'm not sure if my email provider can cope with such large files, just have to try it and see?

Tim, if you find the key caps in white rather than green, please let me know as I have not (yet) ordered any of the green ones.
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Old 7th Jun 2020, 10:32 am   #555
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Default Re: MK14 schematic revisions

I've looked about everywhere I can think of and those green switches are the only type I can find for sale at the moment with the clear covers. Perhaps a can of plastic primer?
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Old 7th Jun 2020, 11:51 am   #556
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Default Re: MK14 schematic revisions

Well I suppose I could have predicted as soon as I posted the above I would find a source of switches. I searched for "A14 clear keycaps" on a famous auction site and found these:
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Presumably those search terms or similar should work on other sites too. It would be nice to find an actual distributor like Farnell or Rapid that stocked them.
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Old 7th Jun 2020, 12:24 pm   #557
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Default Re: MK14 schematic revisions

The first site which came up sells a fantastic range of switches and caps but unfortunately the switches are quite expensive and there doesn't appear to be any discount for 'bulk' so a set of switches with black square tops, not including clear covers, would cost ~£50. Probably still worth buying the green ones from the source you originally linked and trying to find the A14 caps separately.

They seem to have a nice low profile, those A14 switches, what do they actually feel like?

Remember the 'Schadow Digitast' keyswitches so beloved by Elektor that they used them on practically everything? The ones with the keytop hinged at one end? I discovered the other day that C&K still make them, or something very like them, also called 'Digitast'. Of course they don't fit in the footprint of these PCBs.
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Old 7th Jun 2020, 1:07 pm   #558
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Default Re: MK14 schematic revisions

I've just bitten the bullet and ordered a set of the ones Slothie linked to in #327 of this thread. I agree the green doesn't sit too well with the Gothic black of the PCB, it makes it look more Ghost Train than Gormenghast.

You may have noticed I even went for a black reset switch, even though I had an authentic red one available - but needs must. I can always learn how to wield a paintbrush again, if necessary.
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Old 7th Jun 2020, 3:09 pm   #559
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Default Re: MK14 schematic revisions

Here's a diagram showing the key coordinates in mm for the original keyboard. Measurements are as per Tony's post #533 - one measurement for the rightmost horizontal button was wrong but I've made a calculated position for it.
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Old 7th Jun 2020, 4:51 pm   #560
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Default Re: MK14 schematic revisions

Yes, sorry... The postition of the left edge of the 4th column was measured as 68.7mm from the left edge of the plate (as you calculated it).
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