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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 27th Feb 2020, 8:34 pm   #261
hysteresis
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
I've just put together the attached sketch of the pinout for the MK14's display ...
...The sketch may assist with identification of suitable substitute displays...
The sketch matches the pinout of Texas Instruments TIL 393-9 and National Semiconductor NSA1198 displays (1st & 2nd attachments, respectively).

The 8-digit versions of those displays can be used as direct substitutes, as their pin order is exactly the same. My Sinclair PM200, for example, uses the 8-digit NSA1588A display. The apparent digit height of the NSA1588A is larger than that of the NSA1198 (please see attached data table), with the Texas Instruments displays sized in between.
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Old 27th Feb 2020, 9:38 pm   #262
SiriusHardware
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Default Re: MK14 schematic revisions

Thanks for taking the time to post this information, very useful. If at least two of the major optoelectronics manufacturers used it, then maybe this pinout was an established standard. I wonder how the odd / jumbled order of segment connections came about?

My MK14 is in storage so I can't check its original display just now but the display is highly likely to have been a Nat Semi part as the kits of parts for the MK14 were supplied to Science Of Cambridge by National Semiconductor.

The other 9-digit display I originally pulled from a Texet 880 calculator (and which I know works in the MK14) is a NSA1488.
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Old 27th Feb 2020, 10:24 pm   #263
SiriusHardware
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Default Re: MK14 schematic revisions

I've just been hunting around for possible alternative display donors and found this interesting site:

http://www.vintagecalculators.com/

The Texet 880 is one variation of what that site calls the 'standard type 2', a model which was sold branded with a number of different brand names. Some changed the brand name but kept the '880' model number, others went entirely their own way.

What I notice from that site is that many of the models described as '8-digit' actually have a 9-digit display with the leftmost digit not used. You can see this on many of the images where all of the displays which can be lit up are lit up, but there is an extra unlit cell on the left of the 8 lit ones.

As Hysteresis pointed out, an 8-digit display will work just as well in the MK14 if its pinout corresponds to that of digits 2-9 on the original 9-digit displays.
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Old 4th Mar 2020, 1:22 am   #264
Slothie
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Default Re: MK14 schematic revisions

Copy of post to the VDU thread:
If anyone is interested in trying my new rel 5.5 PCB which was specifically designed to connect to the VDU board by the edge connector they are at https://bitbucket.org/IanKRolfe/mk14/src/master/ and https://bitbucket.org/IanKRolfe/kica...ib/src/master/ which are bitbucket git repositories for tje boatd and the libraries i have created for components not in the default libraries. They are for an older version of Kicad (4.0.2) so if you have a more recent one you may need to fiddle with the library settings and/or ignore warnings about them.

The zipfile i uploaded to JLCPCB i have put it as a download on the bitbucket mk14 repository. If you have any luck with it please tell me!
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Old 4th Mar 2020, 10:35 am   #265
SiriusHardware
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Default Re: MK14 schematic revisions

Hi Ian, Tim and I are considering having more boards made, although it might not be for a month or so due to time / looming financial commitments. (SWMBO has broken her car again).

If we present that zipfile to your PCB manufacturer, is that basically all that is required in order to have more of the boards made? Simple yes or no answer, we obviously don't want to tax you or stress you out at this time.
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Old 4th Mar 2020, 11:06 am   #266
Slothie
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Default Re: MK14 schematic revisions

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Originally Posted by SiriusHardware View Post
Hi Ian, Tim and I are considering having more boards made, although it might not be for a month or so due to time / looming financial commitments. (SWMBO has broken her car again).

If we present that zipfile to your PCB manufacturer, is that basically all that is required in order to have more of the boards made? Simple yes or no answer, we obviously don't want to tax you or stress you out at this time.
Yes, if you go to the JLCPCB site and upload the zip file the page unpacks it and fills out the dimensions and shows a picture of the top of the board. You can choose options like solder mask colour, plating etc. I just used all the defaults, aside fron adjusting the quantity down to the minimum (5).
Dont worry about stressing me, im bored as anything )
Im doing physio now to make me fit to leave hospital - up to about 6 weeks ago i couldnt even stand, now im walking up and down the ward with a walking stick, still very tiring but getting a little better every day. My cancer has been forced into remission by chemo for now so it just needs monitoring to make sure it doesnt return.
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Old 4th Mar 2020, 4:59 pm   #267
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
Thanks for taking the time to post this information, very useful. If at least two of the major optoelectronics manufacturers used it, then maybe this pinout was an established standard. I wonder how the odd / jumbled order of segment connections came about?

My MK14 is in storage so I can't check its original display just now but the display is highly likely to have been a Nat Semi part as the kits of parts for the MK14 were supplied to Science Of Cambridge by National Semiconductor.

The other 9-digit display I originally pulled from a Texet 880 calculator (and which I know works in the MK14) is a NSA1488.
According to the 1991 lite-on optoelectronic data book, the LTB-1498 may also be a suitable alternate.

I ordered a few on ebay from Netherlands last year, advertised as TIL393-3 or equivalent to NSA1166, but the photos are a nine digit display. I took a chance and ordered a set from him, delivered to my Mum in the UK to reduce postage and avoid customs fees. I havenít had chance to collect them and test to confirm they are ok, but photo sent by my Mum identifies them as LTB-1498.
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Old 4th Mar 2020, 6:31 pm   #268
SiriusHardware
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Default Re: MK14 schematic revisions

Mark1960, acknowledged, your post just made it through new member moderation. Thank you for that.

Ian: Unfortunately more members of my immediate family have been affected by forms of this illness than have not, so I have some appreciation, if only second hand, of the strain it can put you under.

Right, so if we just want more copies of the Issue VI boards which you already had made (but understandably have not been able to do anything with) we just upload that package, tick the boxes and hand some money over. We might even get the same 'first time customer' carriage discount if we are lucky, unless their system recognises that they have already made a batch of these boards of course. I wonder if they would make them in black? Black is such a Sinclair colour... could maybe even find a little rainbow stripe transfer to splash across one of the corners...

I seem to remember you had noticed some very minor errors such as screen printing overlapping one of the device part numbers and to that end I installed the Linux version of Kicad V5 and tried, in no particularly intelligent fashion, to see if I could load the project with a view to tweaking things like that. It didn't work on the first attempt but I have not made any attempt to fix things - for example I probably have to have the project files and library files in a particular directory structure relative to where the .PRO file is, so I'm going to look through the .PRO file to see if there are any paths specified and if so rearrange things so the files can be found where they are expected to be.

I've actually started a separate thread about Kicad, because lately a few people have expressed an interest in learning a bit more about it and quite a few others like yourself appear to know it quite well.

Last edited by SiriusHardware; 4th Mar 2020 at 6:58 pm.
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Old 4th Mar 2020, 8:19 pm   #269
Slothie
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Default Re: MK14 schematic revisions

The files in kicad are all text files so with a suitable editor you can search for pathnames etc. I tried to make them relative rather than absolute but its probable i was not completely successful remembering to do this. Dont forget the cache file keeps copies of footprints for pcbnew so you may need to edit pathnames in there too. In the past ive also written Python scripts to make bulk changes to Kicad files (e.g. change font size on resistor labels) so thats an option!6
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Old 4th Mar 2020, 11:58 pm   #270
SiriusHardware
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Default Re: MK14 schematic revisions

Got it! It was just a matter of going a few lines into the .PRO file and changing the path to point at the new location (in my Linux filesystem) of your library.

I've just been going for a fly-by around the board. I have to say, what a work of art! I shudder to imagine the hours which must have gone into getting it to that point.

That said, I am such a Kicad novice that I don't think I dare tamper with anything as I'd probably just end up with an impossible combination of parameters. Probably best to use the final output files from which your own PCBs were produced.
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Old 5th Mar 2020, 10:31 am   #271
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Default Re: MK14 schematic revisions

I think having existing files made means all three of us and anyone who wants to buy one of our spares will be working with the same baseline to find bugs and errors - some hand patches and wires will make it more authentic!
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Old 5th Mar 2020, 6:16 pm   #272
SiriusHardware
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Default Re: MK14 schematic revisions

Yes, I agree. I'm now starting to pull together the necessary parts.

Ironically, I have most of the 'hard' parts since I've long held an SC/MP II, an INS8154 and a display as spares for my original MK14.

I also have a spare set of programmed PROMs, I bought a pair of blank DM74S571s for what I thought was the expensive price of £6 each about two years ago - I would probably be lucky to buy blank DM74S571s for double that now.

Really the only 'hard' part I don't have is the RAM, and there Ian has provided for the possibility of using an alternative type of device.

I have some 74LS365s, the equivalent of the much harder to find 80L95, and I'm sure I have some 74LS157s because I bought a small quantity of those when one of the ones in my original 48K Spectrum went down.

7445, 7408s could prove harder to find, although I haven't really looked yet.
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Old 6th Mar 2020, 11:05 am   #273
Timbucus
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Default Re: MK14 schematic revisions

Just checked my box of bits and have like you almost all but, no 7408 - I do have 3 7445 and a stack of 74LS157 if you don't. On the 7408 and memory note I have been waiting to place an order for quite some time for a few projects from uTSource (and they have only just resumed delivery with a 2 week lead time) so if you want as I am going to be hit with import duty anyway I could add a few extra!

As well as the 7408 (at around $0.8) They do have stock of the AM2111DPC (at around $4 each with import duty) which is the 250ns version of the AMD equivalent - they also have the B (400ns ones) which I think I ordered last time and they worked.

Shout out if you want me to add anything on - have to wait until I find out how much my car is to repair though as it was brought home on a low loader last night before I commit!
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Old 6th Mar 2020, 11:34 am   #274
SiriusHardware
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Default Re: MK14 schematic revisions

I have most of the parts (7445, 74LS00, 74LS20, etc) on the way now and I did find my 74LS157s - I could really do with 4 * RAM ICs though, so I'll PM you about that.

Forum user 'KeithsTV' has very kindly offered 4 * 7408, so if he has no objection I will forward two of those straight on to you.

The ICs I have coming to me were all UK sourced, but it shows in the price - hard to believe that once common logic ICs are now so expensive. Part of my aversion to ordering from China is their great fondness for fakes, there was something odd about the 74LS365 you originally had in the JM PCB, it seemed to be a retopped / reprinted device, as I recall.

Of course there's no guarantee that devices which are already in the UK are not just more expensive fakes.
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Old 6th Mar 2020, 5:13 pm   #275
Slothie
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Default Re: MK14 schematic revisions

I bought my 7445s from Farnell who had a small stock but that was about a year ago. They do pop up on eBay from spain from time to time.
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Old 6th Mar 2020, 5:40 pm   #276
Slothie
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Default Re: MK14 schematic revisions

Oh the pcb hasc2 jumpers on the bottom to select memory type (pre-wired to x2111 by a thin trace between the pads) and another pre-wired to 0v that pulls the sense lpin down. If you want to use the sense pin on the edge connector cut the thin ttace between the pads. Alternitovely you can cut the trace and solder a 1k surface mount resistor between the pads and it will default to 0v but youll be able to pull it up by a circuit connected to the efge connector.

Thanks for all the kind comments. I taught myself Kicad by designing PCBs for several of Grant Searls single board computers and a few arduino based citcuits (none of which i have had made, but it taugt me a lot) i also did a board for the Acorn 1 CPU board thst was a challenge, again i never actually had made, so the 2 versions of the MK14 are the only boards i have had manufactured.
I have found Kicad quirky but ultimately very powerful. Getting your head around the librarys and editing them, which is why the project is a bit of a mess and includes a lot of libraries it doesnt use. If. I wae doing it again Id create a library in the MK14 project and import schematic symbols that are usef into it, so it is the only library you need and changes to the Kicad lubraries wont stuff up your design. Likewise for the footprint libraries.
I will admit Kicad is not as easy to use as, say Eagle, but i stopped using it when they went to a subscription modeland the PCB size restrictions were limiting (to do the MK14 id have to buy the professional licence for tjousands....) In other words Kicad is in my mind worth the effort - just make sure you have a big screen or 2 and a decent mouse. I have used it with the touchpad on my laptop but it was far, far better with a mouse!
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Old 6th Mar 2020, 5:55 pm   #277
Slothie
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware
That said, I am such a Kicad novice that I don't think I dare tamper with anything as I'd probably just end up with an impossible combination of parameters. Probably best to use the final output files from which your own PCBs were produced.
If you run te design rules check after making changes it will tell you about any tracks that are too close etc, i have configured it to JLCPCBs requirements. You will get a number of errors about missing connections on the keyboard as kicad ignores hthe copper thats part of the switch footprint - one of Kicads bugs/features. I carefully checked each line of the report and ignoref the ones that mentioned the switches.
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Old 6th Mar 2020, 6:11 pm   #278
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Default Re: MK14 schematic revisions

Yep, I still favour a desktop PC, an actual push button keyboard, a real mouse and a screen the size of a door for doing... well... just about anything really. I don't do mobile devices or applications at all, and especially not touchscreens.

Now that I've been able to look at it properly the board really looks lovely and I did notice the little touches like the (eminently sensible) Sense-A link and the 'Sloth' logo as well. . The screen-print identification of all of the edge connector connections is especially welcome. All these improvements, including the alternative-RAM option (and the buses tracked to the rear edge of the board at long last) mean the the PCB really does deserve the accolade 'issue VI'. Like Tim, I think it is best that all three of us will be using boards which are identical to your original batch so I'm not going to mess with it.

I do have a single, rather expensive 7445 on the way to me at the moment.

It was only a few months ago that someone mentioned that Farnell / CPC had drastically downsized their discrete logic range - I've just checked, and there are no (non LS) 7445s available there now. I see that for the time being most of the required 'LS' logic (00, 08, 20, 173, 157, 365) can still be had from Farnell in DIP packages at not-bad prices. They are mostly Ti (Texas) SN family devices but that is 'allowed', as some of the ICs which came in my original MK14 kit were Ti 'SNs' as well.
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Old 6th Mar 2020, 6:24 pm   #279
Slothie
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Default Re: MK14 schematic revisions

If you do use my gerbers and drill files then I can correct any errors on my design should there be any.
All the TTL on my original prototype where Texas including the 7408s which were 1978 Cerdip oned. Its a shame i cant get to my stock because i have 40 left from the lot i bought off eBay!
I am pretty sure i adding in proper decoding of the PROM so you can add extra RAM from 200-7FF.

Last edited by Slothie; 6th Mar 2020 at 6:30 pm.
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Old 7th Mar 2020, 7:34 pm   #280
SiriusHardware
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Default Re: MK14 schematic revisions

Yes, that was the last major change as I recall it, the squeezing in of an extra IC so that you could remove the PROM images while still retaining the alt-RAM feature.

The removal of the PROM images from 0200-07FF combined with the routing of the buses to the rear edge connector creates the possibility of making a RAM pack, in finest Sinclair tradition, which just plugs into the rear edge connector for an instant extra 1.5K of memory.

At its simplest, this would be a single 8-bit wide static RAM and an address decoder, but getting progressively more complex, it could have settable links so that parts of the RAM would be paged in when the 512 bytes of onboard RAM and 'Extra RAM' region addresses were activated, removing the need to find obsolete, expensive 2111s, etc.

Taking that one step further, the PCB could also have a socket on it for a 2716 EPROM which would drop in whenever an address in the remaining PROM image ranges was accessed, thereby also removing the need for difficult to obtain / difficult to program bipolar PROMs.

Finally, any such add-on would ideally need some bus buffering and of course a one to one DIN connection on its own rear edge for the MK14 VDU.

Another good touch that I noticed was the replacement of one of the two 0V connections on the keypad edge connector with a reset-input line so that an external reset switch can easily connected, especially useful if the PCB will be mounted in an enclosure with a remote-mounted keypad and display.
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