25th May 2022, 7:38 pm | #821 |
Tetrode
Join Date: Feb 2020
Location: Crawley, West Sussex, UK.
Posts: 77
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Re: MK14 schematic revisions
I do have a 8154 and extra memory chips to fully populate the new board thanks to members of this forum.
Had not plugged them in just in case I had something wrong - now it seems to be working I'll have to get them from the box of MK14 bits and plug them in and test it all. And as for display I do have the even bigger display using 2x4 .56 segments (HS420561k-32) but the one shown use 3x3 .3 segment units - giving 9 digits. And I remember doing a mod on my original MK14 to activate the 9th digit (PCB details on github if anyone is interested ) |
25th May 2022, 9:08 pm | #822 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,553
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Re: MK14 schematic revisions
If the display gets any bigger any small objects which happen to pass by will be captured by it and start orbiting around it.
My 60-year old eyesight is as bad as to be expected, or at least my near sight is, but I can still see and still prefer the original bubble type displays as that was all part of the 'fun'. Note though that I can be remarkably selective where nostalgia is concerned: Peering at small displays, fine. Taking 20 minutes to type code in... not so much. |
25th May 2022, 9:33 pm | #823 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,294
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Re: MK14 schematic revisions
I just wired up a 3x3 display using 0.25” high displays. Similar size to the bubble display but better viewing angle. It seems to me that the digits vary in brightness depending on the digit displayed. F is brightest, 1 is noticably dimmer. I included 1k resistors on each segment drive but can’t think why that would change the brightness depending on the digit displayed. Maybe its due to timing of the MK14 display driver routine. Choice of 1k resistors was due to having that value in 0603 SMT as it was easier than using leaded resistors. I might try to piggyback another 1k on top of the others.
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25th May 2022, 10:10 pm | #824 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
If the 'on' resistance of the common cathode 'sink' switch (ie, 7445?) is not a perfect zero ohms then the more segments you have lit, powered in parallel and passing their sink current through that common connection, the more the voltage at the common cathode connection will rise, lessening the overall voltage across each segment and its series resistor.
Try scoping the common cathode connection of one display cell and nothing the value of the 'active low' voltage on that connection when that display cell is displaying various different characters. Edit: Just noticed that for you, 'F' is actually brighter than '1'. That -is- weird. |
26th May 2022, 12:10 pm | #825 |
Tetrode
Join Date: Feb 2020
Location: Crawley, West Sussex, UK.
Posts: 77
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Re: MK14 schematic revisions
Funny that I thought about adding resistors to the PCBs I made but since the one I got did not have any resistors I "hoped" they would not need any. All mine seem to be okay but very bright, maybe some way of adjusting the brightness would be useful.
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27th May 2022, 2:43 am | #826 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,294
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Re: MK14 schematic revisions
I’ve added 1k resistors in parallel, this improved the brightness in room lighting but 1 is still less bright than all other digits regardless of position in the display. It seems to be only 1s that are affected, no visible difference between any other digits.
Its not a big problem, just curious what might be causing this. One reason I added resistors is that I’m going to try replacing the 7408s with 74hct08s. |
29th May 2022, 12:13 am | #827 |
Pentode
Join Date: Jun 2012
Location: Bristol, UK.
Posts: 115
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Re: MK14 schematic revisions
I believe this is an eye/brain thing?
If all segments are the same then the number illuminated will give varying 'brightness'. Also "1" is minimum width. |
29th May 2022, 6:33 am | #828 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: MK14 schematic revisions
Well I think I found a bug in the SoC monitor. In the loop that drives the display, it reads the segment data from memory, writes the segment data to the display, then performs DLY 00 without setting the accumulator to specify the delay length. The delay for each digit is dependent on the segments set for that digit. Digit ‘1’ has a value of 6, digit ‘7’ has a value of 7, all others have a value greater than 63.
It might not be noticed with no resistors in the segment drive as the 7408s may be current limiting with a slight delay after being driven high. I haven’t confirmed the issue with 7 yet, my VI is in pieces due to trying to get a second VI running. |
29th May 2022, 9:07 am | #829 | |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
Quote:
Amazing how problems like this can stay hidden for nearly half a century, mainly because the monitor was developed and run (by most people) on unaltered hardware.It's only when people start playing around and changing things that issues like this come out of the woodwork. The solution would be what, to use an active constant current circuit in the feed to each segment, rather than a resistor? |
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29th May 2022, 9:49 am | #830 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
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Re: MK14 schematic revisions
If it's unnoticeable on the original hardware, is it really a bug? The MK14 as sold produced a readable display and nobody saw any brightness issues
Even with the modified hardware it's only really a cosmetic problem isn't it? The display is readable. |
29th May 2022, 10:02 am | #831 |
Dekatron
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Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
It's the kind of imperfection we love to pick at.
I personally have never felt the need to change or enlarge the display even when, for a period of time, I had mine mounted off board (along with an external keypad). |
29th May 2022, 11:38 am | #832 |
Pentode
Join Date: Jun 2012
Location: Bristol, UK.
Posts: 115
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Re: MK14 schematic revisions
Yes, I know about the 2(AC) in the DLY equation. And Yes, I'd forgotten about it (*).
Remember, only one digit is illuminated at any time. If my figures are correct the DLY can vary 'digit lit' by up to 242 μcycles. The minimum display ('1') is 159 μcycles. Do you find a '7' looks dim? It has a DLY only 2 μcycles longer than '1'. But 50% more LED. There's some really amateurish code in the original SCMPKB monitor (Shame on you NS!). When SoC hacked SCMPKB into SCIOS that code remained. To be fair, I believe SoC were working without an Assembler. So they made the minimum changes. And I think their listing was done manually. An example is at x01FC - should be L(ABORT)-9 NS annotation wasn't changed - can be misleading or wrong. As x01FF (*) I run a monitor with LDI 0 before the DLY 0. |
29th May 2022, 5:18 pm | #833 | |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
Quote:
However, even I could not have predicted that it would irritate you so much that you would customise your OS to eliminate it. |
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29th May 2022, 6:48 pm | #834 | |
Tetrode
Join Date: Feb 2020
Location: Crawley, West Sussex, UK.
Posts: 77
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Re: MK14 schematic revisions
Quote:
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29th May 2022, 7:02 pm | #835 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,294
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Re: MK14 schematic revisions
I had 1k resistors in series with each segment, and then added additional 1k resistors in parallel with each of those series resistors, giving 500 ohm resistance in series with each segment.
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29th May 2022, 8:26 pm | #836 |
Tetrode
Join Date: Feb 2020
Location: Crawley, West Sussex, UK.
Posts: 77
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Re: MK14 schematic revisions
Thanks - understand now
Interesting fact about the display driver and the DLY instruction. Just taken a careful look at my larger displays and it does look like the 1s are slightly less bright than the 0s. Without any resistors the display is quite bright. The difference might be more noticeable with the resistor and therefore dimmer overall. |
4th Jun 2022, 5:25 pm | #837 |
Octode
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,363
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Re: MK14 schematic revisions
Had anyone seen or heard of these addons and a major conversion of the MK14 from an advert in ETI July 1980 - a Z80 based MK14? The VDU sounds like the PE one hanging off the RAMI/O but, the printer sounds interesting as it works on an unexpanded MK14...
https://worldradiohistory.com/UK/Ele...1980-07-80.pdf |
4th Jun 2022, 11:42 pm | #838 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
Imagine if there is one of those (a Z80 converted MK14) still out there in the wild somewhere? I doubt if there were more than 10 of those conversions sold but I would love to be proved wrong. This is the first I've heard of it, sorry. If anyone did already know about this it would probably be circuitryboy.
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5th Jun 2022, 5:29 pm | #839 |
Octode
Join Date: Mar 2011
Location: North Yorkshire, UK.
Posts: 1,115
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Re: MK14 schematic revisions
Redditch Electronics address is just an ordinary terraced house - must have been a bedroom cottage industry...
Here's another ad: https://worldradiohistory.com/hd2/ID...-Page-0121.pdf Last edited by Phil__G; 5th Jun 2022 at 5:45 pm. |
10th Aug 2022, 8:30 pm | #840 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
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Re: MK14 schematic revisions
I've just been on one of my semi-regular trawls for 'new' MK14 related material and found this video tour of a distinctly unrestored MK14 + VDU + cassette interface coincidentally posted by Jim Austen at The Computer Sheds, just being discussed in another thread.
https://www.youtube.com/watch?v=WFwvY6zKkco |