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Old 13th Oct 2021, 1:46 pm   #781
DeltaAlpha52
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Default Re: MK14 schematic revisions

Hi all

Thought I'd just mention an issue I had with reset using the MK14keys interface. This is using Martin PCB that has the reset line connecting to 5v.

Using my old MK14keys interface, before building the new one from Slothie ( thanks ), I realised that when the MK14 was running a program, like message, the interface was not able to reset the MK14. The physical reset button did work and it could reset the MK14 when just the monitor was running.

Did a check and found that the voltage across the capacitor was over 2.8 volts when the reset was active. It seems that this was not low enough to trigger a reset in all situations.

I had a number of ASSR-1218 MOSFET Solid State Relays left over from another project. These are pin compatible with the PC817C - although it has 2 relays in 1 package. Replaced the PC817C and the voltage across the capacitor during reset dropped to 0.27v and reset occurred in all cases.

Changed the PC817C opto chip for a new one and then it got the voltage down to 2.2 and the reset worked in all cases.

Thought I report it in case others had the same issue.

Stay safe
David
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Old 13th Oct 2021, 5:13 pm   #782
SiriusHardware
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Default Re: MK14 schematic revisions

To be honest I'm surprised the pulldown from the opto output is as poor as that - obviously the opto output is polarity conscious so on a 'Martin' with its unique inverted reset circuit the opto output collector needs to go to the +5V rail (+ve of the reset capacitor) and the opto emitter needs to go to the reset circuit input, the -Ve of the reset capacitor in this particular case.

I'll have to fire mine up and see what reset low level I get from mine, which uses TLP185 optos and 330R opto series resistors for both 3V3 and 5V hosts.

The voltage across the capacitor will never quite go all the way to zero because of the 120R resistor in series with the opto collector - that is there to stop the charge held in the reset capacitor from being discharged instantly through the reset-opto transistor when it turns on.
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Old 14th Oct 2021, 7:02 pm   #783
DeltaAlpha52
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Default Re: MK14 schematic revisions

Well it seems it might have just been that one chip - tried a couple of spare ones and they all work fine.
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Old 14th Oct 2021, 10:09 pm   #784
DeltaAlpha52
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Default Re: MK14 schematic revisions

Think I found the issue - I used a 330R on the reset line rather than the 120R - probably just got carried away as all the other resistors are 330R.
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Old 14th Oct 2021, 11:29 pm   #785
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Default Re: MK14 schematic revisions

The prototype didn't have a series resistor for the reset opto collector but I soon realised that it wasn't a good idea to use a tiddly transistor (max: 50mA or so collector current) to instantly discharge a charged electrolytic, even a relatively low value one.
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Old 27th Oct 2021, 6:38 pm   #786
DeltaAlpha52
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Default Re: MK14 schematic revisions

I decided I'd like to try the .56" displays - so I did dome kicad work and produced a board that uses the .56 displays.

I also had some 3x3 displays that had a veroboard interface - so I decided that a nice PCB would be in order. It uses Oasistek TOT-3301AH-N that I found on the internet.

See pictures

So now I have 3 different plug in display boards - the only advantage of the 3x3 board is that you can activate the 9th digit

I have a couple of spares so if anyone wants one please PM me and let me know. I'll put up a link to the kicad files when I have tidied them up.

Cheers David
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Old 27th Oct 2021, 7:52 pm   #787
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Default Re: MK14 schematic revisions

Those .56 would be great at shows and demos!
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Old 27th Oct 2021, 8:52 pm   #788
DeltaAlpha52
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Default Re: MK14 schematic revisions

My only worry was that they would draw too much current - Trevor was worried about that - so I had to do my own PCB. I'm not sure if it is just the ones I have got but it seems to work okay. Maybe I should have included space for limiting resistors on the PCB

David
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Old 27th Oct 2021, 9:32 pm   #789
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Default Re: MK14 schematic revisions

Slothie has suggested that modern 7-segment LEDs are a lot brighter for less current than their equivalents from 30 years ago, so maybe you could insert series resistors and not lose too much light output.
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Old 27th Oct 2021, 10:28 pm   #790
Mark1960
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Default Re: MK14 schematic revisions

Are the 4 x .56” displays a common pinout ?

I recently received some three digit displays, I think too small for your board. 3 x .25” digits, only 15mm wide so 9 digit display is same size as bubble display, but larger digits. I got the common cathode red with decimal point, but also available in other colours, common anode and no decimal points.
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Old 28th Oct 2021, 7:03 pm   #791
DeltaAlpha52
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Default Re: MK14 schematic revisions

Here are the pinout for the HS420561k-32 - I think it was similar for the smaller displays.

The 3x3 ones are different - they are (0.30”) 8.0mm digit height
and the layout is

g. f. Gap. p. a. b. top pins
8. 8. 8. DISPLAY
1. 2. 3. e. d. c. Bottom pins

1. 2. 3. are the common Cathodes
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Old 6th Nov 2021, 5:32 pm   #792
DeltaAlpha52
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Default Re: MK14 schematic revisions

I have put the kicad and gerber files up on github if anyone wants to take a look.

https://github.com/dallday/MK14displays

I have a few of the boards available if anyone needs them.
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Old 7th Nov 2021, 12:20 am   #793
Timbucus
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Default Re: MK14 schematic revisions

That's great David thanks - I will probably get another one made up at some time!
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Old 10th Nov 2021, 3:04 pm   #794
DeltaAlpha52
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Default Re: MK14 schematic revisions

I do have a couple of spares if you want to PM me
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Old 12th Nov 2021, 7:47 pm   #795
DeltaAlpha52
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Default Re: MK14 schematic revisions

Seems there is another MK14 for sale on the e site

Looking at the pictures it seems to have a mod board plugged into the 8154 socket and what seems like a flying lead from the right rom socket - probably to provide the ROM enable - anyone come across this mod before?
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Old 12th Nov 2021, 9:55 pm   #796
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Default Re: MK14 schematic revisions

I think it's only fair to warn you that discussions about current auction site items are against the forum rules, David, even if only to discuss them from the point of something about them which is unusual.

It sounds as though someone has used a more modern EPROM to contain the OS instead of two Bipolar PROMs, rather like Slothie's adaptor which has been discussed elsewhere.
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Old 12th Nov 2021, 10:51 pm   #797
DeltaAlpha52
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Default Re: MK14 schematic revisions

okay - warning noted.
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Old 12th Nov 2021, 11:03 pm   #798
DeltaAlpha52
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Default Re: MK14 schematic revisions

I was interested in that he had used a different way to add a modern ROM chip - all the data lines and the low address lines are available on the 8154 ( I think ) and he has just done 1 flying lead for the select
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Old 12th Nov 2021, 11:18 pm   #799
SiriusHardware
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Default Re: MK14 schematic revisions

I had to think about why the 8154 would have the low address lines going to it but of course it includes 128 bytes of RAM doesn't it - I would have thought (with the ROM being 512 bytes) A8, possibly A7 as well would have to be picked up from somewhere else, maybe they are but it's not very obvious.

I don't think I would do it that way myself, the 8154 is just too useful to not have installed, although good luck finding one for reasonable money nowadays.
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Old 12th Nov 2021, 11:26 pm   #800
Slothie
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
I had to think about why the 8154 would have the low address lines going to it but of course it includes 128 bytes of RAM doesn't it - I would have thought (with the ROM being 512 bytes) A8, possibly A7 as well would have to be picked up from somewhere else, maybe they are but it's not very obvious.

I don't think I would do it that way myself, the 8154 is just too useful to not have installed, although good luck finding one for reasonable money nowadays.
Address lines a0-a8 and a11 go to the 8154 (a8 & a11 go to the chip selects of the 8154). I had toyed with the idea of making a plug in module that replaced the 4 256 byte segments of memory at the 8154 occupies at 8xx,Axx,Cxx and Exx with RAM from 2 2114 chips, for applications that don't need a 8154 but would benefit from the extra 1k RAM. You'd have to get the a9 and a10 from flying leads though.
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