MK14 schematic revisions

[SiriusHardware]

Tim, you could try bumping your A8-A11 capacitance up to 200pF as that has no adverse effect on mine and everything runs reliably, no artefacts with OrtonView attached.

I actually like the keyswitches I have with the clear caps but I would be interested in an increased-height version of the lower 'waffle' frame only so that it would serve as a frame / guide / surround for the taller switches and caps. To work for that purpose it would need to be printed to a thickness of about 7.5mm and printed slowly / with a high degree of resolution, because it would be 'on show'. Oh, and it would have to be black.

[Timbucus]

Originally Posted by SiriusHardware

Tim, you could try bumping your A8-A11 capacitance up to 200pF as that has no adverse effect on mine and everything runs reliably, no artefacts with OrtonView attached.

I actually like the keyswitches I have with the clear caps but I would be interested in an increased-height version of the lower 'waffle' frame only so that it would serve as a frame / guide / surround for the taller switches and caps. To work for that purpose it would need to be printed to a thickness of about 7.5mm and printed slowly / with a high degree of resolution, because it would be 'on show'. Oh, and it would have to be black.

I will give that a go if I see the reverse C again even once.

Yes - I would quite like the same to stop the rotation of the keys but, I am happy with the result and the splashes of red and yellow in this instance as I have green PCB's as addons.

I think maybe with a higher version it might be necessary to make it honeycomb perhaps and slightly oversize - you would then finish the outside as the only real way on a 3D print.

I will do some cassette interface testing to prove you can move between machines perhaps as my next video topic and as an excuse to play with it...

[Slothie]

I've designed a sexy 3D printed frame with 3D printed keycaps, just need a 3D printer to try it out on! I bought the keyboard frame because it looked OK. I think if you wanted a modified one to stabilize the ordinary keycaps you might need to modify the eBay one slightly unless the holes are square and ~12.5mm. Oh, and the riser will need to be thicker as Sirius noted. To get a nice finish the best way aparently is to print it face-down on a glass print bed. The ones being sold have a textured surface but thats not to say it couldn't be sanded and polished (I beleive PLA and ABS take to this reasonably well).
Plenty of things for me to experiment with.
I have all the components for a tape interface but I've not bothered as yet because all my tapes and players (you guessed it...) are in storage. I've had success with loading from an Arduino connected to the serial in and using the OS routines, although my experiments with the timing have not been conclusive or reliable (hence no results reported!)
I got a package with some mosfets and voltage converters in this week, wonder what I can do with those?

[Mark1960]

Well I shifted the display two pins to the left and two pins to the right and in both cases the weak digit was still in the same position on the display module.

As its still useable, I’m just going to leave it alone, at least until I have a possible replacement.

Tim, any chance I can get a copy of the gerber files for your display pcb?

[Timbucus]

Originally Posted by Mark1960

Well I shifted the display two pins to the left and two pins to the right and in both cases the weak digit was still in the same position on the display module.

As its still useable, I’m just going to leave it alone, at least until I have a possible replacement.

Tim, any chance I can get a copy of the gerber files for your display pcb?

Well that is at least confirmation it is the module.

It is not my PCB design but a seller named Trevor Hamblett whose bay username is trev-ham. He does not have any listed at the moment but, used to have a listing with some photos of the options - maybe a message to him would be an option.

[Slothie]

Originally Posted by Timbucus

It is not my PCB design but a seller named Trevor Hamblett whose bay username is trev-ham. He does not have any listed at the moment but, used to have a listing with some photos of the options - maybe a message to him would be an option.

I have a couple of those .28" modules I was going to use for my MK14 (Eyesights not what it used to be!) so if anyone is thinking of using the .28" displays and messages trev_ham I'd be interested in one or 2 if he doesn't want to make just one. I was going to use perf-board and hot-glue but a PCB would be neater!

[Mark1960]

For me it’s probably better just to create a set of gerbers and order direct from jlcpcb, rather than paying for shipping to Canada, then I can get matching colour too. Shipping from China will be shared with a couple of others that are still just ideas.

Would be nice if i could get the displays to fit in the hammond calculator style case, for a Pic14, but the four digit 0.28” displays are a little wide without cutting the case. I might look for an alternate case or see if there are any smaller displays. Bubble calculator display would work but wanted to try and use current components only for this.

[SiriusHardware]

I confess I'm surprised how well 'large' displays seem to work because I would have thought the current required for reasonable segment brightness on a big display would be beyond the ability of the 7408s to supply it.

I assumed (without even thinking about it) that the large displays which were available at the time must use additional driver circuitry (ULN2xxx, etc) to boost the original feeble drive which was only ever meant to drive a bubble display.

[Slothie]

Originally Posted by SiriusHardware

I confess I'm surprised how well 'large' displays seem to work because I would have thought the current required for reasonable segment brightness on a big display would be beyond the ability of the 7408s to supply it.

I assumed (without even thinking about it) that the large displays which were available at the time must use additional driver circuitry (ULN2xxx, etc) to boost the original feeble drive which was only ever meant to drive a bubble display.

Modern LEDs are 100 times brighter than their 70's counterparts. The 7408 has a ~200 ohm output impedance, so its capable of delivering ~15mA to an LED which is plenty. They probably could have driven larger displays but I remember buying a single digit 7 seg display by mail using a postal order for what I recall was about 60p - about £3 in todays money - so I presume the bubble display was a cost-cutting measure too.

[SiriusHardware]

Speaking of displays, I have been doing a little bit of messing about this weekend to keep the MK14 'scene' alive. Attached, my issue VI driving a 2-line LCD display (display based on Hitachi HD44780 or clone controller IC).

The display is being driven from PORTB of the 8154 in 4-bit, write-only mode. The display EN (enable) pin is active-high and I found it necessary to have a pulldown on that line so that the display is not enabled when the 8154 is in its default all-inputs state.

Needs fine-tuning for speed - some display commands take the display longer to process than others - and then I'll try scrolling a message in the tradition of 'Message'.

[Slothie]

That looks fun! I have been thinking about ptojects to do with my MK14 and never thought to break out any of my Arduino sensors etc.

[Timbucus]

Nice one Sirius - this is the way to go now to add on peripherals like the Arduino and PI have. I have quite I few I keep meaning to try - 1st step is to port my bitbang i2c code from the Z80 though. Still head down on my Triton at the moment but, close to having a fully complete setup so the SC/MP is beckoning me back.

[SiriusHardware]

The next thing I was considering was rigging up a MIDI output - little more than a transistor and a couple of resistors - for once I wouldn't feel bound to optocouple it as MIDI inputs (on instruments) are already opto isolated. Initially I'd probably just try converting 'Music Box' to send its output over MIDI.

The MK14 doesn't quite have enough memory for a full blown 'tune tracker' but it could probably hold a few drum patterns (I have several MIDI synths with built in drumsets) so it could form the basis of a programmable drum machine.

At that point it would probably be best to use an offboard oscillator to provide a metronome 'tick' signal on Sense-B rather than try to do it all with software timing.

[DeltaAlpha52]

Hi been a while but now the Nascom 2 is working again - and my emulator - I was looking to sorting out the MK14, and was looking at using the larger displays. Has anyone managed to sort out those PCB display boards or get some design files ?

My current setup uses a bigger display but on a veroboard and is a bit messy

[Timbucus]

Originally Posted by DeltaAlpha52

Hi been a while but now the Nascom 2 is working again - and my emulator - I was looking to sorting out the MK14, and was looking at using the larger displays. Has anyone managed to sort out those PCB display boards or get some design files ?

My current setup uses a bigger display but on a veroboard and is a bit messy

They were made by trev_ham on the bay but, he no longer lists them or indeed any item for sale so not sure how we could contact him to ask if he would make more or release the PCB. It is small enough for someone to design one I think but, not aware that that has happened.

[Mark1960]

I was going to lay one out, but still not got round tuit.

[Mark1960]

Originally Posted by DeltaAlpha52

My current setup uses a bigger display but on a veroboard and is a bit messy

What display type did you use? Do you have a schematic or sketch of connections?

[SiriusHardware]

According to Slothie modern discrete 7-segment displays are a lot more efficient (produce more light for the same current) than the eighties equivalent. That being the case you can presumably just take a set of 8 * common cathode displays and common all the a-h lines to make them the electrical equivalent of the original multiplexed bubble display.

If using older displays you'd probably need to add ULN28xx drivers for the a-h segment lines and possibly the column / cathode output lines from the 7445, as Buzby did when he fitted his larger display to 'Micky' back in the day.

[ChrisOddy]

I have Trevor Hambletts email address if anybody wants to contact him, PM me.

Chris

[Slothie]

I was going to do a layout for a LED board but couldn't find a reliable supply of small LED displays. I have got some small displays from China but they are clock displays (colon replacing one of the decimal points) and dissapeared soon after. Other than them the smallest generally available in common cathode is 0.3" which is a bit large for what I wanted so I never sat down and laid out the PCB.