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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 5th Jul 2020, 11:32 am   #361
Timbucus
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Default Re: Recreating the Bywood Scrumpi

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I am currently working out why he used such a resistor network for the 555 it does not lead to the 1Hz in Step 12 he says and we have produced. I also cannot work out why there is a pullup on the 555 Pin 3 -> Clock input on the 74C74 it is not needed as far as I can see.
I think the high level output voltage of the 555 with 5v supply does not meet the minimum high level input voltage of a cmos input. Typical is only 3.3v, but minimum is 2.75v
Thanks Marc yes obvious duhh - as I have used only the LS versions I never suffered. I will get some 74C74 and test (and let people know in the notes) - this will need a resistor on the back of the board to correct - which is OK as the original did but, for the D pullup. Thanks for that.

For those following he also used the upper section of the 7474 so it is Pin 11 that is connected to Pin 3 on the 555 not 3 as on ours.

The slight change that r1 in the astable (provided by R5 at 47K) makes is to lengthen the Ton to 3.6ms from 0.65ms with Toff remaining at 0.32ms which means the Slow step frequency remains around 1Hz. I will swap one of mine out and prove it still works or what if any impact it has on the single step especially. On our board that means swapping R4 for a 47K.
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Old 5th Jul 2020, 11:42 am   #362
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Default Re: Recreating the Bywood Scrumpi

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Don't be concerned Phil, I have a very, very 'dry' way of 'speaking' so it is not always easy to tell when I am being serious or when I am joking even when you meet me face to face. I should be more careful to use emojis or more obvious language when I write here.

I am not mad at you or anyone, and as I said I admire what everyone here is trying to do. It is a great pity that MJK did not go on to fulfil his full potential, I agree.
I also suffer from this with sometimes oblique jokes - so just assume we are joking... I am not sure I have ever seen a bad word on this forum which is why I like it so much.

On the JMK point it is why I have been driven to do this. I also agree that the BYWOOD ads did look unprofessional - and perhaps it was that human and "not polished" look that attracted me to them BITD as a hobby constructor - I was obviously eventually swayed by the eventual ZX80 slick colour advertising on what I did. It reminds me very much of my own early journey I suppose as our early adverts and inlays were definitely on the BYWOOD side with art drawn by school friends or even me but, we did strive for the SoC/Sinclair approach by the end with slick professional artwork.
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Old 5th Jul 2020, 11:52 am   #363
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don't be mad where's the English humor
of course scrumpi is not a successful system a little amateur low cost I think it has made a little bit of success
to program in binary what a galley and to light leds!
I think that the creator of this series was with a small team at the very beginning of computers.
He didn't have the support that Clive Sinclair had much more business with two genius engineers and the way was paved for the idea of a hobbyist kit.
but I love my MK14 martin.
And finally it's giving MJK back some of the glory.
maybe the scrumpi3 would have surpassed the mk14 it was already announcing the zx80
but then that's English history.
I think that it may have given the ZX80 a run for its money in the general market as well if he had made it able to run NIBL early on (after all the SCRUMPI 3 was available in March 1978 at least a year before) his real competition was the NASCOM. Why he avoided NIBL I don't know probably the eye watering cost of the NIBL ROM's and all his language is around placing it in the industrial space for control and development. As you say it was only him from an engineering perspective and his wife (Jane - probably her who signed the letter EJK) for Business admin. His volume was low as well and he would not have had the Capital or standing to pull down large volume part supplies to get cost down.

Last edited by Timbucus; 5th Jul 2020 at 11:53 am. Reason: minor typo
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Old 5th Jul 2020, 3:29 pm   #364
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Default Re: Recreating the Bywood Scrumpi

I've noticed something that is probably a US phenomenon: addition of a current loop interface to something like a Mark 8 (an early switches and LEDs machine) to enable it to drive a teletype. Add some memory and you could be running BASIC on said machine.

I can't see that expansion path ever working in the UK. Who in the 1970s owned a teletype? Or any kind of terminal for that matter?

No, a BASIC-capable machine for the UK market just had to have a built-in keyboard and VDU, and that meant a big cost jump.

So who were buying the systems with current loop interfaces on them?
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Old 5th Jul 2020, 4:10 pm   #365
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yes nostalgia when you hold us what an epic.
let us return to our machine no problem of voltage CMOS.j uses a 74c74 and I am in the process of realizing the pcb to the exact copy.
in fact it is the second flip-flop that is used the input D is at +VCC R11 is the pullup of RUN/HALT CS4 and R8 is the pullup of SLOW and STEP CS2/CS3
I make some tests on my board to check the resistance underneath to an unknown function and the pullup of the NE555 output is useless but I'll test with without
of course the plan is not complete in the brochure.
Amateur hour is in the air.
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Old 5th Jul 2020, 4:10 pm   #366
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I imagine a lot of colleges would have teletypes and American electronics magazines had numerous TV Typewriter and VDU projects. I had a GE Terminet 300 Teketype in 1980 my father rescued from a skip when they were upgrading to VT100s so I imagine other hobbiests did. I interfaced it to my PET to use as a printer.
But you're right, home computers only really took off when they had TV interfaces and built in keyboard.
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Old 5th Jul 2020, 4:11 pm   #367
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there's amateur hour in the air.
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Old 5th Jul 2020, 4:45 pm   #368
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Default Re: Recreating the Bywood Scrumpi

Tim, you must be happy.
in my youth as a DIY ADO I was reading the magazines. the scrumpi had caught my eye and I liked the mk14 very much.
I had considered ordering a zx80 and then the time spent on a zx81 kit but each time my pocket money was very low and I waited by making different assemblies with salvaged parts.
finally I transformed my TI30 in high school into a programmable machine the whole in a wooden box with RAM multiplexer demultiplexer keyboard and switch for programming step by step not a jewel for me my.
Industrial design teacher was not coming back
unfortunately I'm no longer this machine and I can not find the plans that I had modified and adapted to my project.
my first computer was a VIC20
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Old 5th Jul 2020, 6:49 pm   #369
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Default Re: Recreating the Bywood Scrumpi

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I've noticed something that is probably a US phenomenon: addition of a current loop interface to something like a Mark 8 (an early switches and LEDs machine) to enable it to drive a teletype. Add some memory and you could be running BASIC on said machine.

I can't see that expansion path ever working in the UK. Who in the 1970s owned a teletype? Or any kind of terminal for that matter?

No, a BASIC-capable machine for the UK market just had to have a built-in keyboard and VDU, and that meant a big cost jump.

So who were buying the systems with current loop interfaces on them?
That was one of the main things that J.M-K was aiming at with SCRUMPI as you did not need a terminal however he still included a 20mA interface on the SCRUMPI3!

The only place I saw terminals was school and college - I cannot remember anyone I know having one - it was that move to things like the NASCOM having a BASIC and a keyboard/VDU that moved computing in the UK to the mainstream you are correct.
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Old 5th Jul 2020, 8:25 pm   #370
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Default Re: Recreating the Bywood Scrumpi

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Old Yesterday, 5:57 pm   #371
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Default Re: Recreating the Bywood Scrumpi

sorry
the pcb's have arrived
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Old Yesterday, 6:06 pm   #372
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Default Re: Recreating the Bywood Scrumpi

the tests to correct the circuit as the original are finished the bywood plan is ok but still to redo the pcb
mike's welded-on resistor is useless.
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Old Yesterday, 9:12 pm   #373
Timbucus
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Default Re: Recreating the Bywood Scrumpi

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the pcb's have arrived
They look really cool - I also had a nice delivery today...

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and some 3mm LED's with resistance are on order - I am NOT soldering resistors to 20 LED legs ever again!

Interesting that the pullup on the underneath is not needed on the flip flop - perhaps DJD just misunderstood when he drew his circuit showing R5 going to the wrong pin.

I assume the input must float high as it is a CMOS device - maybe a different result on LS - I will remove mine and test when I get five minutes. I have still not tested a 47K resistor yet - life has been a bit busy.
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Old Today, 2:40 pm   #374
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Default Re: Recreating the Bywood Scrumpi

tim
I just sent you the tim/phil pcb's.:pouces vers le haut:
The holes are big enough for the SPDT switch.:pouces vers le haut:
easy to find on our favourite sites.
I have tested everything as a bywood 47k 10 µf version etc.: rire2:
D rocker etc. everything works wonderfully
think about making a power supply in the style of mine 2x12V 10VA
7805 TO3 7912 -12v and lm337 -7v I may add the -9v to it.:idée:
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Old Today, 2:41 pm   #375
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see
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