Planning a build of the Acorn System 1

[linker3000]

Not very exciting project update:

• Won some 1970s era (NOS) Vero and Roadrunner Eurocard/DIP package prototyping boards on ebay for that extra-special authenticity; they were also about 1/3 the cost of buying the same boards new, albeit they'll probably need a bit of polishing!
• 1MHz crystals (2) ordered from a vendor in the USA at a good price. I'm over there shortly for company training so I've had them delivered to a colleague for pick-up.
• Going to rummage through some old stock in a silicon valley parts store for the RAM and ROMs. Ordering off ebay is just too easy!
• Looking for some 10x5mm rectangular tact switches that look like the originals. The ones on ebay/Aliexpress tend to be 6x3mm or round. Might not really matter once/if the switches are covered by a laminated overlay. (Any ideas here?)
• Might fork out for a PROM/EPROM programmer as I'll probably use it for more things later - looking at the TL866CS

[linker3000]

Well, as you might have guessed by now, this project is not exactly a rush job!

Best laid plans and all that - my trip to the USA was postponed so I have two 1MHz crystals sitting in San Jose that I won't be able to pick up until around September. Never mind, I bought a tray of 24 off a well-known auction site so I'll have what I need + some to resell (at a very good price!) in singles - so keep your eyes out if you're in need!

I took a punt on some tact switches for the keypad, but the dimensions turned out to be for the overall switch body and not the white button bit at the top so they are a bit tiny. Try try again....

All I have left to source is handful of glue logic (74xx/74LSxx stuff) and they seem to be lesser-used types, which means I do not have any already. Buying the chips in small quantities via a popular auction site seems to be a very expensive option. Farnell / Element14 has all that I need, but I will have to justify buying something else at the same time as their minimum order value is £20 and the logic chips come to less than £4.

The 2114 static RAM has arrived and so have the 74S571 bipolar PROMs; my other recent purchase - a TL866 programmer - won't blow them so I will have to knock something up using an Arduino - or program them a bit at a time via DIP switches.

Onwards (slowly)...

[Michael]

Hi Linker3000,

Which 74xx/74LSxx parts are you having trouble sourcing? Perhaps your stateside associate could help you with these, too?

Regards, Mike

Code: Select all

  CPU Board      Jameco  Mouser
-------------    ------  ------
IC9  74LS20       0.79    1.00
IC10 74LS139      0.69    0.86
IC11 74LS04       0.49    0.74
IC12 74LS00       0.45    1.20

 Front Panel     Jameco  Mouser
-------------    ------  ------
IC8  7445         2.49    2.96
IC8  74LS145      0.89    1.12  7445 alternative

[linker3000]

Michael wrote:

Hi Linker3000,

Which 74xx/74LSxx parts are you having trouble sourcing? Perhaps your stateside associate could help you with these, too?

Regards, Mike

Code: Select all

  CPU Board      Jameco  Mouser
-------------    ------  ------
IC9  74LS20       0.79    1.00
IC10 74LS139      0.69    0.86
IC11 74LS04       0.49    0.74
IC12 74LS00       0.45    1.20

 Front Panel     Jameco  Mouser
-------------    ------  ------
IC8  7445         2.49    2.96
IC8  74LS145      0.89    1.12  7445 alternative

Yes I priced up an order at Jameco, but my trip to the USA has been rescheduled for Sept/Oct, which is stretching things a bit far - even for my relaxed timeframes! Postage to the UK was pretty high so I decided to order from Farnell/Element14 and bump the order up to £20.

I just need to sort out the keypad buttons now.

[linker3000]

It turned out that the prototyping Eurocards I obtained aren't suitable for small (non 24/40-pin) DIP chips so I have decided to lay out some boards and I am currently entering the original Acorn schematics into KiCad. The aim is to have single sided versions of the originals so that they can be etched easily at home. This should also make it easier to lay out the keyboard. I'm going to replace the original inter-board Spectra Strip with a modern ribbon cable link + the display will be on header pins so I can replace it when wanted with a 0.5" 7 Segment LED alternative. I'll publish the designs in due course.

I have all the bits now!

[Michael]

Sorry to hear the Eurocards didn't work out.

I think the display header is a good idea...

Good luck... Cheerful regards, Mike