Recreating the Bywood Scrumpi

[Slothie]

Originally Posted by Karen O

Were 'turned pin' IC sockets available mid-70s?

I can't remember

Only the best for my Scrumpi

Apparently they are!

[Karen O]

Well researched!

[Mark1960]

I find that turned pin sockets give a much tighter grip on the IC pins than the folded contact type for the first couple of insertions, but after three or four goes they start to loosen up to the point of being no more reliable than the folded contact type. BITD building custom label printers we would often use turned pin sockets and still tie the component down to the socket with nylon cord or tie wraps.

For rarer parts such as the sc/mp I or II, I’m a little concerned that the tighter grip of the socket might stress the component pins. Particularly if the IC is used in a few different iterations of a design where fitted to a new socket two or three times.

[Karen O]

Oh well, maybe the folded spring-type sockets will give a more homebrew feel to the project.

Did the original Scrumpi really call for LEDs with integral resistors? Maybe the design used the output resistance of the driver chips to establish LED current? (much teaching of grandma to suck eggs here, probably).

[Slothie]

The original didn't, the consensus seems to be that the inherent current limiting of the output stage was used, given that 70s LEDs were nowhere near as bright as modern ones and probably had a higher internal resistance anyway, I guessed this was necessary or at least acceptable. Tim and Phil seem to feel that the SCRUMPI used 74C04 hex inverters; I have not been able to find a data sheet that details the equivalent output circuit for these devices or the sink current, so it seems prudent to use some kind of series resistance for the LEDs with modern devices. When I get access to my electronic stuff I might experiment with direct driving LEDs with 74C04s and see how much magic smoke I can liberate!

[Karen O]

I constantly struggle to remember what logic families were available in the late 1970s. 4000 series CMOS sounds an unlikely contender for LED drivers (too weak) so, yeah, 74C04 (assuming they were available at that time). You can still get insensitive LEDs - I once bought a LED assortment from Velleman and they require 10mA to light adequately.

What about LS TTL? ISTR that these can sink 8mA.

[SiriusHardware]

Some of the original ICs in my MK14 are LS types so I think they are historically acceptable for 1978 at least.

[Timbucus]

From the SCRUMPI assembly instructions that Mike supplied it is confirmed that the driver was 74C04 and I haven't been been able to locate a data sheet for it either. JMK also says in the article for Microelectronics Reliability that he chose the CMOS part as it was able to source the current for the LED.

I think I mentioned above that I accidentally used some different LED's when I soldered in line resistors on my first PCB machine and they were really dim so I put the last two in without resistors on A1 and A0 and they have not burned out as yet and neither has the driver. I keep meaning to actually desolder the lead and take some current measurements as my measured test on the breadboard version when I was trying to decide the chips - values elsewhere in the thread - were up around the 58mA which is why I used resistors. Main problem is I have no idea where those specific LED's came from as almost everything else I have is ultra bright.

So to be accurate no, the LED's should not have resistance we just need the correct ones and truly know the chip specifications - he possibly allowed it to exceed by a margin but, how much we may never know.

I used the LS ones in my Prototype but, included the resistors as the LS04 would have its specified current exceeded by nearly three times on all six gates - seemed too big a risk.

[Karen O]

Tim, thanks for filling me in on the history and research into the choice of driver IC. I personally would run with the originally used part, even if I did have to replace them every 2000 miles

We have it easy with modern LEDs, don't we.

[Slothie]

You could always use warm white candle flicker LEDs for a real vintage feel!

[Karen O]

Or,

Colour changing mood LEDs. Plus a trough for burning incense sticks. Plus pre-recorded 'Awm' chant. Well the great man did say that Scrumpi was good for you

[Timbucus]

I quite fancy a polished wooden box now with a Nixi tube MK14 display on top, old typewriter style keypad and using a SCRUMPI as a single step / front panel display with traditional bulbs - the ultimate cyberpunk creation...

Of course the flags would have to be real Morris minor style pop out indicators.

[philoupat83]

Hello
to answer the LED question.
the best is to use the leds with internal resistor that i ordered in germany from https://www.reichelt.com/. my scrumpi works very well with
see the wire above. I join the data of the 74c04 in NS effectively BYWOOD in that PUB sells c04 and not LS04 (existed there in 1976?) the precise data 8mA under 10v (yes C thus CMOS power supply up to 15v) one can admit that under 5V 16 mA remains resonable.
I notice that you have fun with scrumpi.
I think about scrumpi 2 (JIM is absent)
and to scrumpi 3 a most difficult challenge but not impossible for many we can do it.

Translated with www.DeepL.com/Translator (free version)

[Karen O]

Could I ask: is there a parts list for Phil's new Scrumpi 1 board?

[Timbucus]

Yes it is in my booklet but, repeated here for convenience - the only slight change you may wish to make to have the original exact parts list is to swap our R4 to be a 47K and C1 becomes a 10uF - although the 4.7k/100uF works fine. If you find that the stepping is poor then a 4.7K pullup under the board on Pin 3 of the 555 to 5v may be needed when using CMOS parts.

Parts List
PCB Board epoxy 5 1/2” x 6" (this size was due to the original advert, in reality it was 5”x6 1/2”)
Integrated Circuits
IC1 ISP-8A/500D - 40 Pin SC/MP PMOS MPU (NOT INS8050)
IC2 74C00 - 14 Pin 4 CMOS NAND (Can be LS)
IC3 74C74 - 14 Pin Twin D Type Flip Flop (Can be LS)
IC4 NE555 - 8 Pin Timer (Slow and Step clock)
IC5/IC6 MM2112/AM9112 - 16 Pin 256x4 Static RAM
IC7/IC8/IC9/IC10 74C04 - 6 CMOS NOT gates for LED (Can be LS)
IC11 74C00 - 14 Pin CMOS NAND (Can be LS)
IC12/IC13 74C173 - 16 Pin 4 bit latches (can be wired as in or out)
(these two chips are optional extras, although originally supplied, and not needed to get the machine working)

DIL Sockets for all the above
1 x 40 Pin 4 x 16 Pin 7 x 14 Pin 1 x 8 Pin

LED
22 LED 5mm Red Address, Data,and Flag 1/2
1 LED 5mm Yellow (Flag 0)
1 LED 5mm Green (SIO)
(All LEDs need built in resistance to avoid excessive current drain on 74C04 otherwise 330ohm in series with +ve leg)

Resistors
R1 4.7K BREQ pullup
R2 4.7K pullup PROTECT/LOAD
R3 4.7K NE555 (R4 and R3 were reversed label wise on the real board)
R4 4.7K NE555 (this was 47K and called R5 on the original board, needs C1=10uF)
R5 4.7K pullup 74C74 D (this was actually used to pullup the 555 Pin 3 Pulse and called R3)
R6 4.7K pullup NWDS
R7 4.7K pullup NRDS
R8 4.7K pullup RUN/HALT
R9 4.7K pullup SA
R10 4.7K pullup SB
R11 4.7K pullup RESET
(The real SunMoonStars board had a resistor underneath to do the 74C74 D pullup, our R5 – a later fix perhaps. In tests it does not seem to matter that the 555 pin 3 with an LS does not have a pullup – if you need one with the C which theory says it should for reliable pulses then it can be soldered below)

Capacitors
C1 100uF NE555 (it has since been shown this was originally 10uF – see above comment)
C2 100nF decouplage/decoupler
C3 100nF decouplage/decoupler
C4 470pF (500pF NS) FRQ µP (or replace with quartz crystal of 1MHZ for more accurate timing applications)

Switches
11 SWITCH 1c2p (one common two position) - 8xDATA, SLOW, PROTECT, SA, SB
1 SWITCH 1c3p (one common three position) RUN/HALT
2 SWITCH 1c2p(m) (one common two position - momentary action) - STEP, RESET and LOAD
It is possible to use a three position momentary action for these - the one position remains unused.

21 Wire Links (traditionally in a mix of bare wire and white insulated).
L1 GND near 555 (Bare)
L2 W from Pin 1 NWDS on IC1 to Pin 2 on IC11 74LS00
L3 R from Pin 2 NRDS on IC1 to Pin 1 on IC11 74LS00
L4 Short link on IC1 linking SOUT to bus tracks to Buffers close to end of L21
L5 CE from between CPU and IC6 (BOTTOM RAM CHIP) to IC11 Pin 8
L6 A11 (marked as A12 sic) to IC11 Pin 12 (also linked to Pin 4)
L7-10 D4-D7 Bus to IC6 (BOTTOM RAM CHIP)
L11 5V Strap from power feed to IC6 (TOP RAM) Pin 18 (connected via PCB to IC5 RAM) (Bare)
L12-15 D0-D3 Bus to IC5 (TOP RAM CHIP)
L16 Near Pin 13 of IC11 to R/W on IC6 RAM (connected via PCB to IC5 RAM) for PROTECT and LOAD switches
L17 GND link between IC7 and IC8 (Bare)
L18 GND link between IC8 and IC9 (Bare)
L19 GND link between IC9 and IC10 (Bare)
L20 GND Link to right side of board near C3 (Bare)
L21 Bottom of IC1 linking FLAG0 to near FLAG1 and 2

[Timbucus]

The switches need to be PCB through hole parts not the solder tag panel mount variety...

[Karen O]

Thanks Tim.

[Slothie]

The totals for the switches are wrong; it's 12x1c2p and 3x1c2p(m) making a grand total of 16 switches.

[Timbucus]

Oops just noticed a two typos you need twelve ON/ON and three ON-(ON) momentary

[Timbucus]

That was creepy timing for us two Slothie! I just built my board and was following the instructions - this is the second time and I didn't notice it the first time.