It's long overdue - Cosmac Elf II build

[rubber_jonnie]

More parts arrived!!!

IMG20260403090406.jpg (355.03 KiB) Viewed 1384 times

And installed:

IMG20260403092536.jpg (366.07 KiB) Viewed 1384 times

Well, all bar the .1uF caps, I'll do those later

I just need to see what ICs I have in stock and what I need to order, as there are a few 74C and 74HC parts that I'm confident I just won't have to hand.

[stephen_usher]

More fun!

I just need to see what ICs I have in stock and what I need to order, as there are a few 74C and 74HC parts that I'm confident I just won't have to hand.

The chip count doesn't seem that high. There must be come odd chips in there though to have too many cache misses on your chip store.

[rubber_jonnie]

More fun!

I just need to see what ICs I have in stock and what I need to order, as there are a few 74C and 74HC parts that I'm confident I just won't have to hand.

The chip count doesn't seem that high. There must be come odd chips in there though to have too many cache misses on your chip store.

Yep, definitely some weirdness, and a LOT of cache misses. Some seem to be quite old as it goes. Also we're looking at a CMOS CPU so that is likely why there are matching CMOS logic IC's.

I need:

1. A CDP1861 - this is for using a video display and is optional, though there are modern replacements.
2. A 74HC74.
3. 2x 4049's
4. A 4023
5. A 74HC573
6. 2x 4016's
7. 2x 9368
8. A 74C173
9. A 74C922
10. 2x 16 pin DIP 120Ω resistor packs. Looking at the schematics this would be easy enough to replace with individual 120Ω resistors.

It's all very original parts codes as far as I can tell so there may be newer equivalents for some, I'll check.

Time to solder in the rest of the decoupling caps.

EDIT - Decoupling caps are all done now

Looking through my parts drawer all I have from that list is a 74HCT74, which in theory as it's a 5v system I could use to replace the 74HC74.

The 40 series ICs are all still made, so that should be fine so I can order those, the others, specifically the 74C173 and the F9368 are proving harder to find.

[rubber_jonnie]

Whilst I'm at it I've ordered PCBs for this from JLCPCB:

AVI ELF II TIL311 6-Digit Display Card.jpeg (112.45 KiB) Viewed 1361 times

And this:

avi1861-rev-a-assembled.jpg (46.92 KiB) Viewed 1361 times

Which will give me an improved LED display and also a replacement for the CDP1861, which will also give me a video output

I have some TIL311 LEDs coming and it means that if I cant get one of the original LED driver ICs, and they aren't cheap, then I can install this LED board instead.

[HigashiJun]

Can't wait to see what the final result will be, ie. with its home made case.

[rubber_jonnie]

Can't wait to see what the final result will be, ie. with its home made case.

It's probably not going to have a case

I at least have all the parts coming now, somebody off another forum has sent me a pair of LED driver

[HigashiJun]

It's probably not going to have a case

Oh no ! A naked retro...

[rubber_jonnie]

It's probably not going to have a case

Oh no ! A naked retro...

TBH it's supposed to be naked:

Elf.png (2.5 MiB) Viewed 1330 times

Which is quite normal for this sort of machine. The Science of Cambridge MK14 I built is also case free.

Now the Atom I just built and the OSI C1PMF I bult a while back are supposed to have cases, but the jury is still out as to wether that will happen or not.

[HigashiJun]

TBH it's supposed to be naked:

Good to know that, but won't it be quite awkward ?

I thought your MK14 has a case too...

[rubber_jonnie]

TBH it's supposed to be naked:

Good to know that, but won't it be quite awkward ?

I thought your MK14 has a case too...

Well I am OK with it just being a PCB and it laying flat.

The MK14 was never intended to have a case AFAIK, but it does have feet