Archive for the ‘8008’ Category

8B backplane and 4K SRAM Soldered

Monday, September 15th, 2014
8B backplane and 4K sram

8B backplane and 4K sram

I found a small issue in the layout of the 4K SRAM card. The trace leading from the ground past the fuse holders passes too close to the fuse holder for comfort. Since there is no solder mask on these boards, it would be best to mask this trace at this point with tape or something so it can’t inadvertently touch the fuse holder and short +5 to ground. Reviewing my layout, it looks like I missed aligning this trace correctly to the original layout. The layout in this area was obscured by the 10uF capacitor, and I didn’t notice the difference when comparing my layout to the original.

Ground Fuse Holder Issue

Ground Fuse Holder Issue

Next board to solder is the memory expansion board. It it will be fun putting in the 67 resistors that populate that board. Then I’ll have to cobble together a chassis for testing.

Apple 1 Registy updated and new SCELBI registry

Sunday, September 14th, 2014

I just posted an update to the Apple 1 registry. One system was deleted and one added, so the total count holds at 63. The new one is John Anderson’s, which will be sold at auction, next month. I just was contacted by the owner of what is probably an unlisted system, so the count could grow to 64, very soon. Christopher’s system, which has been shown at K’Fest, VCF midwest and VCF east has been undergoing some restoration, so I added an updated image and additional information.

Note that the success of the Apple 1 registry is largely due to contributions of owners and former owners and other interested parties and I greatly appreciate all new information.

What’s really exiting to me is the new SCELBI registry. If you think Apple 1’s are rare, I could only find information on 13 SCELBIs. I recently received information on what could be a 14th, but it also possibly could be the missing Freeman Museum unit. The images on the SCELBI registry will be a little different than the Apple 1 registry, as the images will emphasize the quirks and differences between the units. Many original SCELBIs don’t exactly look like factory stock systems, so Iit should be a good resource for people building reproductions.

I expect that some of the information may be incorrect. Bear with me as I expect to refine this registry quite a bit in the future.


Thursday, September 11th, 2014


The SCELBI 8B backplane, SRAM and memory expansion boards just arrived. They may take a couple of weeks or so to check out. If they work, I’ll be able to get floating point SCELBAL up and running on an 8B for the first time in a very long time, and so will you. There is a semi-reproduction that has run SCELBAL, so maybe not the first, but it all depends upon how you classify that system. To start with, I’m building a minimal, barebones, chassis mainly to allow check out of the SRAM and get SCELBAL running.

You will notice that there is a stack of cards involved. The big question is whether I finally screw up a layout and have to ditch one of these batches of cards. To date, I’ve never made a small prototype run of a few boards to check my work. There were prototype’s made of a few of my smaller cards, but they were either made on prototyping boards or etched here at home, where the cost is almost nil, compared to professionally made PCBs. The benefit of this rather risky approach is that I save a great amount of money by not making what would be rather expensive prototypes. This directly translates into a lower cost project for you and me. In addition to the risk of making a complete batch of dud cards, another downside is the great amount of time spent reviewing the layout before I eventually pull the trigger.

at last – PCBs for SRAM only SCELBI 8B are now on order

Wednesday, September 3rd, 2014

Some people have been asking for these for a couple of years – well I hope the wait will be worth it for those people.

I have also started serious work on the PROM card. Turns out that I will probably end up going over and tweaking the entire design that I started with, so it will take a little while. Not as long as doing the 3 other boards, but those that are interested will have to wait a little while longer for the PROM boards.

I’ll have the PCBs in a week or two, but I also need to order a few parts so that I can build them up and do some sanity testing.

Dover Mini-Maker Faire Experience

Monday, August 25th, 2014

Dover, NH Mini Maker Faire

Dover, NH Mini Maker Faire

Just sharing some experience from the Dover Mini Maker Faire which was Saturday. I had Micro – Chess going on the Mimeo and Dave Ahl’s HI-LO in tiny SCELBAL (integer BASIC) on the SCELBI. It was busy almost the whole day, just a few fairly brief periods between visitors. It seemed a bit busier than Saturday at VCF.

HI-LO was the perfect text game for casual visitors of all ages – simple to teach and quick and easy to play – I was impressed by the number of small kids that immediately proceeded to use a binary search algorythm to find the number.

A lot of people tried a few moves on chess, but the user interface is so awful on the Apple 1 port of micro-chess – I had to train almost everyone – even though I had instructions posted.

I met an original Mark-8 owner(still has his system). That guy added a digital group video card to his Mark-8 and made some improvements to it, which were used by later generation Digital Group video cards. Another person who was into SWTPCs in the day. Another person that was once vice president of the Boston Computer Society. And finally, another guy who worked with Draper Labs on the Apollo guidance system computer.

There was a wide variety of exhibits from art and crafts to a young man who was building a neutron generator. If you have a mini-maker faire in your area, I’d say it would be worthwhile to show off your gear – you might meet some interesting people.

List of all SCELBI PCBs

Wednesday, August 20th, 2014

I plan to reproduce all the SCELBI PCBs. There are 16 types of boards in all. The 1106-1108 8B boards are practically ready to be made. I’ll probably tell the PCB factory to start on them this week. This will mean that in a few weeks I’ll have 10 of the the 16 boards done. The really good news is that most of the remaining cards are only single width, so reproducing them should go much faster than the double width system cards.

Here is the complete list of the PCBs that SCELBI Computer Consulting made and my reproduction status. The peripheral cards are listed in my most likely order of reproducing them

Main System Cards
1100 CPU – 8H/8B
1101 Data bus buffer – 8H/8B
1102 Input – 8H/8B
1103 Backplane – 8H
1104 Front Panel – 8H/8B
1105 1K SRAM – 8H

In progress
1106 Memory Expansion – 8B
1107 4K SRAM – 8B
1108 Backplane – 8B
1109 PROM – 8B

Peripheral Cards
2104 Teletype interface*

Not started
2105 Keyboard
2100 Oscilloscope digital**
2101 Oscilloscope analog
2102 Audio Tape output
2103 Audio Tape read

* not as high as normal vector boards
** double width vector board

SCELBI 8B update

Monday, August 11th, 2014

Hi SCELBI fans,

Based on scarcity of reports, it may not seem like it, but I am still actively working on the SCELBI 8B card set. It is pretty tedious work, and reporting every new set of tweaks to the layout is not very exciting, so I haven’t been reporting ongoing progress.

To be honest, I prefer exploring new projects, rather than revisiting old ones. Though the SCELBI 8B is “new”, it leverages so much of the 8H design, that it really seems more like revisiting the 8H, than doing something new.

At this moment, I am going through final design checks of the SCELBI 8B backplane, memory expansion, and 4K SRAM PCB layouts. I already have quotes and have done DFM checks with my PCB supplier. I think I will probably build up an very basic 8B system without I/O in a temporary chassis in order to get these cards checked out. This is so I can offer the PCBs for sale for those of you who can’t wait for the whole package. Based on what I know at the moment, I might be ordering PCBs in as little as a week or two from now.

The chassis sheet metal and the EPROM card will come a little later as follow on efforts.

After that, my next efforts will probably be the SCELBI keyboard and oscilloscope interfaces. Those will be “new” to me, so will be a lot more fun to do than the 8B has been. The O-scope interface poses some interesting challenges, as we don’t have any original software for it. We will have to craft some drivers using only the hardware implementation as a reference.

More Vintage Fonts – The SCELBI Front Panel Logo

Thursday, July 17th, 2014

For a while I’ve had an interest in vintage typefaces. This interest stems from my efforts to reproduce vintage literature and the logos.

When I made my SCELBI front panels, one of the challenges I had, was to match the font for the SCELBI logo. Here is an image of the overall front panel.

SCELBI front panels

SCELBI front panel

and a close up of the logo.

Scelbi logo- close up

Scelbi logo- close up

Even though this is a variant of the omnipresent Helvetica, finding a digital font to match was harder than you think. After searching through dozens of variations of Helvetica and derivative fonts, in the end, I choose to use the very similar Helvetica Black. In some cases in the past, I have used Adobe Illustrator to manually recreate logos and such, but recreating characters accurately is extremely difficult and it is vastly easier to use off the shelf fonts.

Scelbi Logo in Helvetica black font

Scelbi Logo in Helvetica black font

It’s a pretty close match, but in reality the original logo’s characters are just a bit wider, so it’s not perfect.

I’ve known for a while that the single largest source of typefaces for printers and advertising people back in those days was Letraset brand rub on transfers. Back in the day, anyone that had anything to do with the printed word, would have had a Letraset reference manual, which contains hundreds of fonts and other visual goodies. Vintage Letraset manuals are available from used book sellers and even on ebay. Recently I picked up a 1981 edition.

Letraset Reference

Letraset Reference

One the first things I did when I got this guide was to determine if I could find an exact match for the SCELBI front panel logo. Here is what I found on the page with bold type Helvetica fonts.

Letraset Helvetica Bold

Letraset Helvetica Bold

If you ask me, plain old Letraset Helvetica Bold is an exact match and was the source for the lettering on the original panels. Now I’m just going to have to figure out the best way to digitize and scale the example letters found in the Letraset guide for my next batch of front panels.

SCELBI 8B update

Friday, July 4th, 2014

Here is a composite image showing the great progress that has been made on the 4 boards that need to be done for the SCELBI 8B.

Composite Image of 8B Boards

Composite Image of 8B Boards

Still a ton of tweaking and fine tuning needs to happen, but you can almost see the light at the end of the tunnel. I also need to find some time to figure out what I’m going to do for the custom chassis.

The backplane layout is for all intents and purposes done. The memory expansion card is next closest to complete. I haven’t done much with the PROM card, but I’ll do a complete review of it. The curved traces promise to require a lot of effort to match up to the original. The 4KSRAM cards need a lot of work and since the original has curved traces, it will take an extra effort to finish.

I’ll be at the MakerFaire in Dover, NH Aug, 23rd

Tuesday, July 1st, 2014

I’ll have a Mimeo (Apple 1 clone) and a SCELBI 8H clone up and running and if you come, you’ll be able to see and operate them.

MakerFaire Dover Flyer

I hope to see you there.