This document provides rework instructions that will bring the PCB up to the revision seen in the schematics. I now have a pretty good understanding of how this interfaces works and will provide more details in a future post.
Over the last few years, we have had a plague of small moths, especially in the spring time. There are so many, that the larva from these moths defoliate certain types of trees in the spring. So far, these trees have managed to survive, but I’m wondering how many more years that they will be able to tolerate this. The moths are attacted to the lights inside the house at night. There are so many moths, that they get into the house almost every time you open a door at night.
While discussing the disapperance of the Bats with a neighbor the other day, I think I came up with the likely reason that the moth population has run amok. Bats eat moths and other similar sized flying insects, such as dragonflys. With the bats out of the picture, the moths have had little to curb their population, except the available food supply.
Note that bats typically do not eat mosquitos, since mosquitos are too small too provide much nourishment. Dragonflys do eat mosquitos, so with the bats gone, there may also be a reduction in the mosquito population as one consumer of the dragonfly population has been taken out of the picture. Come to think of it, the mosquito population does seems to be low for this time of year.
The balance of nature sure is sensitive and it’s surprising to see it out of whack in our own backyard.
This is an image of the current state of the back sidelayout of the long awaited (by a few) digital board overlaid over an image of the actual board. Base image is curtesy of Jack Rubin, the only person I know, that has seen an SCELBI oscilloscope up close and personal in recent memory. This one is in the Computer History Museum’s off site storage facility.
I haven’t worked on any of the lettering, but I’ve gone through multiple passes of the rest of the board. Based on file size, this board is actually more complex than the SCELBI CPU board.
One other thing that I’m going to do is more study of the rework on the only known Oscilloscope digital board. The arrows in the image point to areas where rework was applied. Initial review seems to indicate that the schematics found at scelbi.com match the board after rework was applied. There is also a bit of rework on the front side.
The analog and keyboard layouts are ready to go, though I’ll probably give each of those one more quick design review pass before ordering a batch.
Link to SCELBI’s app on Apple’s App Store This is the same version (2.7) as available for download from my SCELBI web page. If you have used this version it would be great if you would review this Application on Apple’s App Store.
I now have a batch of Brain Board kits ready to go.
For kits sent to the US – send $59 per kit to my Paypal account (at end of this email)
For kits sent internationally – send $59 per kit, plus $10 postage (combined shipping for all kits) to my Paypal address (at end of this email)
For those that want to build and test the kits add $25 per kit built and tested.
Shipment should occur within a few days, except for those that want me to build and test – expect a week or so before shipment.
My PayPal address is: (firstname.lastname@example.org)
Make sure you include your shipping address with Payment.
thanks and best regards,
I now have everything that I normally stock on hand – except SCELBI front panels.
I was a bit behind on things, but today I shipped a few items that I owed people, so am caught up, with the exception of those SCELBI front panels.
In addition, due to popular demand, I made a new run of Brain Board kits. I tested an example earlier in the week, and except for a bad 74LS74 IC, I found they work fine. I’ll have to go through my stock of 74LS74’s and test them before finishing putting together kits. With luck, I’ll have kits ready to ship by next weekend. Watch for an update in the next few days before sending money.
A month or so, ago, Bernie Kempkinski, made a post in the Yahoo, Civil War Railroad’s and Modeling group. This post had links to images of actual train reports from the City Point and Army Line Railroad during March and early April, 1865. Train reports list the times that trains passed the various stations on the line. Presumably the stations telegraphed trains movements back to City Point as they occurred. Bernie had found these reports in the National Archives.
The dates of the reports that Bernie found, coincide with the final days of the siege of Petersburg and include March 25th, 1865, the day of the battle of Fort Steadman, and Abraham Lincoln’s visit to the front lines at Petersburg. Having a great interest in what was going during those days at City Point and Petersburg, I had previously purchased a book by Donald Pfanz, “Abraham Lincoln at City Point”. This books details Lincoln’s day by day activities during his time at City Point and vicinity during March and early April, 1865.
Of course the first thing I had to do, was to see if the train Lincoln took to see the front on March 25th, was listed in the train report for that day. Pfanz’s book reports that the Lincoln party took a train at around noon. Sure enough, in the report there is a special train arriving at Pitkin Station, the next station up the line from City Point at 12:30 – that must have been Lincoln’s train.
However this is where things get interesting. Pfanz writes that the Lincoln party went to Patrick Station, and then mounted horses and ambulances to visit Meade’s HQ. Pfanz writes that they arrived at Meades HQ around 1:00PM. He goes on to write that the party viewed a number of Confederate prisoners from the battle, then went to Fort Wadsworth to see the Sixth Corp take some advanced works in front of Boydon Plank Road.
This story hardly could be the truth. Patrick Station is a mile beyond Warren Station, and Fort Wadsworth is between these two, and all are several miles down the track from Fort Stedman and Meade Station, which I presume was close to Meade’s HQ. The special train arrived at Warren Station at 2:00PM, long after Lincoln is said to have visited Meade’s HQ.
I think it is more likely that the Lincoln party changed to ambulance and horse at Meade’s station, viewing the killed, wounded and prisoners from the battle of Fort Stedman near that location. Then they road down the line to Fort Wadsworth, from which they viewed the attack of the Sixth Corps. Afterward, they could have reboarded the train at Patrick Station for the return trip to City Point.
Here is an image of a SCELBI analog board. Overlaid on top is my current front copper layout and a silk screen layer showing component mix. As you can see, the layout is very far along, considering that I’ve only worked on it for parts of two weekends. There is still plenty of tweaking and checking to be done, but there is good chance that the layout, as it stands, would work.
Note that this board has several component locations without components stuffed and a couple of 56K resistors tacked on. There are no pads for these resistors, but they show up in the schematics and on the SCELBI placement diagram. I wonder if there was a second batch of cards made with corrections?
The 130 ohm resistors are listed as 100 ohms in the schematic. It would be hard to know why there was a difference without doing some experiments on actual hardware or a circuit analysis. This change could be functional in nature or do to using components that were close enough and on hand. The 3K resistors are listed as 3.3K in the schematics, but I think they used what was on hand, and there probably isn’t a functional difference in that case.
The pads in the lower left are for decoupling capacitors. I don’t know why they weren’t stuffed in this example. The component mix is pretty basic. There appear to be some film and mica capacitors. Based on what I’ve seen on other SCELBI boards, the transistors are probably 2n2222 and 2n2907 types, but I don’t have confirmation on that. Probably the most expensive parts to source are those pesky 72741 op-amps in 14 pin packages. They seem to be available on eBay, but the asking price is very high. I’m going to be on the lookout for a better source.
One final thing that threw me for a loop on this board. When compared to all other SCELBI boards, the DIP packages are mounted upside down. I’m going to have to pay attention when assembling this board.
A few days ago, I was searching through my small personal archive of Apple II floppy disk images, looking for an Apple II clone of Colosal Cave. As fate would have it, among those images, I ran across a program called “THEGREATAMERICANPROB.MACHINE”. Vaguely recalling it being a fun program from the “old” days, I started up an Apple II emulator, loaded the DSK image and ran the program. Here is a screen capture
and a movie of the program in action.
Just as I sort of remembered, it was a pretty cute Apple II low res color graphic animation. However, when the credits rolled, I discovered something totally unexpected. It was written by none other than Bruce Tognazzini. Tog, as he is now known, is now a respected authority on user interface design.
Having had a brief email interaction with Tog a few years ago, and knowing he was quite approachable, I decided to send him a message. I let him know that this old work wasn’t forgotten. I figured that he would appreciate that. The response I recieved, had some quite unexpected news. Here is Tog’s reply.
Thanks. It was when Steve Jobs saw that program that he decided to hire me. It was the first ever full-screen animation done on the Apple II.
I sent him another message thanking him for his reply and asking him if he minded if I shared it on my blog. He responded with more details about how “THEGREATAMERICANPROBMACHINE” helped get him hired at Apple.
Not a problem. Specifically, I took a piece of code I’d written that added a new command to Integer BASIC down to Apple to show Steve. After selling him on that, he asked me what else I had done. I showed him the Probability Machine, throwing it up on Apple’s large-screen Advent projector. He got really excited, left the room, and gathered up everyone he could find in the building. (Apple was still all in a single building in those days.) I was quite surprised it caused so much excitement; I had no idea I’d pulled off something that, at the time, was a breakthrough. A week or so later, Jef Raskin called me up and said that Steve thought we should talk. I assumed he was going to want to buy some more of my software. It turned out, he and Steve wanted me,
Over the weekend, I started work on the SCELBI O’Scope PCB layout. There are two boards that make up the package, a standard size analog board, and a double width digital board. The standard size analog board looks like it will be pretty easy to layout. However the double width digital board looks pretty complicated. It has 35 chips, and around 220 VIAs. By comparison, the Apple II, rev 0, which has to be the most complex PCB that I have recreated has about 380 VIAs. The chip count is the second most for any SCELBI board. It trails behind the 4K SRAM board, which has 37, 32 of which are SRAM chips. All the SRAM chips on a SRAM board are connected the same way, which simplified things quite a bit on that board.
The good news is that, so far, I haven’t run across any components that will be excessively difficult to find.
Another complication on the digital board, is that I only have three good images of two different O’Scope boards. The front and back of one board, and the front view of a second. The board that I have front and back views of, has quite a bit of rework on it. I don’t know if these are design issues or customer modifications. It will be interesting to sort through these changes and see if there are any differences between these two boards.
The final challenge will be figuring out the details of the power supply that is integrated into the O’Scope chassis. At this point, all that I have to go on, is a picture. When you put everything together, the SCELBI O’Scope interface turns out to be far more complicated than many single board “trainer” type computers.
The keyboard interface layout is complete. I have done design checks and have a quote in hand. I probably will not order boards until the O’Scope layouts come together, or at least until they get further along. I think of the keyboard and O’Scope boards as kind of a matched set, the keyboard for input, and the O’Scope for display output. One, without the other is kind of a half solution, though I will be able to test them out independantly.