Archive for January, 2012

Apple 1 Cassette Interface Update

Monday, January 30th, 2012

I have come to the conclusion that 74LS74 performs slightly better than the 7474 in the ACI output flip flop application. This is because of a slightly higher output voltage level in the LS series part. As noted in the past, the 7474 is slightly less subject to the potential floating input problem than the 74LS74. However, I have been exclusively using a 74LS74 on my own ACI without difficulty for a long time, so I think the floating input issue is more of a theoretical issue than an actual problem. However, I would verify any tapes you make before declaring your program or data is backed up.

Because of this change in thinking, I will no longer be providing the alternate 7474 ICs with my ACI kits.

Scopewriter Fail – reason

Saturday, January 28th, 2012

First of all – what is a Scopewriter? It was a circuit intended to make use of an oscilloscope for a single line terminal display. It can take 6 bit ASCII character input and display up to 32 characters on an Oscilloscope. The complete design, with PCB layout, was published in Popular Electronics in 1974.

Radio Electronics cover

Radio Electronics cover

I got interested in building one, thinking it would make a nice accessory for the Scelbi Mini-computer replica that I am planning on building. It is supposed to support a single line/32 character display. There is some documentation available, showing how to interface a Scelbi to a Scopewriter. I thought it also might make a nice display at VCF east.

So, using the PCB layout in the magazine I etched a PCB and acquired parts. Most parts were easily obtainable. However, the TMS2501, TMS3112 and the 1N750A zener diodes were hard to find. Eventually I found a TMS3112 in the UK. I tried buying a TMS2501 on ebay, but it turned out to be out of stock. Finally, I figured out that I could substitue a GI 2513 for the TMS2501 with some rewiring. I did a cross reference of the 1N750A zener diode and decided that a 1N5230 should work in place of it.

Next, I built it up and connected a PS/2 keyboard. So far, so good.

Scopewriter PCB

Scopewriter PCB

The problems started with the first debug session. I powered it up and connected the scope, hoping I would get lucky and get to see a line of characters, but nothing intelligible could be deciphered. After mucking around for a few hours, I found some mistakes in the 2513 wiring that I had hacked together to make the GI part work in this circuit. I fixed that and when the display didn’t improve and I called it a night.

Next debug session, I found that the 3 bit counter selecting the row on the 2513 didn’t look right, but couldn’t figure out the reason. I also noticed that the power supply design, wasn’t the best in the world, with a .5 volt 60 HZ wave showing on the +5 volt line. I did figure out that I had my keyboard adapter wired wrong and fixed that. At this point I could see that characters were being entered into the shift register correctly, but I still didn’t see a good display. After some hours of probing with an oscilloscope, I figured out that the GI 2513 character ROM addressing was different from the TMS2513 and that the bottom line of each character would be truncated when using the GI part. I decided that I could live with that for now. At this point, I was pretty frustrated, by continual problems, on what I originally thought, would be a simple project. I put the Scopewriter aside for a couple of months.

Scopewriter setup

Scopewriter setup

Last night I took it out again and figured out that the counter feeding row select to the 2513, worked better, if I changed a resistor in the the source clock generation circuit. Finally, if I put the same character in every position in the shift register, I could see the display of something approximating characters. Certain characters like “F” were easier to identify than others. However the display was only about 18 characters wide, unless I slowed down the scope to the point where the phosper wouldn’t persist for an entire sweep. Unfortunately, at that slow sweep speed, the display becomes unreadable.. Also the output was not stable, which I attributed to the unstable +5 volt supply.

Scopewriter Display

Scopewriter Display

The display of “F”s in this image actually looks a little worse than the actual display because the camera caught several scans in this single image.

Anyway, when I about wrapped things up last night, something broke in the power suppy, which is the point at which I stopped and sent my last nights blog entry and decided that this project would require several mods in order to work well.

  • base clock speed would have to be increased
  • the clock timing circuit resistor change needed reviewing
  • power supply would have to be improved
  • the 2513 addressing would have to changed make the bottom line visable
  • whatever broke, would have to be repaired
  • This morning, in order to take the pictures for the blog, I found the problem with the power supply. It turned out to be the 1N5230 zerner that had failed. I have a nagging fear that this substitute zerner is the root of many of my problems, so I’ll review specs again. I replaced the zener and took the pictures of the display for this blog entry.

    This has been one of the most stubborn, problem filled retro projects that I have ever worked on – hence the FAIL message. I’m going to put this project away again – maybe I’ll pick it up again some day.

    Scopewriter Fail :-(

    Friday, January 27th, 2012

    details later

    The Ultimate Replica 1?

    Friday, January 27th, 2012

    See what can be done with Vince Briel’s replica 1 and one of my Apple Cassette Interface cards. Check out this entry on Vince’s forum.

    “Retro 1” Systems

    Friday, January 27th, 2012

    Marty Ewer is now selling “Retro 1” systems on ebay for $249. They are fully tested Apple IIe computers equiped with my Brain Board. If you are looking for the easiest, least expensive way to an authentic Apple 1 experience, this may be it. In addition, you get a working Apple IIe in the bargain. Search for “Retro 1” under user “shockwavetechnologies” on ebay.

    Remarkable Apple 1 and Documents Revealed

    Friday, January 27th, 2012

    Check out my Apple 1 registry for the newest entry. The most remarkable part of this entry is the letter from Steve Jobs about a possible exchange for an Apple II.

    Letter from Steve Jobs

    Letter from Steve Jobs

    Note that a 4K Apple II board at the time retailed for $598.

    Search for Fred on this page for more information about this Apple 1.

    Aging of Ceramic Capacitors

    Thursday, January 26th, 2012

    Many people restoring vintage electronics items are concerned about old electrolytic capacitors. Little is said about vintage ceramic capacitors, but some types of ceramic capacitors age, and can lose a considerable amount of their capacity over time. The interesting thing is that they can be restored by a simple heating process. Check out this web page for more information.

    The “Harvest of Death” photo

    Monday, January 16th, 2012

    Excuse the morbid curiosity exhibited in this post. I debated whether to post or not, and in the end, decided to do so.

    Most days, I’ve taken the time to view the latest entry in the “Gettysburg Daily” blog. Recently Jerry Coates did a report on his assertion about where the “Harvest of Death” photos were taken, as William Frassanito could not find the location of these photo’s. I’m pretty well convinced by Jerry Coate’s argument, that the pictures are of the 5th New Jersey near the Spangler farm.

    The image, can be found on the Library of Congress website.

    I’ve always been struck by the fact that this photo seems to depict the dead as they fell in a line of battle, not as a row of dead lined up to be buried.

    harvest of death

    There is another article by Coates describing his line of thinking at:

    In that article, Jerry lists the name and companies of the 13 soldiers of the 5th New Jersey that were killed on the second day at Gettysburg. I’m reordering that list here by company.

    Lt. Henry R. Clark, Company A
    Pvt. Patrick Tynan, Company A
    Pvt. Samuel W. Bradford, Company A
    Cpl. Edgar S. Van Winkle, Company B
    Pvt. Ananias Lynn, Company B
    Pvt. John Ryan, Company C
    Pvt. Heinrich Troch, Company E
    First Sgt. Theodore Sutphin, Company F
    Pvt. John 0. Heath, Company G
    Pvt. John H. Johnson, Company H
    Pvt. Samuel Hasselman, Company H
    Lt. Thomas Kelly, Company I
    Pvt. Edward Martin, Company I
    Pvt. John Ensch, Company K

    Regiments in the Civil War were deployed in lines with soldiers touching shoulders with each other. This is normally estimated as a spacing of about 28 inches frontage per soldier. The usual deployment of a regiment was 2 lines. In this battle, the 5th New Jersey deployed as a single line to cover all the ground they were assigned. Apparently the left end was turned back or in military parlance, refused. With 206 enlisted men and about 28 inches per soldier, they should have covered about 160 yards of frontage (28/36 x 206 = 160). That would be an average of 16 yards or 48 feet per company. The 10 companies of a regiment normally deployed with Company A on the right, proceeding to Company K on the left. There is no Company J in the 5th New Jersey. There is no evidence that the 5th New Jersey would have deviated from this standard deployment of companies at Gettysburg.

    If we assume killed in action died close to where they were hit and have not been moved prior to the photo, there should be a distribution of bodies similar to this chart. Company A, being closer to the Camera, and Company K being in the distance.

    KIA per company

    KIA per company

    According to Coates theory, this “Harvest of Death” photo looks southward from near the Spangler farm, along the line of the 5th New Jersey.

    So we are probably looking down the line of battle, starting at company A, then B and so on. Note how the distribution of bodies in the image is similar to the distribution of killed in the various companies. A bunch of bodies are near the camera, where companies A and B suffered the most KIA of the regiment. Then there is a relative lack of bodies where the center companies were in line. It is hard to make out the distant bodies clearly, but it is possible that there are more bodies there, than in the center of the line. Also, you can see the debris that shows where the left of the regiment was refused.

    I do have a question though. It just doesn’t seem like the line extends for 160 yards in this image. Is this due to a telephoto type lens fore-shortening the image, or was the line of the 5th New Jersey shorter than simple math would expect? If the characteristics of O’Sullivans camera lens is investigated, maybe the answer could be provided.

    If all the assumptions are correct, then the nearest bodies are those of company A, B and possibly C. If you use your imagination, no men are visible where company D was positioned and the single KIA of companies E, F and possibly G alone in the mid-distance. Could they be the bodies of Pvt. Heinrich Troch (company E), First Sgt. Theodore Sutphin (company F) and Pvt. John 0. Heath (company G)?

    Since we know the dead in each of these companies, a person could try to find carte de visites of the slain soldiers of companies A, B and C, and possibly try to identify those bodies.

    If all these assumptions are true, it also indicates that KIA in the Civil War, means just that. Soldiers killed in action would have died very close to where they were hit. Though the image is only sharp in the foreground, I can be reasonably sure that 8 bodies are in view. It appears that several more might be in the haze in the background, others buried already, and one unfortunate soldier might be barely showing on the left side of the image. It could be that almost all 14 of the KIA of the 5th New Jersey are in this photo. If any Confederates were killed in this area, they would have been buried before the photo was taken, while the Confederates still occupied this ground.

    Also keep in mind that the 5th New Jersey suffered 60 wounded soldiers during the battle, most of whom were probably wounded at this location. It is sobering to to think of the horror that the men of this regiment experienced, during this engagement.

    Apple 1 trivia question

    Thursday, January 12th, 2012

    Be sure to make an effort to visit the Vintage Computer Festival East in May:

    Now the trivia question.

    What is the address in the silicon valley where Apple 1s were built?

    To be answered in this blog in the future – post your answers in the comments section.