Archive for November, 2012

SCELBI quick update

Monday, November 26th, 2012

Just a quick update on SCELBI progress…

I have completed schematic layout comparisons of three of the five main 8H boards. What this means, is that I have compared the layout to the schematics and corrected any unexplainable differences between the two. This is a time consuming process, but I did find a few mistakes in my layout, so this has been worthwhile. I also found (for the second time) that there is one small mistake in the DBB board schematic. I also discovered that there were two versions of the DBB board made (I am laying out the later version) The boards I have completed this check on, are the front panel board, the CPU board and the DBB board. The CPU and DBB boards are fairly complex and took a while to do.

The remaining boards, input and 1K memory, are less complex and shouldn’t take quite so long. After these two boards are checked, I have to do some checking of pads and hole dimensions for discrete components. I learned some time ago that getting hole sizes right is as critical as any other single part of this process. After the dimension checks are complete, I have a final CAD check left to do, before getting quotes and the boards sent off to be made.

I also have done some work on the 8H backplane. The backplane is starting to shape up, but I’m not sure if I will have these built along with the five main cards or not, since with a SCELBI you can hardwire a backplane.


Wednesday, November 14th, 2012

I spent a couple of evenings taking another look at the SCOPEWRITER. Followers of my blog will remember that last spring, I declared the SCOPEWRITER project a failure. At that time I put it away, knowing that eventually I would make another attempt at getting it going. Well, I have good news, at this point, I can’t call it a failure, it might even be called a qualified success.

Here is an image of the output, that I was able to create.


I had to make two changes from where I left off, in order to get this output.

  • After entering characters, I had to disconnect the PS/2 keyboard that I had attached to it. The extra power draw of the PS/2 keyboard was too much for the power supply. As I use one of my PS/2 to ASCII adapters to get input to the SCOPEWRITER, I left the PS/2 adapter attached but unplugged the keyboard from the adapter. So I enter characters using the keyboard, then unplug it from the PS/2 to ASCII adapter. You can still see some 60HZ ripple on the output, but it’s not a showstopper.
  • I had two address lines feeding the 2513 Character generator swapped, causing characters to be displayed wrong. At some point, I’ll find a reaonable price on a TMS2501 and pull the jury rigged 2513, which has caused me so much difficulty during this project.
  • So now I have a working SCOPEWRITER. Come the think about it, this may be the only working SCOPEWRITER in the world. What else will I do with it – well at some point it will make a fun output device for the SCELBI 8H and I may just have to create a web page for it. And one other thing – my point of view is that this is really a SCOPEWRITER, not a reproduction – I used instructions and PCB layout from the original magazine article to create it, just like a hobbyist would have done back in the 1970s.

    New Run of Datanetics Rev B are in Stock and Ready to Ship

    Friday, November 9th, 2012

    Price is $75 for each PCB and includes shipping. No components or hardware is included.

    See my web page for details:

    Civil War Picture Analysis

    Friday, November 9th, 2012

    I just added a webpage to my railroad/City Point pages that describes my investigation into this vintage image of City Point.

    City Point image

    City Point image

    Here is the link:

    I have 1 original glossy Mimeo Version 1.0 PCB available

    Sunday, November 4th, 2012

    This would look awesome mounted and framed. Price is $150, same as always. I have a ample supply of new matte 1.01 Mimeo’s also.

    Mimeo 1.01 images now on Mimeo Webpages

    Sunday, November 4th, 2012

    I have now updated a couple of images on my Mimeo Web pages with images of the Mimeo 1.01 that I built using a number of rare vintage components that I managed to obtain over the last few years. Note the gold plated 5 volt regulator, yellow 100 ohm pot and original style TI sockets and the Cinch edge connector.

    Some of these components are very, very hard to find, and often expensive, when you do find them, so don’t expect to find these components in Unicorn’s standard parts kit.