Announcing New VDM-1 Reproduction

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Announcing New VDM-1 Reproduction

Postby physicsrob » August 26th, 2021, 6:54 pm

Hi All,

It's with great pleasure that I'm announcing a new S-100 board, a VDM-1 reproduction which I've been referring to as the VDM-2021.  Now anyone can build a terminal-style text video card for the S-100 bus.
Details of the board, ordering instructions, and much more can be found here: https://physicsrob.github.io/vdm1/
The short history of this board is that I reached out to Lee Felsenstein to ask him what he thought of me reproducing the VDM-1.  He was reluctant for me to reproduce the original PCB layout since the original layout had problems (like the ribbon cable), so he suggested I create a new layout for the original VDM-1 circuit.  So that's what I did!  Lee provided valuable feedback throughout the process.
Initially I will be selling the bare board for $30, or a partial kit for $90 which will include everything necessary to build a VDM-2021 that is not readily available through Jameco or similar electronics distributors.  Specifically the partial kit will include:- 1 x VDM-2021 PCB
- 1 x Character generator ROM (either MCM6574P or MCM66740)
- 8 x 2102 memory chips (equivalent to the 91L02 or 21L02)
- 1 x DM8131 bus comparator
- 1 x DS8836N bus receiver
- 1 x 93L16 binary counter
- 1 x heat sink
- 1 x BNC PCB connector 

All remaining ICs are 74-series TTL or 4000-series CMOS.
This is my first S-100 board, and I'm doing this as a hobby, so a few disclaimers:1) I haven't put in the order yet for the final production PCBs (I've had prototypes printed and I have assembled them successfully).  I will most likely place the order in about two weeks, after gathering the initial orders, and depending on the response.2) The hardest component to obtain is the character generator ROMs.  I have about 50 ROMs available for these kits, but I have no idea yet if that's sufficient or way overkill.  I believe I have a reliable source for more ROMs if necessary.3) This is a hobby project, and I have a full time job, so shipping may be delayed, and while I will attempt to support builders, I can't make any guarantees of support.4) While this board should be straightforward to assemble, this is not a beginner board.  There are 48 ICs, and I highly recommend having a scope on hand to follow the integrated assembly-test procedure outlined in the original VDM-1 manual.
I hope you all find this valuable and enjoy!  I've had a blast putting this project together, and it's very satisfying to use BASIC on my Altair displaying the output through a vintage monitor directly from this board.  I'm excited to play Trek-80 as well, although I haven't gotten a keyboard working with Trek-80 yet.

Cheers,
Rob
physicsrob
 
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Re: Announcing New VDM-1 Reproduction

Postby wperko » March 10th, 2022, 6:58 pm

Hi,

I am almost done building my VDM-2021, but I need a schematic to make a fix to become a Sol-20 video board. Please email me direct.

wperko brainless org
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