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Old 01-08-2006, 02:11 PM
Grant Stockly Grant Stockly is offline
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Join Date: Jan 2005
Posts: 447
Default The RamWall...

It all started back in September 2005. I was talking with my buddy Henry (who I've never met in person) and talking about how big and "cool" the older computers were. Massive banks of PCBs just for sub-megabytes of ram. I talked about wanting to build 4MB of ram for a Macintosh Plus out of a few thousand RAM chips. Thats when the first "you're crazy" came out. When I hear that, its a challenge.

Fanout issues aside, the cost would have been huge. It was left at that for 3 months. Just a fantasy.

On December 31st I was checking up on www.applefritter.com to see what was going on. I found out that someone else had created an Apple 1 kit, just what I was planning on continuing! (I had started the project about 9 months ago). So I tried to think of projects for it. Ethernet card, MP3 player...RAM visualization? A led for every bit in the computer? Here we go!

About 4 years ago I was on ebay, just looking (like womeon window shop
). I came accross 50,000 green LEDs for $300. I had to have this!

4kbyte (32768 LEDs) would be a LITTLE to big. with 400mil spacing, 72x80" in size...and a lot of cash in PCBs. I finally settled on 1kbyte as a goal, and it grew to around 1.7k by the end of the project. The idea in the beginning was to organize the display into 8x8 blocks with spacing for labels. This wastes both wall space and other uses for the display. At the end, it turned into a 180x99 bitmap display.

What am I going to do with this display? Display the physical memory locations in an Altair. The Altair is all about blinking lights, but you can only see one byte at a time! Not enough! I think it would also be fun to play pong on the Altair.

The final display will have an interface with dual port SRAM on the Altair. The display will be mapped directly to the memory, so a program to play pong will just be modifying areas in memory. This is similar to a lot of older computers like the Apple II and Macintosh.

In the next posts I will copy what was discussed on sci.electronics.basics, and after that post pictures of the actual PCBs under construction.
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