The RamWall...

[Grant Stockly]

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.

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
Newsgroups: sci.electronics.basics
Subject: Wall of RAM
Date: 1 Jan 2006 19:25:50 -0800
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A while back on ebay I was just looking around and came upon 50,000
LEDs.

Ebay is a dangerous place, I can understand how women go to the store
and spend $800 window shoping.

$300 later and I have 50,000 LEDs in the mail

Anyway, I gave away around 1,500 to friends. I still have MANY of them
left.

I thought a "fun" project would be to create a "Wall of RAM". Now it
would be fairly easy to emulate the ram and display the results on the
wall using a CPLD, but what about actually making real ram?

Does anyone think its possible to use capacitors and high current
drivers to use the LED+capacitor combination as ram?

The goal of the project would be a wall of cards, say 4k of ram max.
This wall of ram would interface to either the Altair that I bought OR
the Apple 1 kit that I bought on ebay.

What do you guys think? It seems that with some RAS/CAS decoding logic
that it shouldn't be too hard. The cons of this project are the cost
of 4,096 capacitors and PCBs. The pros of the project are, well, it
would look really neat.

Tell me what you think.

Grant

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
Newsgroups: sci.electronics.basics
Subject: Re: Wall of RAM
Date: 1 Jan 2006 19:42:51 -0800
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Well, in the excitement I forgot that 4,096 bytes is 32,768 bits. A
little out of my range.

So maybe we settle on 1k of ram. I don't think I have 32,000 leds of
wall space to spare!!!

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
Newsgroups: sci.electronics.basics
Subject: Re: Wall of RAM
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On second thought, a 1k ram wall would be 121x121" square. I just got
done drafting it. I think maybe I should consider one 256 byte array
and see how it goes.

What considerations will I have to make for wire length? Possibly use
a differential transciever set?

[Grant Stockly]

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From: Jasen Betts <j...@free.net.nospam.nz>
Subject: Re: Wall of RAM
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On 2006-01-02, logjam <g...@cmosxray.com> wrote:

> On second thought, a 1k ram wall would be 121x121" square. I just got
> done drafting it. I think maybe I should consider one 256 byte array
> and see how it goes.

when you said 4K I thought you meant bits. and that it sounded possible
but lots of work.

> What considerations will I have to make for wire length? Possibly use
> a differential transciever set?

reduce the clock speed until it starts working?

Bye.
Jasen

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
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Subject: Re: Wall of RAM
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All right, I'm not crazy any more. If I even try this I'll just use
some dual port sram and fake it. That should be easier and allow a
switch to choose which 1k bank of the memory to look at. A little more
flexible.

[Grant Stockly]

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From: "Bart" <bborb@fusedotnet>
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Subject: Re: Wall of RAM
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"logjam" <g...@cmosxray.com> wrote in message
news:1136203193.354765.163350@o13g2000cwo.googlegr oups.com...
> All right, I'm not crazy any more. If I even try this I'll just use
> some dual port sram and fake it. That should be easier and allow a
> switch to choose which 1k bank of the memory to look at. A little more
> flexible.
>

How many lights/led's would that be? Calculating your original thoughts
showed scary amperage and blinding candle-power. I could be wrong, just a
thought.
Bart

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
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Subject: Re: Wall of RAM
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I don't know. These aren't very bright LEDs.

Here is what 1kbyte would look like:
http://media.diywelder.com/images4/060102-1kvisual.jpg

and a 1 to 1 scale:
http://media.diywelder.com/images4/0...visual1to1.jpg

You may think its crazy...but what am I supposed to do with my 50,000
LEDs???

[Grant Stockly]

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logjam wrote:
> I don't know. These aren't very bright LEDs.
>
> Here is what 1kbyte would look like:
> http://media.diywelder.com/images4/060102-1kvisual.jpg
>
> and a 1 to 1 scale:
> http://media.diywelder.com/images4/0...visual1to1.jpg
>
> You may think its crazy...but what am I supposed to do with my 50,000
> LEDs???
>
Put all of them in an array (~220 * 220) ,wire them in
groups serial an parallel, and in desert sun you have a nice
solar panel.(I do not know what the output would be) -)-)-)

[Grant Stockly]

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From: "logjam" <g...@cmosxray.com>
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Subject: Re: Wall of RAM
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Up here in Alaska we don't have much desert sun, so that might be a
problem.

Here is a picture of a 26x22 array. I got this far and then was worn
out. Used a little over 500 LEDs on this one! I was worn out because
the board was wired completely by hand. I would use a PCB from a
company on this project...

http://media.diywelder.com/images4/0...dback_1020.jpg

http://media.diywelder.com/images4/0...front_1021.jpg