# Wall of RAM

L

#### logjam

Jan 1, 1970
0
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

L

#### logjam

Jan 1, 1970
0
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!!!

L

#### logjam

Jan 1, 1970
0
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?

J

#### Jasen Betts

Jan 1, 1970
0
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

L

#### logjam

Jan 1, 1970
0
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.

B

#### Bart

Jan 1, 1970
0
logjam said:
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

S

#### Sjouke Burry

Jan 1, 1970
0
logjam said:
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/images4/060102-1kvisual1to1.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) -)-)-)

B

#### Bart

Jan 1, 1970
0
Just a thought, if you're going thru so much labor, maybe have a board
drilled to make a significant sign, shape, or lettering that you could sell
to a business or school, donate to a church.
Bart

T

#### Tim Williams

Jan 1, 1970
0
logjam said:
Anyway, I gave away around 1,500 to friends. I still have MANY of them
left.

Say, do you have a range of colors? I'm probably stupid to ask for it, but
a couple hundred LEDs could be nice for a whacky project. Probably is
stupid since about the only indicator I use regularly is my oscilloscope...
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?

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

Not that I know of. LEDs are exponential, not negative-resistance, like
neon lights are. If you had gotten a couple ten-thousand neon lights, you
could do it (although clock would have to be slowed to the 10kHz range!).
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.

You'll need at least 8,192 transistors and 16,384 resistors, to make yea
many RTL inverter R-S flip-flops. To burn LEDs, I suggest using a red to
indicate OFF and a green to indicate ON for each bit. A negative or
positive pulse to the base (supplied by resistor or capacitor) sets state,
while electrical state is read by collector voltage. RTL with typical
transistors will switch in a 100-200 nanoseconds, so should be able to keep
up with a standard clock. I'm not sure how you're going to address it,
since you need essentially eight 9 to 512 decoders!

Lesse, at 5mA per LED, that's a good 25 amperes supply current. 'Gonna want
that as low as possible, i.e., 5V or so. Total dissipation will be on the
order of 125W, not too bad.

For the wiring, runs several feet long will want to be coax or at least laid
against a ground plane or something. Terminating resistors might be a good
idea.

Tim

R

#### Rich Grise

Jan 1, 1970
0
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
....

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

Yes, but it'd be a nightmare to design; you'd have to come up with
a whole refresh scheme. I'd use flip-flops or real 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?

I think you're crazy, but it does sound like a kewl idea.
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.

If you want to do it, (and have the cash) do it. "If you build it,
they will come". Take pictures, and _then_ see what other people
think.

Good Luck!
Rich

D

#### Daniel Pitts

Jan 1, 1970
0
logjam said:
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/images4/060102-1kvisual1to1.jpg

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

I've been looking for some for a similar type of project.
My idea was to have a computer case that displays certain patterns,
graphics effects such as:
plasma http://www.coloraura.com/artwork/?applet=Plasma
Fire http://www.coloraura.com/artwork/?applet=Fire
Conway's Game of Life (Haven't posted the applet for that one yet)

I might be interested in buying a few thousand LEDs from you
Depending on their specs.

L

#### logjam

Jan 1, 1970
0
This started as a little thought. Now I'm kind of excited about it!

Rather than have gaps all over the place I've designed it to have LEDs
that are always off in binary view mode. Labels could be placed over
the dead LEDs. Then in a normal mode the display could be used as a
giant bitmapped display. This might make the LED wall more attractive
to other people.

I know, I messed up on all the captions. The COST is correct. $255 vs$350

1296 bytes
400 mil spacing, 10368 bits of display, 4212 LEDs wasted in binary view
mode
http://media.diywelder.com/images4/060103-1728bits_400milspacing_full.JPG
http://media.diywelder.com/images4/060103-1728bits_400milspacing_1to1.JPG

1280 bytes
300 mil spacing, 10240 bits of display, 4160 LEDs wasted in binary view
mode
http://media.diywelder.com/images4/060103-1280bits_300milspacing_full.JPG
http://media.diywelder.com/images4/060103-1280bits_300milspacing_1to1.JPG

L

#### logjam

Jan 1, 1970
0
The 400mil display would be a 180x81 pixel display.
The 300mil display would be a 160x90 pixel display.

B

#### Bob Monsen

Jan 1, 1970
0
Up here in Alaska we don't have much desert sun, so that might be a ^^^^^^
problem.

Ah, that explains it. Winter darkness... You crave LIGHT!

--
Regards,
Bob Monsen

"False facts are highly injurious to the progress of science, for they
often endure long; but false views, if supported by some evidence, do
little harm, for every one takes a salutary pleasure in proving their
falseness."
-- Charles Darwin

M

#### Michael A. Terrell

Jan 1, 1970
0
logjam said:
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/images4/060102-ledboardback_1020.jpg

http://media.diywelder.com/images4/060102-ledboardfront_1021.jpg

What part of Alaska? That's a very large area. I was there in '73 &
'74 at Ft Greely.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

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