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2018-10-19, 23:44:17
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Author Topic: 1977 Intel 8255 - fun proximity circuit  (Read 3884 times)
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Thought some of you guys might enjoy the geek factor of this one...a circuit based on a vintage chip used in the original IBM PC.
https://en.wikipedia.org/wiki/Intel_8255

On clearing out some boxes the other day, this circuit was found and tested, it still worked so here it is.
Back in 2007, I bought a load of old gambling/fruit machine boards on Ebay. On which were several socketed chips including Intel 8255's.
After looking at the datasheet ( http://download.intel.com/design/archives/periphrl/docs/23125604.pdf ), several connections were tried out.
The RD pin, Pin 5, was noted to change an LED's output when a coil of wire was connected like an aerial.
After that, other pins were found to change behaviour in various ways.
A lot of fun was had mixing things around and seeing what would happen.
The resulting circuit below is of one version, another very similar version is shown in the video.

The end result is a circuit based on a 37 year old chip, that senses static electricity.
When testing up in Minnesota where we used to live, my wife's daughter came back from school one day and walked past in the livingroom some 8ft away, the circuit LED's flashed with each step :)
Reset is by touching the coil and each LED responds to static 'pressures' in the environment. The internal circuitry forms a mini scale of sensitivity for the 3 connected LED's.

Just a fun 'thing' of a circuit, which may have uses within electrostatic experiments as a sniffer.

There is a mistake in the vid. I should have said the coil comes from a 5 1/4" floppy drive.
[youtube]X7kS_CSyhjI[/youtube]





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To us older digital guys, this is pure torture  ;D
   

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The ability (actually a problem) of CMOS to react to (and usually die from) moving static charges was not something we really wanted.

Just imagine a control card for a massive machine acting like a proximity switch  :D

Believe me. It happened  >:(

Don't be surprised when that 82C55 just quits working  ;)

I deal with Intel bus controllers almost daily. You wouldn't believe how many times I have to insert a passive delay when replacing circuit cards with in-house design replacements.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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Ah, the chip is actually a P8255A so it's quite safe, being non CMOS.
Or, I should say, it was run quite heavily a few years ago and now has behaved itself these years later.
The datasheet was more about wiring connections and functionality of the chip in regular use, so was a bit of an oops. Good descriptive sheet though.
 
Hey, Peter, i'm an old analog guy so digital torture don't phase me, or polyphase me for that matter  >:-)


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Hey, Peter, i'm an old analog guy so digital torture don't phase me, or polyphase me for that matter  Evil


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LOL  ;D
   
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