pin reducing tri-state logic Charlieplexing etc

tonyp12

There are 3-to-8 decoder ic,
but I have not seen any decoder ic that take advantage of the tri-state.


As the the prop pins can have its pins in 3 different states.
output: on
output: off
input : high-impedence (disconnected)

3pin to·6 LED·or 4pin to 12 LED Charlieplexing is pretty easy.



1pin to 3pin decoder?

2pin to 8pin decoder logic?




Post Edited (tonyp12) : 2/5/2010 6:00:38 PM GMT

Ale

I tried doing Charlieplexing for a keyboard... without diodes... it does not work :-( where is the bin of failed implementations again ?

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Rayman

Clemens did a cool Charlieplexing LED matrix demo... I think it was 10x10.

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tonyp12

There· is a trick solution to only using 4 diodes, multi key presses not recommended.




http://electronicdesign.com/content.aspx?topic=novel-switch-interface-scheme-reduces-microprocess&catpath=analog-and-mixed-signal
·

Rayman

very interesting!

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Mike Huselton

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JMH

tonyp12

Side effect with ripple counter is that you would have·go from·0 to the number you want, one number at a time.
it could be up to 4096 clock cycles before you have the output you want.

It's Ok with displaying LED as the slight flicker should not be notisable to the human eye.

And also it does not implement the tri-state feature i'm looking for.


·

tonyp12

Cluso99·uses this in his new Latchblade.
It uses 4 resistors and half of a http://www.nxp.com/documents/data_sheet/74LVC86A.pdf
PhilPi created something similar for the 1 pin-vga-sync using inverting buffers instead of XOR gates.


When the prop is tristate, both XORs output a "1".
When the prop drives the pin "0", the lower XOR outputs "1" and the upper XOR outputs "0".
When the prop drives the pin "1". the lower outputs "0" and the upper outputs "1".


Post Edited (tonyp12) : 2/7/2010 2:20:05 AM GMT

Mike Huselton

LatchBlade?

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JMH

tonyp12

link to MemoryBlade and LatchBlade
http://forums.parallax.com/showthread.php?p=878838
·

VIRAND

With Resistors, you can put around a hundred keys on two wires.
For LEDs use shift registers. I have a RG dot matrix sign that works that way I think, but with so many it also has latches.

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