Stamp Stretcher

Archiver

Have a look at http://www.al-williams.com/awce/pak3.htm. For specific
cases you might be able to get by with inexpensive shift registers, etc.


Al Williams
AWC
* Floating point A/D
http://www.al-williams.com/awce/pak9.htm



>

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Original Message

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> From: DUNCANLA [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=697oPAEOt29OIJX8Mb9rBLKms9AMvcsZ_FYMbSxZenMsMi2qGSmxFROFOSF0AKWXHY0DBJwBynNkXEIDwnpb]Duncanla@c...[/url
> Sent: Thursday, June 13, 2002 5:40 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Stamp Stretcher
>
>
> I am almost out of I/O on my stamp (i only have 2 left) and
> possibly want to add a key pad and maybe some other sensors
> to my robot. I am wondering if the Stamp Stretcher is worth
> the $40? Or should i get another stamp and link those
> together? Remember I'm only 15 years old and i'm on a very
> tight budget.
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
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Archiver

I am almost out of I/O on my stamp (i only have 2 left) and possibly want to add
a key pad and maybe some other sensors to my robot. I am wondering if the Stamp
Stretcher is worth the $40? Or should i get another stamp and link those
together? Remember I'm only 15 years old and i'm on a very tight budget.


[noparse][[/noparse]Non-text portions of this message have been removed]

Archiver

>From: "DUNCANLA" <Duncanla@c...>
>Reply-To: basicstamps@yahoogroups.com
>To: <basicstamps@yahoogroups.com>
>Subject: [noparse][[/noparse]basicstamps] Stamp Stretcher
>Date: Thu, 13 Jun 2002 15:40:13 -0700
>
>I am almost out of I/O on my stamp (i only have 2 left) and possibly want
>to add a key pad and maybe some other sensors to my robot. I am wondering
>if the Stamp Stretcher is worth the $40? Or should i get another stamp and
>link those together? Remember I'm only 15 years old and i'm on a very tight
>budget.


I had the same problem and my solution was relatively simple and cheap - AND
gates. An AND gate has 2 inputs and 1 output. The output goes high only if
both input go high at the same time. So what I did was get four AND gates,
which come in a single chip, and I connected one input from each AND gate
all together. So if I put a high onto that single line, one input from every
AND gate would go high at the same time. Then I attached the each of the
remaining inputs from the AND gates, to its own individual stamp pin.

So the output of a specific AND gate would only go high if it's individually
connected input was high *and* if the collective input went high. So it was
possible to use the collective input line as a type of channel selector. By
using a number of these AND gate setups I could select between them by
setting the collective line input to high.

The maximum outputs/input I could get just using AND gates was 8 channels X
8 outputs/inputs which means you can get 64 outputs/inputs from 16 pins. And
unlike shift registers the input/outputs can be treated just like normal
stamp pins because they act in just the same way(except for maybe some of
the special interrupt commands).

I chose this design mainly for operating speed(only a 1 high and 1 low to
change between channels) and also simplicity. There may be more elegant
solutions.

Paul Lugger



















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