You are right but If you look at it in detail then you also need ceramic
Cap for filtration I just gave him general idea.

Andre Abelian


-----Original Message-----


> +VDD 5v
>    |
>    R1
>    |            /
>    *----------o/  o----------|
>    |                         |
>    |                         |
>    |                         |
>    R2                        |
>    |                         |
>    |                         |
>    |            /            |
>    *----------o/  o----------*----------o to pic ADC input
>    |                         |
>    |                         |
>    |                         |
>    R3                        |
>    |                         |
>    |                         |
>    |            /            |
>    *----------o/  o----------|
>    |
>    |
>    |
>    R4
>    |
>    |
>    |
>   GND

That would work except that the PIC pin needs to float to a well defined
"no button pressed" level when no button is pressed.  This will draw a
significant current in the divider chain, because the pullup or pulldown
can't be more than 10Kohms, and the divider would have to be
significantly
less to overcome it and still produce reasonable size step changes.  You
also have to think carefully about what happens when more than one
button
is pressed at a time.  You could work out a scheme where every
combination
produces a different voltage, but then we'd be back to high parts
tolerance senstivity for more than a few buttons.

By the way, you could lose either R1 or R4 in the diagram above, but not
both.


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(978) 742-9014, http://www.embedinc.com

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