You are grounding each pin adc input will get the same voltage
On every switches In your schematic you are changing the current not the
voltage.
To change the voltage use some thing like this
Use 1% metal film resisters R1 thru Rx can be any value
In your case you can use 8x1k resisters.


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



Andre Abelian




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

> Olin - I'm not entirely sure I agree with multiple keypresses showing
> as the highest priority keypress.  Maybe I missed the original post,
> but I didn't read where he described the actual wiring.  IF he's using
> the resistor ladder as nothing more than a multi-tap voltage divider
> and the switches do nothing more than route a particular tap to the
A/D
> input, then multiple keypresses will short out part of the ladder,
> giving you an A/D input not representative of either valid keypress.
>
> Do you disagree?

I was envisioning a different topology from the one you describe because
it is too sensitive to part tolerance.  The original poster was vague
about his topology, so I went with the most sensible approach:


  +V
   |
   R
   |
   *----------*-------  to PIC A/D pin
   |          |
   |          o /
   |           /
   R          o
   |          |
   |         GND
   |
   *-----------
   |          |
   |          o /
   |           /
   R          o
   |          |
   |         GND
   |
   *-----------
   |          |
   |          o /
   |           /
   R          o
   |          |
   |         GND
   |

  etc...

Note that the various Rs might not be the same value.  The top R should
be
larger than the others, which could be the same for simplicity.


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