I just wanted to add that this is being used heavily in many expensive 
surveillance cameras
Uses a single input pin to handle a host of switch inputs. They publish 
the R values to be
used at each switch. Since the unswitched value is 5V, and there are 
about 8 switches, it
works out that each diffferent level is only about 0.7V.

I used a CD4051 and 1% Rs to control the camera with me PIC. Very nice.

--Bob

Harold Hallikainen wrote:

>>Yup, you can read multiple keys, but you can't quite do it in the manner
>>Mike is suggesting. Mike is close, but has to change his resistor
>>ladder to R, 2R, 4R.... to catch multiple keypresses and I wouldn't
>>recommend going more than 5 buttons on a plain PIC pin (using the
>>method kRC = T), or 7 buttons on an analog input since by the 7th
>>button you're at 64R (getting close to 1% tolerance values) .
>>    
>>
>
>
>How about just going R, 2R like an R-2R D/A? It's simplest if your
>switches are SPDT and switching between +5 and ground. You could use
>resistor networks where the matching between resistors is much better than
>the absolute tolernance.
>
>Harold
>
>
>  
>


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