On April 11, 2005 04:06 pm, 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.

The resistor network is a good idea, but you wouldn't want to use 8 
buttons on an 8bit analog input. Step back to 7 or 6 buttons unless you 
use a higher res analog input.
>From a manufacturing point of view, I don't like having both power lines 
on the same leg of a switch, but yes, the SPDT 0v/5v idea works if you 
can use SPDT. 

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