Russell McMahon wrote:
>> Could be made into a page on PIClist, then it'll be available
>> until the Internet breaks
>>     
>
> It's broken.
> It was broken years ago.
> As soon as the first sites were opened to the public everything 
> started to go wrong.
> Its obviously far too dangerous to go out in public, let alone fly.
> I think we should just give them ...
> Oh.
> Wrong thread.
> OK ..
>
>
>         R :-) M
>
>
> PS: Reading multiple switches on one pin is not uncommon but is a very 
> useful idea. Having pre-rolled code for those who are unaccustomed to 
> this is a good idea. Even more than 7 switches should be possible 
> using the same general method, subject to the accuracy of the ADC and 
> the resistor tolerances. Too many and you start to get annoying 
> resistor values unless you start to get innovative in the way you use 
> them. I don't know how Bob's method works in detail but if you wanted, 
> say, 16 switches you could try say 4 divider chains with similar 
> valued resistors in the switched portions and a different value above 
> this combination to the pin plus another resistor from pin to supply. 
> That way you get a series parallel arrangement.  ...
>
>   
Russell, if the switches are crosspoint type (0.0 on resistance) you 
could have 150 switches on a
single pin, but most switches these days are carbon button, which vary 
from 1 to 200 ohms when
closed. That amount of error makes those switches unreliable. Also, the 
normal resistor error also
makes a difference. If all of your resistors are 1%, about 20 switches 
are possible with perfect
reliability.

--Bob

 

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