William Couture wrote:

> I know that you can use a ADC input and a series of resistors in place of
> jumpers (if you are short on input pins).
> 
> My questions are
>    * how many "jumpers" can you reliable read with a 10-bit ADC?

LOTS. Depends on the precision of your resistors and the contact 
resistance. 8 if you can get 0.1% precision Rs. (256 states)

>    * can you use arbitrary bit patterns?

Yes. You basically build an R-2R DAC out of discrete Rs.
Or use a real DAC with the jumpers being your DAC input word.
Then 10 bits is theoretically possible. 9 pins is probably doable.
8 is no problem.

>    * suggestions for resistor values?

Depends on what your power management needs are. Strobing it a good
way to save power.

You could also try using a shift register to read as many bits as you
like. It's doabale with just 2 pins. You use an RC network off the clock
out to strobe in the current data (74HC595 for example).

There is also a way to do it (shift register reading) with just
ONE pin, but that's one for a 'design ideas' submission.

Robert
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