>
>this could be done with one i/o line and about $3.75 USD in components
> OR three i/o lines and about $1.00 USD in components
> OR seven i/o lines and about .10 USD in components
> OR twelve i/o lines and no additional components


Thanks for all the suggestions:

I've seen the three pin A-D solution, with resistor networks, but it used
1% tolerance resistors in various odd values - as someone's pointed out
recently this is unhelpful froma manufacturing point of view.

I hadn't thought of the shift register idea though. I suppose that actually
a '554 or '61 (with 13 i/o pins) could read twelve pins and clock the data
out of the thirteenth in some kind of slow async. serial protocol - and it
can sit and do this 100% of the time. So only 1 pin is needed on the
primary PIC. And it might as well do the BCD-binary conversion while it
sits there.

And while I sit here writing this, it's just occured to me that there's a
remote-control IC (HS12E I think) that takes 12 binary inputs and clocks
them out in an odd but decipherable PWM format. That might be the cheapest
single pin solution.