1 am postings ... You'd think I would learn, but where's the fun in that?

OK, based on Ian's snotty little reality check, try this.

Thanks for that remark!
It did make me wonder if there might be a ladder circuit that would work with a voltage and open-circuit As the two states.

 

t did make me wonder if there might be a ladder circuit that would work with a voltage and open-circuit As the two states.

I tried various approaches for that with an R-2R network, but was not successful.
Doesn't mean there isn't one though.

 

For a slightly increased cost, the circuit assembly becomes pretty simple. Two 4-bit R-2R resistor networks and one 1 x 8 pull-down resistor network.

ak

 

I tried various approaches for that with an R-2R network, but was not successful.
Doesn't mean there isn't one though.

It doesn't have to be linear, as long as it is monotonic.

 

For a slightly increased cost, the circuit assembly becomes pretty simple. Two 4-bit R-2R resistor networks and one 1 x 8 pull-down resistor network.

Would that be cheaper than four 1% resistors?

 

It doesn't have to be linear, as long as it is monotonic.

Okay.
Here's the sim with an R-2R network.
The minimum step is about 35mV.

 

Would that be cheaper than four 1% resistors?

You're right. When you drop down to a 4-bit section, resistor tolerance is much less of an issue.

I would think that the circuit in #20 would be good enough. Hard to beat just 10 resistors.

ak

 

Going back to the circuit in post #21.
If you use a 9-way isolated (18-pin) resistor network, you can achieve the values as:
2 in series
1
2 in parallel
4 in parallel

or

2 in parallel
1
2 in series
4 in series

Whilst network resistors have only average tolerance, the matching between individual resistors in the array tends to be rather better.