No he wants to programmatically control the size of current produced by a constant current generator.
Nothing to do with switching resistors.
Have you heard of Ohm's Law ? (E= I x R)=> I = E/R ?
28000 ohms = 28k ohms = 1mA
14000 ohms = 14 k ohms = 2mA
[Regulated Supply]
Resistors all connected at the supply end
Output Term------> < ----[load]+
GND---------------> <-----[load] -
[Transistors or Analog switches to switch any specific resistor in] (COPLETES PATH TO GND FOR ANY RESISTOR)
GND
Turning on R1 ===> EXACTLY 1 mA
This may be more work than the OP wants to do but it is certainly a programmable power supply , whether you like the approach or not. That being said, the circuit you linked looked a good way to go with this, and certainly less work.
@OP,
Here is something to measure the current with for your stepper motor scheme
https://www.sparkfun.com/products/12040
We really have one hand tied behind our back without a DAC. Why don't you get one ?