/diy/ - Do It Yourself

I had this idea of controlling a power transistor with a variable base current. So I experimented by using a ULN2003 transistor array to vary the base current by driving a sufficient number of port pins high. This way the transistor's base could be driven by a sufficient current when its emitter current varies.
I'd like to measure the load current, and feed it into analog-digital converter of a microcontroller and it would then drive a correct number of port pins high. What kind of arrangement should I use for measuring the current?