The current issue of Circuit Cellar has a feature article authored by regular Forum contributor Dick Cappels. Good job, Dick.
"Microcontroller-Based Digital Lock-In Milliohmmeter
FEATURE ARTICLE by Dick Cappels
A milliohmmeter is a handy tool for tasks like measuring a switch’s contact resistance and checking the trace resistance on a PCB. Dick built his own microcontroller-based digital milliohmmeter using lock-in amplifier topology. The project is simple as long as you follow Dick’s
instructions. Get ready to improve analog performance with a microcontroller."