I've designed a h-bridge driver with atmega48 and irlz24n mosfets. LM393 comparator will be used to check inductance of coil. When voltage on coil drops to 0V after turning off voltage on upper bridge stage, MCU will check time and will be able to tell how fast it dropped. This will hopefully have enough resolution to get position in range 1-100. With 50mm length that means 0.5mm physical resolution. After weekend I will be testing this with oscilloscope.