The digital Potentiometers made by analog devices (AD5204) has 255 positions can be adjusted by the microcomputer that can receive commands from the computer. This is a great way for analog circuitry to have digital control. This is a chip with 4 digitally controlled POTs and the pots can be daisy chained to have multiple chips controled by a single SPI interface.
Digikey Part Number: AD5204BN10-ND
AD5204 - 4-Channel, 256-Position Digital Potentiometer