Depends on which peripherals you have. * A good start is a stop watch (if you have a 7seg and buttons available) * Implement a digital function generator with

Depends on which peripherals you have. * A good start is a stop watch (if you have a 7seg and buttons available) * Implement a digital function generator without using look-up tables. (Can read values over serial) * If you have access to an ADC and DAC implement an echo filter, then a tuneable butterworth