Design and build a wireless timer for students giving talks. The student tlaking would have an LCD display that counts down the time left in the talk. A green LED could come on at some time as a warning, followed by a red one (and a buzzer?) closer to the end.
The person moderating the talk would have access to the timer through a web page.
The project is not incredibly difficult, but there is a wide variety of tasks (hardware/software/networks…) and the system must be robust and low power.