You are allowed to chose your own topic, however, it should meet the minimum requirements listed below. 
Your setup should feature microcontroller to microcontroller communication. Additionally you must use at least 3 of the following systems:

Matrix based input
Matrix based output
Timers
Interrupts
EEPROM

You should create your circuit, program your microcontrollers, design physical look and layout of your components on the final product. Your document should contain an introduction explaining the product, bill of materials including prices, screen shots of the circuit, physical layout shortly explaining how the product can be used. Additionally, you should also design metrics that will measure the usefulness of your device and rank your device according to these metrics. These could be user interface design, safety, environmental aspects, etc… You should write one page on this topic in your document. Finally your document should contain a conclusion and your codes.