Describe design of a system built-in the mailbox, which sends information to the owner when a new piece of mail appears inside the mailbox. The information is sent via the cellular network. The device should be able to estimate whether the piece of mail is a leaflet, a letter, a postcard or a package by sensing its weight. The device is battery-powered and thus, most of the time, should be in a low-power mode and activate only when a new piece of mail appears. The system is based on one or more Arduino boards and additional components. Design the structure of the system, select components and sketch the structure of the system software