http://www.robotreviews.com/chat/viewto ... Dock+based
It might be easier to use an Arduino or PIC microcontroller and LCD display kit but I had parts to make this hardware solution.
The clock has a 1.5v battery and applies the battery voltage to the key pad when pressing buttons. The previous method of using a switching transistor for the button press proved unreliable, with the voltage drop across the transistor, so a reed relay is used in the circuit below. As I could not get the transistor to close the relay with the weak pulse from capacitative coupling on departure and arrival, 555 one shot drivers are used. As the weak trigger pulses cannot be combined through diodes with their voltage drop, dual one shots are used with the outputs combined through diodes instead.
This circuit taps a vacuum-docked indicator led on the Samsung dock to detect arrival and departure; additions can be made for various sensing methods. One comparator is configured as a latch so the clock runs only on the first, longest run in a series of recharges, with an led to indicate when the clock is ready to time. On return to base the led goes out and the time remains on the clock through subsequent runs until the reset button is pressed.
For more analysis of multiple charge runs the WiFi cell phone apps on the newer vacuums can be used. Samsung's SmartThings app replacing their older SmartHome requires a large phone with 3gb memory when other apps are used, though specifies 2gb needs, and my phone is too small at the moment.
Of course this hardware timer could be used with older vacuums lacking WiFi features.