I'm working on a temperature controller project using AVR ATmega16 microcontroller.For displaying process value I've used quad 7-segment multiplexed display.In normal mode the display should show the temperature(process value). I want to design an algorithm such that, when I press a key and hold it for few seconds(say 5 seconds) then until it is pressed controller should display process value. Then after 5 seconds it should enter a menu driven program where all parameters associated with the controller can be changed. One such parameter is type of input(say J/K/Pt-100). How to create this programmable delay to enter the menu? Please suggest me a suitable algorithm/source code for the same.