I need some practical hints. Actually, how bad is automotive environment?
For example, may I use direct connection of buttons/contact switches to the inputs of AVR chip, with internal pull-up resistors?
Or I need to use external, pull-up resistors with lower resistance?
Or I need optocouplers on inputs?
Is it possible to use software instead of hardware? (Some sort of filtering)
Let say, the wires from the CPU to the buttons/sensors are 1..2m long.