On/Off Switch

• Problem: Pushing a button toggles a LED between on and off.
• Without any logic, the LED is lit when the button is pushed and goes off when the button is released.
• Now, the first push of the button switches the LED on, the second push switches it off, etc.
• Considerations: A memory element (flipflop) is required to remember if the LED is currently on or off.
• The current state determines the next state - the next state is the inverse of the current state.
• This suggests that we connect the inverse output Q' of the flipflip to the D input of the flipflop.
• The new state is to be entered when the button is pushed.
• This suggests that the button be connected to the flipflop's Enable input.