We will construct a really simple circuit based on the arduino documentation (ButtonChangeState).
This example count how many times a button has been pressed.
Here is the virtual schematic
Below you can see the circuit schematic and it's equivalent circuit
From the equivalent schematic we can see that when the pushbutton is not pressed there is no connection between the two legs of the pushbutton, so the pin12 is connected to ground (through the pull-down resistor) and we read a LOW (Vout=0V).
When the pushbutton is pressed, it makes a connection between its two legs, connecting the pin12 to voltage, so that we read a HIGH (Vout = 5V).
The fritzing and Dia schematics can be downloaded from here : CountButton
The photo of our breadboard is posted below.
Now we are ready to implement our demo memory tests.