Hardware and Timer Interrupts - Exploring Arduino: Tools and Techniques for Engineering Wizardry - page 264

Figure 12-3: Creating a debounce circuit: adding a capacitor and a resistor
Adding the resistor in series with the switch (R2 in Figure 12-3) is not com-
pletely necessary; without it, the capacitor would discharge (almost) instantly
and would still be recharged quickly enough by R1. However, this rapid dis-
charge over the switch could damage cheap buttons. Including the 100Ω resis-
tor decreases the discharge time and keeps all your components safe. This,
however, adds a discharge curve to your output. You can see this effect in the
oscilloscope in Figure 12-4.
Figure 12-4: Signal bouncing removed with a RC circuit