Contact Bounce - Simple Debounce RC Circuit Question
It's too late for me to think about sketchy circuits found on the internet, but the more conventional RC debounce is this:







simulate this circuit &ndash; Schematic created using CircuitLab

It's operation is simple. A t=0-, with the swtich open, C1 charges up through R1 and R2. This takes \$5(R_1+R_2)C_1\$ seconds without the diode and \$5(R_1)C_1\$ seconds with. After a sufficiently long time, we can say \$V_c = +V\$. When the switch closes, C1 discharges through R2 in \$5R_2C_1\$ seconds. Once the switch opens again, C1 will charge back up in either \$5(R_1+R_2)C_1\$ or \$5(R_1)C_1\$ seconds depending on if the diode is included. 

This scheme gives a logic low with the switch close, but can be reconfigured to give a logic high by switching a couple components around. I'll leave that as a thought exercise for the reader.