Switch Inputs

The diagram below shows an example of a control panel switch connected to the game board. R1 is a "pull-up" resistor holding the input of the IC buffer at 5V level (high) when the switch is opened. Closed switch connects ground to the input changing the input level to 0V (low). The capacitor C1 acts as a filter against noise, resistor R2 provides protection for the input of the IC.