Keybounce

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Keybounce is the mechanical phenomenon resulting from switch contacts bouncing off of one another, resulting in several changes in state in a brief period.

In a circuit, an electrical current flow is permitted when a switch is closed. Switches are designed to prevent the flow of current when the switch is open. Buttons and keys such as those on a keyboard are generally simple contact switches.

However, in practice, vibration and other mechanical faults usually prevent complete contact from being made initially. The switch will bounce open and closed for a period of time while the contact settles. In computer systems reading switches as an input device, this causes the system to register several presses of the key or button while the contact settles.

One method of dealing with this problem introduces a delay between successive checks of switch states. By scanning less frequently, keybounces are less likely to be registered as duplicate keystrokes. A better method is to low pass filter the input, for instance by requiring several consecutive measurements to agree before registering a change.