Turn on bounce keys
Turn on bounce keys to ignore key presses that are rapidly repeated. For example, if you have hand tremors which cause you to press a key multiple times when you only want to press it once, you should turn on bounce keys.
Click the icon at the very right of the menu bar and select System Settings.
Open Universal Access and select the Typing tab.
Switch Bounce Keys on.
Use the Acceptance delay slider to change how long bounce keys waits before it registers another key press after you pressed the key for the first time. Select Beep when a key is rejected if you want the computer to make a sound each time it ignores a key press because it happened too soon after the previous key press.