Buttons with modulated bias voltages

摘要

Electronic devices may use buttons to gather user input. Button status monitoring circuits may be provided that apply a time-varying bias voltage to each button. The time-varying bias voltage may be held at a fixed non-zero level when the state of the button is being monitored and may be held at a level of zero volts when the state of the button is immaterial and is not being monitored. The reduction of the bias voltage across the button when the button is not being monitored prevents undesired acceleration in dendritic growth when the electronic device is exposed to moisture. The bias voltage may be pulsed by using a control circuit. The control circuit may generate a series of square wave pulses that are applied across the terminals.