A handheld computer assembly for integrating an input device with a handheld computing device is disclosed. The mobile unit sets a flutter-preventing threshold relative to an event 1C at a first value when the communication level of a monitor set cell does not fall within an emergency range, and at a second value lower than the first value when the communication level of the monitor set cell falls within the emergency range. An input terminal of the buffer is connected to control terminals of the transistors of the first stage through a first open loop driving circuit. A specified number of balls are fit into the running channels.