Replaceable key structure

A replaceable key structure, comprising:

• a key holder having a mounting slot formed thereon, the mounting slot is configured to receive a third key module selectively;
• a circuit board disposed under the key holder;
• a magnetic sensor mounted on the circuit board and positionally corresponding to the mounting slot;
• and
• a contact connector mounted on the circuit board and positionally corresponding to the mounting slot;
• wherein the third key module has a shaft and a spring, the shaft is movable from a topmost position to a bottommost position when an external force is applied, and the shaft is capable of returning to the topmost position by a recovering force of the spring when the external force is removed;
• wherein the third key module has a key housing, sides of the key housing are respectively formed with a plurality of engaging members for fixedly engaging the third key module in the mounting slot;
• wherein the third key module further includes a magnetic element, the magnetic element is connected to a bottom end of the shaft, and the magnetic sensor is positionally corresponding to the magnetic element;
• when the magnetic element approaches the magnetic sensor following a displacement of the shaft of the third key module, the magnetic sensor outputs an analog signal by inducing a magnetic field of the magnetic element, and a strength of the analog signal is changed following a distance between the magnetic element and the magnetic sensor;
• wherein the third key module includes a trigger switch, the trigger switch is turned on to generate a digital signal when the shaft of the third key module is pushed downward to a triggering position by an external force, wherein the trigger switch has at least one contacting portion disposed on a bottom of the third key module, and the at least one contacting portion is positionally corresponded to the contact connector;
• when the third key module is disposed in the mounting slot, the contacting portion is capable of contacting the contact connector for transmitting the digital signal to the circuit board.