Abstract: A plurality of magnetic reed switches are arranged in a plurality of rows and columns. Mounted above the plane of the reed switches but in close proximity thereto is an electromagnet. Stepping motors are capable of moving the electromagnet so as to overly any one of the reed switches. When the electromagnet is in position over a selected switch, it can be energized to selectively turn the switch on or off. A sensing circuit including a Hall effect transistor travels with the electromagnet and senses if the reed switch below the sensor is on or off.