Magnetoresistive switch mechanism for telephone matrix key pads - has magnetically governed keys which alter conductivity of two adjacent conducting tracks at cross-point

摘要

The keyboard button consists of a vertically-moving shaft (303) at the lower end of which is fixed a permanent magnet (311). An insulating bush (307) is inserted in the entry hole through the keyboard plate (201) which is made from a magnetic mateiral. When material. When the button is depressed a magnetic attractive restoring force returns it to its rest position. The magnetic plate also provides an electrical shield for the keys. A network of conducting magneto-resistive tracks (319) is deposited on the insulating substrate under the keys. The network is in the form of a series of parallel straight rows overlaid with a series of serpentine tracks which appro ch the straight rows to form short sections in which the two tracks are parallel, which thus create the 'cross-points'. When the magnet is adjacent to the substrate, the field of the magnet, which is concentrated due to its chamfer-grooved outline acts on the two parallel tracks simultaneously to locally increase their resistance. Insulated stand-off pillars (315,314) maintain the magnetic keyboard plate and the substrate correctly spaced apart.