Switch network

Claim 1

A network for ascertaining the state of a plurality of sensing devices, which comprises: a communications line; a master controller connected to the communications line for generating address signals thereon, the master controller including, (a) address generator means for establishing a sequence of station numbers, (b) oscillator means for generating sinusoidal waveforms, (c) analog switch means for coupling the oscillator means to the communications line, the analog switch means being operated by the address generator means to sequentially generate series of sinusoidal waveforms on the communications line, the number of such waveforms in each series being determined by the station number established by the address generator means, and (d) a receiver circuit coupled to the communications line and being operable to read the voltage level of the communications line a predetermined time interval after each series of sinusoidal waveforms is generated; and a remote station connected to the communications line and connected to an associated sensing device, the remote station including: (e) counter means for counting the number of sinusoidal waveforms in each series, (f) comparator means coupled to the counter means and being operable to generate an enabling signal when the counted number of sinusoidal waveforms corresponds to a preset station number, and (g) response means coupled to the comparator means and the station's associated sensing device for generating a preselected voltage level on the communications line during the predetermined time interval after the series of sinusoidal waveforms is generated when the enabling signal is present, the voltage level being indicative of the state of the station's associated sensing device.