Code generator for feeding data into a telephone channel

Claim 1

A portable data code generator for delivering data in digital form to an installation via a telephone system, comprising in combination: a. acoustic signal-producing means responsive to electrical signals; b. mounting means carrying said signal-producing means and arranged for attaching said signal-producing means to the mouthpiece of a standard telephone so that said producing means are in acoustic communication with the mouthpiece microphone; c. signal-generating means for generating electrical audio frequency signals and for coding these signals according to the information to be delivered, said generating means being connected to said signal producing means for delivering the coded audio frequency signals to the input of said signalproducing means, said signal-generating means comprising: oscillator means for generating audio frequency signals at two different fixed frequencies; switch means connected to said oscillator for controlling the delivery of such audio frequency signal to said acoustic signal producing means; and coding means connected to control the opening and closing of said switch means for intermittently applying such audio frequency signals to said signal producing means according to a predetermined code, the code produced by said coding means for each bit of information being constituted by periodic pulses; said switch means being arranged for delivering a signal at one of the two fixed frequencies for the duration of each such pulse, for delivering a signal at the other of the two different frequencies during the periods when no such pulse is present, and for interrupting the supply of operating power to said oscillator means when said coding means are inactive; d. an auxiliary oscillator for generating an audio frequency signal at a further frequency; e. further switch means for connecting the output of said auxiliary oscillator to said signal-producing means; and f. switch-operating means connected to said further switch means for delivering the signal from said auxiliary oscillator to said signal-producing means to signal the end of data transmission.