Print out control circuit for telephone transaction system

Claim 1

A print out control circuit coupled to a telephone transaction system for sensing incoming signals and determining their validity comprising; a. a first filtering means including a high-pass filter and a low-pass filter connected to input terminals of the transaction system for separating applied alternating currents into two groups each having differing frequencies; b. a second filtering means coupled to the first filtering means and including a plurality of filter circuits each tuned to pass only a narrow band of frequency signals to their output terminals; c. a decoding means coupled to a timed actuating means and a print wheel assembly for sending a timed current pulse to the print assembly to print a symbol; d. a first verifying ''''AND'''' circuit connected to the first filtering means for producing an output signal only when a signal is received from both the high-pass and the low-pass filters; e. a series of second ''''AND'''' circuits each coupled respectively to the output terminals of the second filter circuits, said second ''''AND'''' circuits each including an ''''ENABLE'''' terminal which must be supplied with an operating voltage before a second ''''AND'''' circuit passes an output signal; f. a first Schmitt trigger circuit coupled to the first ''''AND'''' circuit for transmitting an output validity signal only when the signals from both filter circuits are greater than a predetermined amplitude; g. a delay circuit coupled to the first Schmitt trigger circuit for delaying the output signal from the first Schmitt trigger until both the signals from the filtering means have applied a continuous signal to the delay circuit for a predetermined time interval, said delay circuit including a chargeable capacitor, and a second Schmitt trigger circuit for generating a pulse when the capacitor voltage reaches a predetermined value; h. a bistable multivibrator coupled between the first Schmitt trigger and the delay circuit for storing the validity signal received from said verifying ''''AND'''' circuit to apply a stabilized voltage to the charging circuit; i. and circuit means connecting the second SchmitT trigger circuit to the ''''ENABLE'''' terminals of all the second ''''AND'''' circuits to permit the second ''''AND'''' circuits to transmit signals to the decoding means when the second Schmitt trigger circuit is actuated.