GB1172946A - Code Converter - Google Patents

Abstract

1,172,946. Code converters. STANDARD TELEPHONES & CABLES Ltd. 15 Aug., 1968. No. 39007/68. Headings G4H and G4R. A code converter adapted to produce a fixed length parallel binary code output in response to a variable length input code group, comprises a binary shift register 3 and a binary counter 4, the successive bits being shifted in the shift register and counted by the counter, the last member of the group, which indicates the end of the group, being used to enable decoding gates 50 and also to reset the shift register and counter. The input may be from a microphone E, receiving spoken code elements similar to Morse, the short element being represented by the word " di " and the long element by the word " dar." The short intervals between elements are used to shift the elements with the register and to advance the counter. The longer interval indicating the end of the group is used to reset the shiftregister and counter and enable gates 50. The microphone is connected via an automatic gain-control amplifier and a band-pass filter to an envelope detector 11 which feeds a threshold circuit 12. The output of the circuit 12 is applied to an integrating bi-stable 13 which sets when the input signal lasts for longer than a predetermined time. An output from circuit 12 therefore gives an output on terminal B if it is a long code element and, via inverter 16, on terminal A if it is a short element. These signals are used to set or reset the shift register stages. The absence of a signal from circuit 12, via inverter 14, gives a " silent " signal on terminal C. This is used to step the register 3 and counter 4. A pause, i.e. the interval between letter groups gives a reset and read-out signal on terminal D as well as terminal C. The outputs from the register and counter are combined in gates 50 to give a parallel coded representation of the input signal. One of these gates responds to a special code to set trigger 58 and open gate 57 thereby enabling the circuit to operate. Instead of the circuit 1, a modification can be used in which the output of the envelope dector is applied with the original signal to a differential amplifier. The output of the amplifier is applied to a threshold circuit and thence via an inverter to an integrating bi-stable. The desired signals are derived from the output of the bi-stable. In another form (Figs. 3a, 3b, not shown), the circuit is designed to distinguish between three classes of sound (rather than two); frictive, voiced sound and silence.