Patent GB-1417241-A (GB)
Title: Automatic telephone dialling device
IPC: H04M1/2749
Filed: 1973-01-09
Abstract: 1417241 Impulse transmitter J ZOCK 9 Jan 1973 [10 Jan 1972] 1129/73 Heading H4K An automatic dialling machine incorporates means for repeatedly calling a same number in the event of failure to receive ringing tone within a preset period following transmission of the number.  Up to twelve digits of a wanted number are inserted in binary fashion into a 16-place 64-bit memory 12 in response to actuation of keys of a keyboard 34. A key 36 and/or 38 is then depressed to insert into the remaining memory places the tally number of repeated callattempts that-are to be made in reaching this number. As each digit is entered (and also as it is subsequently outpulsed) it is set-up on a 12- place visual indicator that utilizes 7-segment display characters. Start button 42 may then be operated. Dial tone is detected with the aid of device 14 which incorporates an active filter, an operational amplifier, a precision rectifier and a phase-lock-loop detector (Fig. 16). The device monitors the line for a 400 Hz frequency and responds if this persists for a few milliseconds. It counts the number of pulses from a pulse generator 32 which occur during a three-second period in coincidence with the line frequency signal.- Since every tone:-busy, dial ringing &c., produces a different pulse count in such a period, a logic circuit can easily sort the tones. If dial tone is not detected within 10 sees. the machine makes a new call attempt by unlooping and then relooping the line. If tone is detected, the output from a 10 i.p.s. pulse generator 32 is used to operate an impulsing relay in line interface circuit 28 (Figs. 12, 17, not shown). At the same time the number of pulses generated is compared at 44 with the first digit in store whereby, when coincidence is reached, impulsing is stopped and a one-second interdigital pause is provided. This repeats for every digit. During impulsing the tone detector circuits are isolated from line by contacts of a guard relay. When the number is fully transmitted, a 10-25 sec. period is timed after which if no tone at all has been received the machine recycles. If a busy tone occurs, the machine recycles after a further 6-90 sec. period as selected by selector 46. Just prior to each recycling the current tally number which is stored in counter 18 is compared with the preset tally number in store 12 to see if a new call attempt is to be made. If ringing tone is received this activates an audio generator 24 to provide an audible output. The machine cuts-off if the machine operator does not lift his handset within 30 sees. of receipt of ringing tone. If the handset is lifted at any time a relay operates to connect it to line in place of the machine. The latter's circuits are reset except for the current tally count whereby it can continue to dial up to the preset number of attempts when automatic operation is restored. More than one number may be stored in the machine. A data modem may communicate automatically with a computer with the aid of the dialling machine. Line continuity and data pulse amplitude are constantly monitored using another active filter device tuned to 800 Hz so as to ensure security of transmission. Lifting of the handset is not permitted to interfere with data sending. When the machine is installed in a PBX provision is made for the detection of local and exchange dial tones preceding and following respectivley the transmission of the initial digit.