Patent GB-1209557-A (GB)
Title: Improvements in or relating to apparatus for recording indicia on a recording medium and a magnetic transducer for use in such apparatus
Inventor: WOLF EDGAR
IPC: G11B5/127
Filed: 1968-05-27
Abstract: 1,209,557. Magnetic heads; magnetic tape data stores. DIGITRONICS CORP. 27 May, 1968, No. 25231/68. Headings G4C and G5R. [Also in Division H4] A magnetic transducer comprises an isotropically magnetizable support consisting of two portions 163A, 163B carrying, respectively, a set of first conductors 22-1 to 22-P, and at least one second conductor 22S1, transverse to and spaced along a tape 46 and selectively energizable to transduce corresponding discrete areas of the tape. The conductors lie in grooves in two ferrite blocks, the second conductors 22S1-22S6 being staggered relative to the first and being energized together to record a sync. or "sprocket" track. The head is used to record binary data stepwise in a reel-to-reel magnetic tape cartridge by depressing appropriate keys of a keyboard, then, on a separate machine, transmitting the data as a waveform switching between two tones over a normal telephone line upon receipt of a valid call. Recording (Figs. 1, 3, not shown).-The tape is first advanced to give an unrecorded length by momentary depression of a switch (34). The information is converted to binary form in keyboard/encoder unit (18) which triggers local transistorized switching circuits (126-1) to energize appropriate windings 22-1, 22-2, 22-4, 22-8 and parity winding 22-P of the recording head 22, simultaneously via OR-gate (140) energizing the series-connected sprocket windings 22S1 to 22S6. Head 38 erases previous recordings. A stepping motor (26) drives capstan (50) coupled by a belt (52) to take up spool (42) to feed the tape 46 which is tensioned by spring-loaded roller (54). After recording, a motor (32) drives the supply spool (44) to rewind the tape. Playback (Fig. 2).-The cartridge is placed in a playback machine 64 of similar construction and under the control of a transmitter 66. When a subscriber at 72 makes a call to telephone 88, ringing of the bell is sensed at 94 whereby the transmitter opens the cradle switch 104 via solenoid 108 and if the characteristic tone is received at microphone 98, the motor 76 is driven to feed the tape continuously past a twin track playback head 74, the serially read data then being NRZ encoded in transmitter 66 and transmitted via speaker 92 and handset 86 as a waveform shifting between two tones. Operation.-The playback circuitry (Fig. 7) is " set " by momentarily closing switch 65 to enable AND-gate 210 and de-energize relay 205 controlling the tape drive motor 76. Ringing of the bell is picked up by microphone 94 to set bi-stable 214, thereby closing cradle switch 106 via solenoid 108 and initiating delay 222 which times out if no tone is received during a given time interval to reset bi-stable 214. If a tone is picked up by microphone 98, bi-stable 200 is reset to energize relay 205 and so long as data is transmitted, pulses fed via line 240 to delay 242 maintain the control circuit 182 in this state. "Sprocket" signals read by head 74A set bistable 258 to enable AND gates 264, 268, thereby allowing passage of data bits from head 74B and sprocket bits to bi-stable 278 whose output is fed through monostables 288, 296 to OR-gate 286 whose other input receives the sprocket bits on line 284. The OR-gate output is fed through inverter 304, flip-flop 308 and voltage controlled astable 312 to produce an output at speaker 92 consisting of one or other of two frequencies. Absence of sprocket bits from head 74A allows delay 254 to clear bi-stables 258, 278, and automatically stops the apparatus.