Patent GB-1487062-A (GB)
Title: Master/slave clock system
IPC: G04G9/00
Filed: 1974-09-03
Abstract: 1487062 Master/slave clock systems EP JORDAN 3 Sept 1974 [4 June 1973] 26602/73 Heading G3T In a master slave clock system for distributing time of day and/or timed alarm signals from a central transmitting location to one or more remote receiving locations (e.g. hotel bedrooms), a transmitter sends successive coded pulse trains and each receiver at the remote locations has pre-setting means for selecting a particular coded pulse train exclusive to a particular time of day and means arranged to operate an alarm when the occurrence of the particular coded pulse train is detected. Reset means reset a pulse converter in each receiver after reception of each pulse train. The transmitter and receivers may be linked by light beam, radio or line. Each receiver may also include a time of day indicator. As shown, Figs. 1, 1A, the transmitter includes pulse converters 5, 15 and each receiver includes a respective pulse converter 19 similar to 5 and 15. Converter 5 comprises a Schmidt trigger 6 and four shift registers 7 connected to output terminals 8. A master clock 2 closes a switch 3 at 5 minute intervals starting at 12.00, to apply D.C. trigger pulses to converter 5. Successive input pulses result in successive different combinations of output potentials from the converter 5 to terminals 8 which are connected to twentyfour transistor switches 9. There are 144 different possible combinations, a respective one for each 5 minute interval, and for each combination a respective pair of transistor switches 9 (one for minutes, one for hours) is activated to energize a respective relay 10 controlling a further relay 13. Successive pulses from a 400 Hz pulse generator 16 to the converter 15 causes successive different combinations of potentials at the converter outputs 14 and at a more rapid rate than the outputs of converter 5. The relay 13 via contacts 13a is arranged to interrupt the pulse feed to converter 15 except when any of switches 9 is actuated. The correspondence between converters 5, 15 is such that the pulse gen 16, before it is interrupted, feeds to converter 15 a number of pulses equal to the total number so far fed into converter 5 by the master clock switch 3. The pulse gen. 16 therefore feeds a series of pulse trains, at 5 minute intervals, of successively increasing numbers of pulses (i.e. the series - 1, 2, 3 ..... 144) to the converter 15, the latter being reset between successive pulse trains by interruption of its power supply through a switch 17. At the receiver, selector switches 1a, 1b are set by the room occupant, to the desired alarm call time. When that time occurs a particular combination of output potentials will be produced by converter 19 at its terminals 20, the converter 19 being arranged to produce successive different combinations of output potentials in response to reception of successive different pulse trains fed thereto via a line 18 from the transmitter, and will actuate a transistor switch circuit 22 to cause an alarm signal. After each pulse train received the receiver converter 19 is reset since otherwise successive trains would be added to each other, the power supply to 19 being interrupted to reset it when the supply to converter 15 is interrupted by the switch 17.  The or each slave station may be portable, e.g. a wrist watch.