Patent GB-1497085-A (GB)
Title: Display for electronic clocks and watches
IPC: A61M5/34
Filed: 1975-02-10
Abstract: 1497085 Electronic timepieces J ST CLAIR KILBY 10 Feb 1975 [11 Feb 1974] 5471/75 Heading G3T An electronic timepiece has a single circle of sixty LEDs (or alternatively liquid crystal elements) which are selectively activated to indicate the time in hours, minutes and seconds. The minutes are displayed by flashing the appropriate element at a repetition rate of 2/sec. The seconds are displayed by successively energizing display elements to advance at 1 sec intervals. The element in the appropriate hour position is continuously activated for one hour and then the element in the next hour location is activated Figs. 1 and 2 or alternatively all the elements may be successively activated, the hour indication being advanced each 12 minutes to simulate the analogue action of a hand. When the hour and minute indications coincide both the hour position element and the element or both elements immediately adjacent thereto may be flashed. In a further alternative arrangement, Fig. 6, the hours and minutes are displayed in different colours by LED's. In the timepiece, Figs. 1, 2, the 60 cycle mains supply is used as a timing source and as an energizing source, a rectifier 6 and voltage regulater 7 producing a 5 Volt supply. A Schmitt trigger 21 produces 60 pulses/sec in a line 38 to a chain of counters 23, 24, 40, 43, 44, 45, 46. For rapid setting purposes the trigger 21 is controlled by pulses from a UJ oscillator circuit 22, a switch 28 being closed for setting the minutes and a switch 30 closed for setting the hours. Counter 40, 44, 46 counts the seconds, minutes and hours respectively. Multi-plexers 57, 58 connect the tens of seconds, tens of minutes and hours outputs of the counters to a sector decoder 111. The six outputs of decoder 111 are connected respectively to the commoned anodes of ten LEDs in each of six sectors 129, 130 &c of the display 126, via a respective transistor 119-124. Since only two hours indications occur in each sector the three most significant bits of hours counter 46 (bits BCD) are connected through the multi-plexers 57, 58 to the decoder 111. The least significant bit A is used to determine which hour within the selected sector is to be addressed. Multiplexer 62 couples minutes or seconds BCD data to a digit decoder 106 the outputs of which connect to cathodes of the LEDs via respective connecting rings 140-149. To select the cathode of the appropriate hours indicator to be addressed, the bit A of the hours counter 46 is gated through NAND gates 94, 91 to outputs 140, 145 of digit decoder 106. The output of decoder 106 is inhibited by the output of a three-state counter 49 via gates 55, 75, 77 to allow the outputs of gates 91, 94 to determine the hour LED to be addressed. Each state of the counter 49 corresponds to one of three sources of information - secs, mins, hours and it is driven by an 1000HZ oscillator 50 which also applies clock-pulses via a NAND gate 53 to the clock input of the sector decoder 111. A coincidence comparator 95 detects when the hour and minute indicators are in the same location and the hour indicator is also caused to blink. A multi-vibrator 25 (2Hz) controls the duty - cycle of the minute indicating LED. In a modification Fig. 6, LEDs having a characteristic such that at one level of forward bias current the display is red and at a different level it is green, are employed so that hours and minutes can be displayed in different colours. During the minute display for instance, output from the counter 49 via gate 55 causes a transistor 340 to conduct, paralleling R341 and R342 whereby a higher level drive current is passed to the appropriate LED via the respective drive transistor 119-124. Fig. 5 (not shown) illustrates a modification using liquid crystal display elements. TTL, 12 L or CMOS integrated circuits may be used. The timepiece may be a watch, in which case a crystal controlled oscillator provides the timing reference frequencies 1Hz and 2Hz, instead of the mains.