GB1375844A - - Google Patents

Abstract

1375844 Photo-electric control of display brightness CENTRE ELECTRONIQUE HORLOGER S A 10 Oct 1971 [30 Oct 1970] 47044/71 Heading G1A [Also in Divisions G3 and H2] In an electronic timepiece having an oscillator, a counter, and a display wherein selected electroluminescent elements are illuminated via a decoder circuit, a photovoltaic battery is arranged to act as the sole energy source for the display when ambient illumination exceeds a threshold level and a non-photovoltaic battery provides additional power for the display below this threshold level. Fig. 5 shows an arrangement using a photoelectric battery 46 to charge a capacitor 47 supplying energy to luminescent diodes 63 of the display. The display is controlled by electronic switches 66 triggered by decoder 67 in response to the output of oscillator 54 and counter 55. As long as the voltage on the capacitor 47 exceeds that of an upper reference source 51, the output N 1 of comparator 50 is unity and hence signal N 1 , being zero, keeps gate 61 closed and switch 65 open. No power is therefore drawn for the display from a capacitor 56 charged by chemical battery 53. If the leval of ambient illumination falls so that the signal N 1 changes to unity, the gate 61 and thus the switch 65 fall under the control of a modulator 59 which operates in response to a signal E from an ambient illumination detector 60 and a signal H 1 from the counter 55. As long as the voltage on the capacitor 47 is still above that of a lower reference source 49 so that the output N of comparator 48 is unity, switch 64 is operated in response to a further signal H from the counter fed to an asynchronous sequential logic circuit 52 so that some power is still drawn for the display from the photo-electric battery 46. The battery 53 supplies additional power so that the mean display brightness is varied and visibility is ensured over a range of ambient illumination. If this illumination falls further so that the comparator output N also changes to zero, the switch 64 remains permanently open, disconnecting the photo-electric battery 46. The battery 53 continues to supply the display through the switch 65 which is controlled so that the brightness is reduced with that of the ambient illumination down to a minimum threshold brightness. The display may be pulsed at intervals which are short compared with visual persistence of the human retina, or alternatively the minutes display can be pulsed at one second intervals. In a simpler arrangement, Fig. 4 (not shown) the photo-electric and chemical batteries (32, 44) are connected by a resistor (45), and a storage capacitor is connected at the output of the photoelectric battery. The chemical battery supplies make-up power to the display until a high level of illumination is reached above which it is recharged. At very low light levels, the photo-electric battery may be disconnected.