Electric timepiece with light responsive battery recharging

Claim 1

An electronic timepiece comprising photoelectric element means mounted on said timepiece for exposure to ambient light; a secondary Ni-Cd battery; means connecting said secondary battery to said photoelectric element means including semiconductor element means for preventing discharge current from said secondary battery to said photoelectric element means when the output of said photoelectric element means is small; a mechanical vibrator for providing time keeping means wherein said mechanical vibrator is a tuning fork and including a magnetic circuit; a two-terminal drive coil positioned for cooperation with said magnetic circuit for sustaining the oscillation of said mechanical vibrator; and drive circuit means coupling said secondary battery and said two-terminal drive coil for applying an oscillatory drive signal to said drive coil adapted to maintain the amplitude of said mechanical vibrator nearly constant when the voltage of said secondary Ni-Cd battery varies, said drive circuit means including a PNP and an NPN transistor, said two-terminal drive coil being connected between the respective collectors of said transistors, and means resistively coupling the base of each transistor to said two-terminal drive coil.