This invention is directed to a small-sized electronic digital display timepiece including a calculator, and in particular to improved circuitry for simplifying and reducing the size of a keyboard for a calculator to render same more particularly suited for use in a small-sized electronic timepiece.
The development of small-sized integrated circuitry has resulted in the production of small-sized desk-top and hand carried calculators at sharply reduced prices. The portability and reduced cost of such small-sized calculators have contributed to their immense popularity. In furtherance of this trend toward reduced size and portability, calculator circuits of a size small enough for incorporation into electronic digital display wristwatches are readily available through application of large scale integration techniques. However, the reduction in the size of the calculator in order to enable same to be utilized in an electronic wristwatch has presented certain problems not heretofore experienced in desk-top calculators.
The development of said integrated circuit techniques have enabled the calculator circuitry to be easily incorporated into the small-sized watch cases. However, because the input circuitry of conventional calculators require a keyboard having at least 16 keys, each key being of sufficient size to allow the keys to be displaced by the fingers of the operator, the size of the keyboard has rendered the use of such calculator circuitry in an electronic timepiece less than completely satisfactory. Accordingly, a keyboard which is particularly suitable for use in a desk-top or hand carried calculator is not practical when utilized with a calculator circuit incorporated in an electronic timepiece. Accordingly, a calculator including improved input circuitry to effect a reduction in the number of keys and hence the size of the keyboard is required in order to effect an improved calculator and render same practical for use in an electronic wristwatch.