cheap seconds

Those of you who study advertise- ments will have noticed that minia- ture crystals for watches are much cheaper nowadays. These crystals are almost invariably tuned to 32.768 kHz, and for a good reason — it is quite easy to derive a 1 Hz signal from this frequency, since it a simple power of two (215 ). Add to this knowledge the fact that the IC type 4060 contains a 14-bit divider stage and oscillator section, and you can put two and two together ... The watch crystal is eminently suitable as frequency- determining element for the oscil- lator. If the maximum division ratio of the divider stage is used (2 14 ), the result is a 2 Hz output. Getting close ... To bring this down to the mother of all timing intervals one-pulse-per-second, a single flipflop must be added; half of a 4013, say. The output from this flipflop is a 1 Hz signal, swinging between 0 V and positive supply. Life would be beautiful, if it weren"t for component tolerances. Crystals need trimming — which is wh...