A low-cost 1Hz time base for digital clocks, timers etc. is presented here. Besides its simplicity, the specific clock has remarkable precision. The circuit is built around U1 (4060) and U2 (4027) integrated circuits, a 32.768KHz crystal, some resistors and capacitors.
U1 is a 14-bit binary ripple counter and has an internal oscillator. The oscillator runs at 32.768KHz. At pin 3, there is a clock signal of 2Hz, which is derived from the main oscillator signal being frequency-divided by 214 (16384).
The 2Hz signal is passed to the clock input pin of U2, which is a dual JK flip-flop, and it is furthermore frequency-divided by 2. From the Q2 output (pin 1 of U2) we get 1Hz.
We use a quartz type crystal of a standard value (32.768 KHz) which is normally used in electronic watches. C2 is used for micrometric adjustment of the oscillator frequency, so that it can be calibrated exactly to 32.768 KHz. Calibration can be done by using a frequency meter.
The clock generator which is described here is very stable and more accurate than many other types of simple clock generators. Its stability is mainly depended upon crystal’s quality and upon changes of the ambient temperature.