Back in the late 1970's I built a clock with 12 volt AC input power supply. I installed a small 12 volt rechargeable battery on the clock after the rectifier bridge and smoothing capacitors ( I used tantalum capacitors) for backup of the clock IC. I built a small circuit using a reed relay powered by the AC input set up so that when AC was lost the relay opened and turned off the clock display. Then I built the 1 CPS circuit with a MM5369 IC and a color burstt crystal at 3.579 MHz ( a large size crystal common in all color televisions at the time but still commonly available) . The IC divides this down to 1 CPS. With a high quality air variable capacitor as the trimmer capacitor, I adjusted the clock against short wave radio receiving WWV and over a few years I was able to adjust the time accuracy to less than a second off per month ! It just got to be too long a wait to adjust the time as it became more accurate. The complete circuit is easily found using Google.
Phil
---------- Original Message ----------
From: gregebert <[email protected]>
Date: September 5, 2018 at 5:02 PM
Lessons-learned for future clock designs......I've converged on using a RasPi + DS3231 for all current and future designs, so I never need to set the time for power-failure, daylight savings, etc.--
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