Quartz Crystal Windup Wall Clock
Posted on Feb 26, 2013 9063
Under: Clock Circuits
Last year, I found a 31 day pendulum wall clock (dissambled) in a box of parts at a swap meet and decided to try and put it together and regulate it with a quartz crystal oscillator. The escapement part that rocks back and forth and drives the pendulum was missing and had to be made from a couple razor blade pieces and heavy copper wire. The razor blade escapement worked well but only allowed the movement to advance as the pendulum swung, and would not sustain the pendulum motion by itself. But this wasn't a problem since the quartz crystal divider circuit provides energy to the pendulum with an electromagnet to keep it swinging with only a 5 second error per day.
Click here to download the full size of the above Circuit.
The 31 day mainspring was included, but I wanted to use a weight and drive wheel in place of the spring. The clock movement is made in Korea by "Sau Jin LTD" "Dae Woo CO LTD" and has no jewels. It measures 4.5 inches diameter by 1.5 inches deep plus 1.5 inches for the hands and drive wheel shafts, so the clock face and hands are about 3 inches from the wall. The pendulum period is close to 53.4 complete swings per minute. Can't figure out why that particular period was used. I have seen similar movements on ebay. The clock pendulum was made using a 10 inch, 3/16" wooden dowel with a strong magnet attached to the bottom and a small weight near the top to adjust the period close to 53 beats per minute. The circuit board and electromagnet to drive the pendulum are located on a small shelf (not shown) and positioned so the pendulum magnet swings close to the stationary electromagnet and receives a small pulse on each swing to sustain oscillation. The pulse duration is about 5% of the pendulum period and a LED is used to indicate the pulse output. The clock starts fairly easily by releasing the pendulum near the magnet when the LED flash is observed. Quartz Crystal Synchronizing Circuit: The synchronizing circuit that produces a short magnetic pulse to keep the pendulum in near perfect time was made using a crystal oscillator and binary counters to generate a 60mS pulse at the required rate of...