Many people love large clocks, especially the analog kind with real hands that go round and round. They not only have a practical value, they can be a beautiful decorative piece in the home. But since they are often mounted high on a wall where access to the means for setting them is difficult, they can be a pain in the neck twice a year when daylight savings time comes and goes. Some owners having knowledge and familiarity with radio controlled clocks are often tempted to try upgrading their treasured large clock by replacing whatever kind of movement it uses with a battery powered radio controlled movement. This often leads to disappointment and frustration because it is not as simple as it sounds. To understand the problem you have to be aware of a fundamental difference between the construction of a standard quartz movement and an RC quartz movement.
Ordinary battery operated quartz clocks haven't changed much in 50 years. They use molded plastic gears many of which have tiny teeth not much larger than this "-". The motor is a special stepper motor that rotates one half revolution when it receives a brief pulse of one polarity, then completes the full revolution when it receives a pulse of the opposite polarity. Pulses are delivered at one second intervals, and there's a 30-to-1 gear reduction between the motor and seconds hand shaft. So the seconds hand steps around the dial in abrupt 1-second jumps rather than smoothly. An additional 60-to-1 gear reduction drives the minute hand one revolution per hour, It's actually stepping too, but the steps are so imperceptibly small that for all practical purposes the minute hand is rotating smoothly.
Early radio controlled clocks used movements identical to this, to which were added sensing devices for knowing when the hands were on 12:00:00, a 60 KHz AM radio receiver, a few miscellaneous switches (such as a time zone switch), and a microprocessor to tie it all together. But about ten years ago, manufacturers of RC clock movements all began designing their movements to use two motors with independent gear trains, one for driving the seconds hand at one step per second, and the other for driving the minute and hour hands at one step every ten seconds. Without going into technical details why they changed to two motors, suffice it to say that it was done so the clock can automatically set itself faster when it first starts up. But this little design "improvement" has a devastating effect on the ability to use a radio controlled movement for a large clock.
Instead of the minute hand shaft having plenty of drive power due to being geared down 1800-to-1 from its stepper motor, in a dual motor design the gear reduction is only 180-to-1. This requires the tiny flea-power motor to provide ten times more torque to rotate the minute hand, the longest and heaviest of the clock. Each drive pulse to the minutes motor must cause the minute hand to jump forward a full degree, which is an appreciable distance on a large diameter clock. So a large clock often fails to complete a minute hand step, and sometimes just stalls completely.
Klockit, the major distributor of RC clock movements in the U.S., states that their RC movement should be used only for clocks up to 10 inches in diameter. They also recommend that for clocks larger than 10 inches you should use one of their "high torque" movements. That's very discouraging for large RC clocks because nobody in the world makes a high torque movement that is radio controlled. I've considered trying to drive a high torque movement with signals from an RC movement but the dual motor drive signals are totally incompatible. I've also tried to fabricate 15 inch long hands that are extremely light weight and balanced, but they ruin the classic look of a very nice clock. There is no simple solution to this problem at present.
This proposal is for the design of a processor control that can be used with any standard high torque quartz movement to give it the two most important performance features of a radio controlled clock, namely perpetual display of accurate time, and automatic adjustment for daylight savings time. The control is simplified by avoiding completely the most difficult task of a radio controlled movement, that of automatically setting the display on startup.
The control relies generally on the crystal controlled accuracy of a high torque movement, and adds or subtracts drive signals to the motor only when broadcast time data indicates the clock needs a correction because it is running a few seconds fast or slow. When the control decodes a radio broadcast, it saves the date/time and starts counting drive pulses to the motor. When it decodes another broadcast it calculates the elapsed time in seconds between that and the previous broadcast, and compares it to the number of pulses the motor has received during that time interval. If the numbers don't agree, the error is corrected by either adding or skipping a few pulses to the motor. The process of counting pulses and comparing successive broadcasts is repeated continually to keep the clock displaying precise time.
There could be commercial value in this project, but I have absolutely no interest in that. More details for anyone seriously interested in considering joining my one-man team.
Contact me either by replying to this post or directly at tomytyler[at]comcast[dot]net.