Fig.1: a clock stepper motor uses a multi-pole permanent magnet rotor which rotates inside a circular gap in a soft-iron stator. It's made to step in the same direction by reversing the polarity of the current pulse at each step.
If you built the GPS-Based Frequency Reference described in the
March-May 2007 issues, you’ll know that it provides a continuous readout of
"Universal Time Coordinated" (UTC) on its LCD. This time is derived directly
from the GPS satellite system and is therefore very accurate.
In practice, it’s not all that difficult to mentally convert
UTC into local time. In most cases, you simply add or subtract a certain number
of hours, depending on the nominal longitude of your local time zone and, of
course, your time of year. For example to convert UTC into Eastern Australian
Standard Time, you simply add 10 hours, or 11 hours during the summer months
when we’re on "Summer Time" (daylight saving). So 05:15:00 UTC becomes 15:15:00
(3:15pm) EAST, or in summer 16:15:00 (4:15pm).
That’s all well and good but most people would find a direct
readout of their local time a little more useful. And that’s where this project
comes in. It uses the 1pps (one pulse per second) output from the GPS system to
drive a quartz wall clock. All you have to do is set the display for local time
at the start, after which the clock will be accurately controlled via the GPS
It turns out to be very easy to interface the GPS Frequency
Reference to a standard ‘analog’ quartz clock movement. First, you have to
remove the existing circuitry from the clock (usually just a chip and a crystal
on a tiny PC board) and bring out the connections to the clock’s escapement
coil. That done, the coil can be pulsed instead by the little driver module
described here. This driver module is small enough to fit inside the clock (next
to the movement) and gets its power from the GPS Frequency Reference, along with
the 1Hz (1pps) pulses.