Many electronic projects call for a timebase generator, accurate to a second or so. One way of producing this is with a microcontroller, quartz crystal, and some software. But a far cheaper and simpler approach is to recycle an old analog quartz clock. After investigating a number of clocks the author discovered that they all use the same drive method: a tiny solenoid coil is pulsed by a current that reverses direction once a second.
In the module illustrated this coil is connected between pins Pulse1 and Pulse2. Most of the time both pins are ‘high’ at supply voltage but every second the clock electronics pull the first one and then the other of the pins down to the ground for about 25 ms.
We need just five additional components to complete the circuit (see diagram). When either of the pulse pins is at ground potential, the corresponding PNP transistor conducts. Once a second a narrow pulse is produced, which is ideal for our own digital circuitry. The author himself uses one of these clock modules as a timebase for a data logger with excellent results. Although the clock originally used a 1.5 V supply, this new arrangement works fine with a 3-V lithium battery. After three months of using the same battery, there have been no problems whatsoever.
