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.
Utilizing Clock Module’s Coil Connection
In this configuration, the coil is intricately linked between pins Pulse1 and Pulse2 within the illustrated module. Typically, both pins maintain a ‘high’ status, aligned with the supply voltage. However, every second, the clock electronics systematically pull one pin down and then the other, grounding them for approximately 25 ms.
Efficient Circuit Expansion
To augment the circuit, a mere five additional components (refer to the diagram) are necessary. Whenever either of the pulse pins is grounded, the corresponding PNP transistor conducts. This setup generates a precise narrow pulse every second, ideal for various digital applications. The author, in fact, employs one of these clock modules as a timebase for a data logger, yielding exceptional results. Originally designed for a 1.5 V supply, this revised configuration seamlessly operates with a 3-V lithium battery, demonstrating impeccable performance over three months of continuous use.
Understanding PNP Transistors: Versatile Current Control Devices
PNP transistors, structured with one n-type material doped between two p-type materials, serve as devices regulated by current. The emitter and collector currents are meticulously controlled by a small base current. Within this design, two crystal diodes are interconnected back-to-back with the PNP transistor.
PNP Transistors in Diverse Applications
PNP transistors find utility as current sources, directing current out of the collector. They function aptly as switches and are integral components in amplifying circuits. Moreover, PNP transistors are indispensable when the objective is to deactivate a component via a button press. This specific transistor type features a unique configuration where one n-type material is doped with two p-type materials, enhancing its applicability across various electronic contexts.