Many oscillator frequencies can be divided down to control a clock here, the crystal’s frequency is 4.194304 MHz = 2 22 Hz. The transistor - an MPF-102 or similar FET - is used in a crystal-controlled oscillator. The time base consists of one transistor and two integrated circuits. In a microprocessor based clock, these functions are almost all carried out by the microprocessor here, they are distributed among nine integrated circuits and a few transistors. Lastly, a power supply provides the power that the other parts require. Driver ICs decode these outputs to drive the displays, which show the time. Counters count the cycles of the time base’s signal and generate outputs that represent digits. That signal is derived either from the 60 Hz line frequency or - as here - from a crystal oscillator. The overall design of the digital clock.Ī time base provides a signal of fixed frequency whose cycles are counted to mark the passage of time. StructureĪ digital clock consists of four parts as Figure 1 illustrates.įIGURE 1. Two pushbutton switches allow the minutes and hours to be set, and the whole thing is powered by a small wall supply. Two more LEDs indicate AM and PM alternately. The clock presents the time on a four-digit display - hours and minutes - with the colon between blinking once each second. The most complicated ICs in it contain several flip-flops and some additional logic. It is a straightforward 12 hour clock with CMOS integrated circuits and seven-segment LED displays. This project lies between these extremes, toward the early end chronologically. A novel example of this kind of clock appeared in the March 2014 issue of Nuts & Volts. At the other extreme are microprocessor based clocks with many thousands of circuit elements compressed into one or a few integrated circuits. At one extreme are clocks made entirely with individual transistors, resistors, and other discrete components like the aggressively retro kits produced by KABtronics and described in these pages a few years ago. There are digital clock projects and there are really digital clock projects. » Skip to the Extras A clock project using CMOS logic and seven-segment displays.
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