This circuit provides a 50 Hz timebase signal that is independent from the power line frequency. It is designed to provide the 50 Hz signal for electronic circuits which function only with
this clock frequency (mostly circuits and electronic devices with european standards). It is popularly used for clock and timing applications. By carefully analysing the circuit diagram,
you can see that IC1 works as crystal controlled oscillator while IC2 functions as a 214 divider. The crystal frequency can be finely adjusted within 20 Hz range through the trimmer
Calibration is simple and can be done in two different ways. First method: if you have a digital frequency counter, connect it to pin 7 of IC1 (TEST output on the printed circuit board)
and adjust trimmer cap C2 until the frequency being displayed is 204.800 Hz.
Parts Placement Layout
External Wiring Layout
Now, if you don't have a frequency counter; just set the trimmer capacitor C2 at its middle position. This calibration method is of course not the most accurate but will be sufficient for most
applications. The output frequency, in this case, has a very negligible error of around 0.12 ppm.
This timebase source delivers three frequencies: 50Hz, 100Hz, and 200Hz. Now, if you want to divide further the output signal to obtain much lower frequencies, you can cascade additional
4013 flip-flop IC's at the output. Each 4013 has two integrated flip-flops.
You can power this circuit with voltages ranging from 5 volts up to 15 volts. This very wide power supply range is possible through the use of CMOS type ICs. The current consumption is
very low - a typical character of a CMOS - between 0.4 and 3 mA.
Electronic Circuits volume 1.0 - Circuit Nr. 84
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.