60Hz time base signal generating circuit

The circuit in Figure 1 is a 60Hz digital clock time base circuit consisting of a 12-bit binary serial counter/frequency divider CD4040 and a six-phase inverter CD4069.

In the circuit, gates I and II of CD4069 form a crystal oscillator with an oscillation frequency of 32768Hz. Its output is shaped by gate III of CD4069 and sent to the end of CD4040. The output of CD4040 is divided by diodes VD1~VD3 to a frequency division coefficient of 21+25+29=546. After frequency division, a 60Hz clock signal can be output at the output end Q9 to supply the digital clock integrated circuit.

Figure 2a is another 60Hz pulse generating circuit. It consists of integrated circuit CD4060 and crystal oscillator with a resonant frequency of 30720Hz. CD4060 is a 14-bit binary serial counter, divider and oscillator. CD4060 is divided into two parts, one of which is a 14-level counter/divider with a frequency division coefficient of 16~16348; the other part can form an RC oscillator with external resistors and capacitors, and can also form a high-precision crystal oscillator with an external crystal. This circuit uses an external 30720Hz crystal oscillator to form a crystal oscillator. After the oscillation signal is divided 9 times inside CD4060, an accurate 60Hz frequency signal (30720÷29=60Hz) is output at the Q9 terminal.

When this circuit is used with a dual-negative digital clock, the circuit in Figure 2b can be used for polarity conversion. VT1 and VT2 use NPN transistors, such as 9013, 8050, etc. In the figure, terminal A is connected to the positive power supply, and terminal B is connected to the negative power supply. When this circuit is used with a dual-yang digital clock, VT1 and VT2 use PNP transistors, such as 9012, 8550, etc. In the figure, terminal A is connected to the negative power supply, and terminal B is connected to the positive power supply.

Figure 3 is a 60Hz pulse generator circuit composed of 60Hz pulse generator dedicated integrated circuit MM5369 (8-pin DIP package) and crystal oscillator with a resonant frequency of 3.579545. It is often used to provide 60Hz frequency with digital clock. After the oscillation signal is processed by the internal frequency division of MM5369, it is output from pin 1 and the frequency is quite stable. The circuit is powered by a 6~12V power supply. When the power supply voltage is lower than 6V, its working reliability deteriorates. In special cases, the resistance value of R3 in the circuit can be changed to about 100 ohms, which can reduce the normal working voltage of the circuit to 4.5V.

The above two circuits are applicable to the whole circuit with negative grounding, and are also applicable to the circuit system with positive grounding, and can be used flexibly during design.

Figure 4 shows a 60Hz clock circuit composed of two CMOS integrated circuits and a quartz crystal. The quartz crystal and CD4060 form the oscillation and frequency division parts, and BG1 and CD4017 form the counting and distribution parts. The square wave signals of 1024Hz and 4Hz are output at the 5th and 2nd pins of CD4060 respectively. The 1024Hz signal is input to the 14th pin of CD4017 as a clock pulse. The 4Hz signal and the signal assigned to the 11th pin of CD4017 form an "OR gate" signal and are then input to the 15th pin of CD4017 as a reset signal. Within the 1/4 cycle of the 2nd pin of CD4017, when the level is high, CD4017 is reset; when the level is low, CD4017 receives 128 pulse signals, and CD4017 is reset once for 9 pulse signals, so that only 15 pulse signals are assigned to the 2nd pin of CD4017. A total of 60 pulse signals are assigned to the 2nd pin of CD4017 within 1 second, thereby obtaining a practical clock 60Hz standard time base signal.

To calibrate the quartz oscillation frequency, you can use a frequency meter to measure the 9th pin of CD4060, which should be 32768Hz. If it deviates, you can fine-tune the variable capacitor to correct it.

Figure 5 is a 60Hz time base signal generator composed of a CD4060. Compared with the previous ones, it is the most practical time base signal circuit.