Pin 1 and 40 of IC 3 are connected to f and e pins respectively of the ten-digit an hour of the alarm display (DIS 7) which is further connected to the anode of LED 1 and LED 2 as shown in the circuit diagram. IC 3 further divides it and a 1 Hz signal is obtained at pin 39 and given to LED 1 and LED 2 to blink for AM and PM. The f and e segment of DIS 7 are used to represent AM and PM respectively for the alarm time display.Ī crystal oscillator of 4.9152 MHz is connected to pins 10 and 11 of IC 4 as shown in the circuit diagram which divides the oscillating frequency by 16,384 times and a 300 Hz clock pulse is obtained which is further fed to IC 5 which divides 300 Hz clock pulse by 6 to obtain 50 Hz clock pulse and given to pin 36 of IC 3. As in hour display, only two segment b and c of the LED is used to display 1 in display 7 (DIS 7). The lower four 7-segment display is used to display alarm time. The upper 3-pair of display (DIS 1 through DIS 6) is used to display hour, minutes, and second, where to display 1 (DIS 1) of hours used only two segments (b, c) of the LED to display 1 when the hour display reaches 10 and above.
The output pin 4, 3, and 2 of IC 2 is connected to transistor T 2 through T 4 respectively to ground all the 7-segment displays. Timer IC NE555 is used here as a multivibrator which is further combined with CMOS decoder IC (IC 1) to switch the two push-to-on switches for second and alarm, output from pins 2 and 3 of IC 1 is connected to pins 31 and 32 respectively to switch second/alarm time display. The entire circuit of the Digital Clock Circuit with Second and Alarm Display is built around clock chip IC (IC 3) followed by CMOS decoder (IC 1, and IC 5), timer IC NE555 (IC 2), and 14-stage counter IC (IC 4). Circuit Description of Digital Clock Circuit with Seconds and Alarm Timer Display
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