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Operation of a digital clock

Short answer

A digital clock receives a 1 Hz signal from a frequency divider (e.g., 50 Hz AC shaped and divided by 50). Seconds and minutes are mod-60 counters (mod-10 units, mod-6 tens). Hours use mod-10 units and flip-flop/reset logic for 12- or 24-hour display. BCD outputs drive 7-segment displays via 7447 decoders.

Explain the operation of digital clock with neat and clean diagram.

A digital clock displays hours, minutes and seconds in decimal digits. It works by counting a precise 1 Hz signal with a chain of mod-10 and mod-6 counters, decoding each counter's BCD output and showing it on seven-segment displays.

Block diagram

 AC 50 Hz -> [Shaper] -> [÷10] -> [÷5] -> 1 Hz
                                          |
   +--------------------------------------+
   v            SECONDS (00-59)
 [÷10 units] -----> [÷6 tens] -------+ 1 pulse/min
   |                   |             |
 [7447 dec]        [7447 dec]        |
 [7-seg disp]      [7-seg disp]      |
   +---------------------------------+
   v            MINUTES (00-59)
 [÷10 units] -----> [÷6 tens] -------+ 1 pulse/h
   |                   |             |
 [7447 dec]        [7447 dec]        |
 [7-seg disp]      [7-seg disp]      |
   +---------------------------------+
   v            HOURS (01-12)
 [÷10 units] -----> [tens FF] <--- reset/load logic
   |                   |
 [7447 dec]        [decoder]
 [7-seg disp]      [7-seg disp]

Operation

  1. Pulse shaping: the 50 Hz AC mains is stepped down by a transformer and converted to a clean square wave by a Schmitt trigger (wave-shaping circuit).
  2. Frequency divider: a ÷10 counter followed by a ÷5 counter divides 50 Hz down to 1 Hz (1 pulse per second). With 60 Hz mains a ÷60 is used; quartz clocks use a 32.768 kHz crystal and a 15-stage binary divider.
  3. Seconds counter: the units counter (mod-10) counts 0–9. Each 9 → 0 change clocks the tens counter (mod-6), which counts 0–5. At 59 → 00 the tens counter resets and sends 1 pulse per minute onward.
  4. Minutes counter: same as the seconds counter, giving 00–59 and 1 pulse per hour.
  5. Hours counter: a mod-10 units counter and a tens flip-flop with reset logic so that the hours go 01 → 12 → 01 (12-hour clock); a 24-hour clock clears at 24.
  6. Decoder/drivers: each BCD output drives a BCD-to-7-segment decoder (7447) that lights the right segments of each display.

The accuracy of the clock depends only on the accuracy of the 1 Hz time base.

✓ Answer checked by Claude Opus 5.5 (high effort)

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