(1) The main circuit consists of a second signal generator, a \"hour, minute, second\" counter, a decoder and a display, a calibration circuit, etc.
(2) Second signal generator is generally realized with quartz crystal oscillator extra frequency.
(3) The decoding circuit sends the output state of the hour, minute and second counter to the seven-segment decoder, which is displayed through the six-digit LED seven-segment display.
(4) The timing circuit is used to proofread the time, minute and second display numbers.