Design of a Digital Clock 30, How to Make a Digital Clock?

The basic working principle of a digital clock:

Digital clocks have been welcomed by people for their intuitiveness in displaying time and accuracy and have quickly entered thousands of households. As a timekeeping tool, the basic component of the digital clock is inseparable from the counter, which completes the predetermined functions under the control of the control logic circuit.

1), time-based t generation circuit:

The pulse generated by the crystal oscillator with a very stable frequency is shaped and stabilized by the circuit to generate a very stable counting clock pulse with a frequency of 1Hz.

2) Control logic circuit:

Generate time modulation, division signal and bit selection signal.

The generation of time adjustment and division signal: it can be seen from the counting process of the counter that when the second counter (60 system) counts to 59, and then there is an empty pulse, the second counter is cleared to zero, and a new round of counting is started, and the carry is used as the counting pulse of the sub-counter, so that the sub-counter count is increased by 1. Now let's change the circuit a little:

The carry pulse of the second counter and the pulse signal of a frequency of 2Hz are connected to the two data input terminals of a 2-to-1 data selector at the same time, and the bit-select signal is connected to a pulse key switch, when the key switch is not pressed down (i.e., 0), then the data selector sends the carry pulse of the second counter to the minute counter, and at this moment, the digital clock works normally; When the key switch is pressed down (i.e., 1), the data selector will use another 2Hz signal as the counting pulse of the sub-counter, so that the counting frequency is accelerated, and when the correct time is reached, the key switch is released, so as to achieve the purpose of time adjustment. The same is true for adjusting the time of the hour.

3), counting display circuit:

It is composed of a counting part, a data selection eraser, and a decoder, which is the key part of the clock.

Counting part: consists of two 60-base counters and a 24-base counter, wherein the 60-base counter can be composed of a 6-base counter and a 10-base counter; The decimal hour count in base 24 can also be obtained with a base 6 counter and a base 10 counter: when the counter counts to 24, the "2" and "4" are cleared at the same time, and the base count can be realized.

Data selector: 84 inputs and 14 outputs of multiplex data selector, because 8 digital tubes were used in this experiment (two were used to generate the isolation symbol '—'

Decoder: Seven-segment decoder. The decoder must be able to interpret '—' from the truth table of the decoder in Experiment 2

The 8421bcd code of the letter F is "1111", and the decoded is "1000111", and now if only the middle horizontal of the letter F is translated, it should be "0000001" after decoding, so that the display on the digital tube is "—".