A paper on digital electricity

2. The purpose of curriculum design is 1. Around the content of curriculum design, cultivate students' ability to query relevant information and document retrieval; 2. Cultivate students' comprehensive application ability of what they have learned in the past; On the basis of understanding the knowledge in class, improve students' self-study ability; 3. Cultivate students to understand and gradually become familiar with the whole process of scientific research, and develop a good scientific attitude and pragmatic and rigorous work style; Cultivate students' ability of independent analysis and scientific research to solve problems; Course design content (1) Design requirements: ① Design a 24-second timer for basketball game with the function of displaying 24 seconds; ② The timer works in a decreasing way, and the time interval is 1s: ③ An external switch is set to control the timer to start, pause and reset; ④ Give an audible and visual alarm when it drops to zero: ⑵ Principle block diagram:

Course design purpose

Around the content of curriculum design, cultivate students' ability to query relevant information and document retrieval;

Cultivate students' comprehensive application ability of what they have learned in the past; On the basis of understanding the knowledge in class, improve students' ability.

Self-study ability;

three

Cultivate students to understand and gradually become familiar with the whole process of scientific research, and develop a good scientific attitude and a realistic and rigorous attitude.

Down-to-earth work style; Cultivate students' ability of independent analysis and scientific research to solve problems;

Course design content

( 1)

design requirements

：

①

Design a basketball game.

Second hand timer with display

A second timing function;

(2) The timer works in descending order, and the time interval is

③ setting external switch to control the start, pause and reset of timer;

(4) When the temperature drops to zero, an audible and visual alarm is given.

(2) Principle block diagram:

Include a second pulse generator, a counter, a decoding and display circuit, an alarm circuit and a control circuit (auxiliary time sequence control circuit).

And so on. The timing circuit decrements the timing every other time.

Seconds, the timer decreases.

Wherein the counter and the control circuit

The main part of the system. Counter complete

Second timer function, the control circuit completes the direct clearing and starting of the counter.

Counter, pause

Continuous counting, decoding display circuit display and turning off lights, timed time alarm and other functions. When the timer passes.

When the countdown time reaches zero (that is, the timing time has expired), the display screen displays.

At the same time, send out photoelectric alarm signal.

(3) Actual circuit diagram:

Second pulse

generator

counter

translate

show

Control circuit

report to the police

circuit

three

(4) unit circuit:

①

842 1BCD

Code addition counter module

Counter is an integrated circuit with summary scale.

74LS 192

The design is relatively simple,

74LS 192

The decimal system can be programmed as

Step lock counter, using

842 1

Code two

Decimal coding, with direct clearing, setting and locking counting functions.

draw

74LS 192

External pin and timing waveform diagram. In the painting; Be involved

cerebral palsy

、

cerebral palsy

They are counting down separately.

Pulse input (active rising edge)

lethal dose

It is an asynchronous parallel setting control terminal (active low).

Commander (commanding officer)

、

man

individually

Carry and borrow outputs (active low)

China Railway (China Railway)

Is an asynchronous zero clearing terminal,

D3-D0

This is a parallel data entry hall.

Q3-Q0

It's an output.

draw

1 74LS 192

External pins and timing waveforms

74 192

See the table below for the menu.

As shown in the figure.

Its working principle is:

while

lethal dose

= 1

CR=0

When,

If a clock pulse is added to the

cerebral palsy

End, and

cerebral palsy

= 1

The counter completes the counting function according to the preset number, and when the count reaches

nine

When,

Commander (commanding officer)

End distribution

Carry-down conversion pulse; If a clock pulse is added to the

cerebral palsy

End, and

cerebral palsy

= 1

, the counter is increased on the basis of preset number.

Counting function.

table

Two 74LS 192

function table

four

pass by

74LS 192

The 24-bit down counter is shown in the figure.

three

, the default quantity is

(

00 10

0 100

)

842 1BCD=

(

)。 Its counting principle is: only in the low position

When the terminal sends out a borrowing pulse, the high counter will do it.

Countdown.

When it is high,

The low counter is all zero,

and

When,

End of setup

2=0

The counter is set in parallel,

exist

build

Under the action of the input clock pulse, the counter enters the next cycle and counts down again.

draw

three

74LS 192

Twenty-four-bit down counter

② Clock module

In order to give the counter

74LS 192

Provide timing pulse signal

Let it count up.

This design adopts

555

compose

Multi-harmonic oscillation circuit based on

(

Namely a pulse generating circuit.

Its basic circuit is shown in the figure.

four

show

In ...

555

Pin diagram is as follows

2-5

show

pass by

555

According to its working characteristics and the calculation formula of output period

The pulse period it produces

for

：

T=0.7(R

+2R

therefore

We can calculate all the parameters and determine them by calculation.

R 1

take

20k

ohm

，R2

take

62k

ohm

Capacitance extraction

C 1

for

10uF

、

for

0. 1uF，。

In this way, we get a steady pulse.

Its output period is

second

draw

4 555

Multi-harmonic oscillation circuit diagram

③

Auxiliary timing control module

Basketball game

The function control of the second timer is realized by an external operation switch.

draw

five

As shown in the figure. change

Realization count

Equipment pause

Count control. while

For "

"When?

(

Zuohe

) ,

The second pulse signal from the second pulse generator is blocked.

Temporary counter

Stop counting

while

For "

"When?

(

The right combination

) ,

Control gate opening

The second pulse signal is sent to the pulse reduction input of the counter.

change

Counter-controlled

load

Asynchronous parallel set number control terminal

while

When closed

, load

′

Counter preset number

，L

separate

time

, load

′

= 1,

The counter is in counting working state. Counter clear pass switch

rare

control

，CLR = 1

Clear time counter

zero

，CLR = 0

time

The counter counts normally.

five

draw

five

Auxiliary timing control chart

④ Decoding display module

This module mainly includes

74LS48

Decoder and cathode seven segments

Light Emitting Diode(LED)

Show, through the counter.

For the decoder,

So as to realize a seven-segment cathode.

Light Emitting Diode(LED)

Show from

0000

Increase to

4000

The counting display function of.

1.74LS48

Is a seven-segment display decoder, and its pin diagram is as follows.

2-9

As shown in the figure. Now, the function of each pin is described.

Please wait a moment:

、

BCD

The input end of the code;

a、b、c、d、e、f、g

Is the output end;

draw

6 74LS48

Pin diagram

* * * Seven-segment cathode

Light Emitting Diode(LED)

Monitor is a commonly used display digital tube, but it should be noted that:

See clearly whether the digital tube you use is cathode or anode.

It is best to test it with a multimeter before use.

Polarity, pin diagram is as follows.

2- 10

As shown in, if it is a cathode, its pins

Computer output microfilm

Terminal grounding; If it is an anode,

Starting pin

Computer output microfilm

This segment should be connected to a high level.

Also pay attention to add a protective resistor to the digital tube circuit to limit the current.

draw

seven

* * * Seven-segment cathode

Light Emitting Diode(LED)

Display pin diagram

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