1. The title of the course design: four-person answering machine.

Two. Design tasks and requirements:

1. Design task

Design a question-and-answer answering device for four people to participate in the competition. When the countdown to answering questions is displayed by numbers, when counting from "9" to "0", there is no answer, and the buzzer rings continuously 1 second. When the player answers for the first time, the number of the player's team will be displayed, the buzzer will sound 1 sec, and the countdown will stop.

2. Design requirements

(1) The numbers of the four players are: 1, 2, 3 and 4. Each one has an answer button, and the number of the button corresponds to the player's number, which is also 1, 2, 3, 4.

(2) Set a control button for the host to control the system reset (turn off the light when the digital tube answers first) and start the answer first.

(3) The transponder has the functions of data latching and displaying. After the game starts, if a player presses the game button, the player's number will be locked immediately and displayed on the game display screen. At the same time, the speaker will give audio prompts, block the input coding circuit, and prohibit other players from participating in the competition. The number of the contestant who answers first will be kept until the host clears the system.

(4) The responder has the function of answering at a fixed time (9 seconds). When the host computer presses the start button, the timer starts to count down, and the timer display screen shows the countdown interval. If no one answers first, at the end of the countdown, the speaker will sound for 1 sec. The player's answer is valid within the set time (9 seconds), and the answer is successful. The speaker rings and the sound lasts 1 sec. At the same time, the timer stops counting down, the player number is displayed on the answer screen, and the remaining answer time is displayed on the timer screen until the host clears the system.

(5) If it's time to answer first, but no player answers first, the answer first will be invalid. The system speaker gives an alarm (sound lasts 1 sec), the input coding circuit is blocked, and the player is prohibited from answering overtime, and the time is displayed as 0.

(6) A quartz crystal oscillator or a 555 timer can be used to generate a pulse signal with the frequency of 1Hz as the CP signal of the timer counter.

3. Principle circuit and program design:

1. Overall block diagram of digital responder

As shown in figure 1 1 and 1, it is a general block diagram. Its working principle is as follows: after the power supply is turned on, the host switches the switch to the "reset" state, the responder is in the forbidden state, the digital indicator light is turned off, and the timer displays the set time; The host turned the switch to the "start" state and announced that the answering machine was "started". The timer began to count down. When the player tries to answer questions within a fixed time, the responder completes: priority judgment, number locking and number display. After one round of answer, the timer stops, and the second answer is prohibited, and the timer shows zero. If you answer first, the host must operate the "Clear" and "Start" status switches again.

Figure 1 1, 1 block diagram of digital responder

2. Unit circuit design (1) transponder circuit

The reference circuit is shown in figure 1 1 and 2. The circuit has two functions: first, it can distinguish the order of the player's keys, and latch the number of the priority responder, while decoding the number displayed by the display circuit; Second, other players are forbidden to press keys. Working process: When the switch S is set to the "clear" terminal, the terminals of the RS flip-flop are all 0, and the outputs of the four flip-flops are all set to 0, so that 74LS 148 = 0, which makes it work. When the switch S is set to "Start", the transponder is in a waiting state. When a player presses a key (such as S4), after the output of 74LS 148 is latched by RS, 1Q= 1, 74LS48 is in working state, and 4Q3Q2Q= 100. In addition, 1q = 1 disables 74LS 148 = 1+0, and prevents other keys from being input. Release and press this key, and 74LS 148 is still 1q = 1, so that ST = 1. Therefore, 74LS 148 is still in the forbidden state, which ensures that no signal will be input when the key is pressed twice, and ensures the priority of the responder. If there is a rush to answer again, the host needs to reset the S switch and clear it before the next round of rush to answer. 74LS 148 is an 8-line -3-line priority encoder.

Figure 1 1.2 digital transponder circuit

(2) Timing circuit

Figure 1 1.3 Timing circuit with preset time

The host first sets the time for answering, the counter is preset by the preset time circuit, and the clock pulse of the counter is provided by the second pulse circuit. The preset time circuit is designed with decimal synchronous up-down counter 74LS 192. The specific circuit is shown in figure 1 1 and 3.

(3) Alarm circuit

(4) Zero latch circuit

(5) Time sequence control circuit

Timing control circuit is the key to the design of responder, and it has to complete the following three functions:

(1) When the host puts the control switch in the "start" position, the emergency response circuit and the timing circuit enter the normal emergency response working state.

(2) When the player presses the answer key, the answer circuit and the timing circuit stop working and the countdown returns to zero.

(3) When the set answering time is up and no one answers, the answering circuit and the timing circuit stop working.

Second pulse waveform

Four. Component selection

1. integrated circuit: 74l148174l373174l48274l1921ne555174l002.

74LS 12 1 2 tablets 74LS2 1 1 tablets 74LS32 1 tablets 74LS08 1 tablets.

2. Resistance |: 100Kω 2 only 40ω 2 only 15Kω l only 68Kω l only.

3. Capacitance: 10UF 3 pieces 10nf 1 piece.

4. Others: 2 cathode displays, 1 double-pole single switch, 4 PBNO switches and 2 buzzers.

Fifth, the overall circuit and software simulation renderings and simulation debugging results analysis.

555-second pulse diagram

Working principle of intransitive verbs

1. digital setting: set the load input of 74ls 192 to a high level through the single-pole double-throw switch, so that 74ls 192 can realize the digital setting function and set it to 100 1. Then set the load input to a low level through the switch and start the countdown.

2. When the host presses the start button, the buzzer sounds, and the player starts to answer the questions first, and the countdown begins. When any player presses the button, LS 148 is locked, the buzzer sounds, and other players press it. At the same time, the countdown stops, and the digital tube displays the remaining time and the number corresponding to the player. The countdown digital tube shows 0, and the buzzer sounds, so it is forbidden for players to answer first. The host will set it to the start state again, other players can continue to compete for answers, and the countdown will count down to the next competition state.

3. When no player presses the "Yes" button, the countdown will continue until it is zero. At this time, the signal from zero will latch LS 148, and it will be invalid for the player to press the button again. Similarly, other players can only continue to answer first if the host clears it and then sets it to the starting state.

4. Realization of latch: When the signal of LS373 is input, the signal is fed back to the enabling terminal EI of LS373 through 74LS2 1. At this time, LS 373 is locked in a high position, and other players are prohibited from rushing to answer. At the same time, a low-level signal is fed back to the countdown input terminal of LS 192, and the work is stopped to maintain the remaining strokes. When the countdown is 0, the signal is fed back to the enable terminal EI of 74LS32 through 74LS 148. At this time, LS 148 is locked at a low level and stops working, and no player is allowed to answer overtime. At the same time, the low-level signal is fed back to the countdown input terminal of 74ls 192 to stop working and countdown. The host computer controls the enabling terminals of LS373 and LS 148 to clear the latch signal through the single-pole double-throw switch, so that the transponder can work again.

Seven. abstract

1. Through this course design, I have strengthened my ability to do things, think and solve problems.

During the whole design process, I have been thinking about two schemes, and the other scheme took two days. Both the schematic diagram and the simulation diagram have achieved the results, but the physical results always fail to meet the requirements of the topic. So I spent another day making this scheme, which is simpler than the other scheme, including the circuit principle and connection, and the selection of the chip.

2. In the design process, we often encounter such a situation, that is, we always think that this connection can work, but we always can't connect the circuit. So whether eating or sleeping these days, my mind is always thinking about how to solve these problems and how to come up with a better connection method. But strangely, thinking about these problems all day long will not make you feel tired at all. Perhaps it is curiosity that drives fatigue out of the clouds!

3. I am so immersed in the curriculum design, which also consolidates and strengthens the textbook knowledge. When reading textbooks at ordinary times, sometimes I can't understand the problem. When I finish the course design, those problems will be solved. You can remember many things. For example, some chips read textbooks at work. I saw it this time, but I will forget it next time, mainly because I haven't practiced it! Knowledge comes from practice, which is the driving force and ultimate goal of knowledge, and practice is the only criterion for testing truth. Therefore, a small curriculum design has such a great effect on us.

After several weeks of hard work, with the help of teachers and classmates, I have basically completed the design task. Through this course design, I fully realized the importance of self-study and the truth of applying what I have learned, and I also realized a lot of fun in completing one thing by myself and successfully solving difficulties. I looked up a lot of information in the library and online, and I also realized the important role of the library and online search. In the future study process, you should go to the library and read professional books online to enrich your knowledge. It also deepened my understanding and application of digital circuit technology. Due to the limitation of knowledge level, there may be some shortcomings in the design. Sincerely accept the criticism and correction of teachers and classmates.

Finally, I sincerely thank the teachers for their careful guidance and the students for their enthusiastic help!