abstract

This paper introduces a multifunctional digital display responder composed of digital circuits, which mainly adopts 74 series commonly used integrated circuits. In addition to the basic answering function, it also has the functions of timing alarm and digital display. When you start answering questions, the system will automatically count down and the time can be preset. If someone answers, the system will stop timing. If there is no answer, the system will send out a short alarm to remind you that the answer is over.

key word

Single chip microcomputer, PLC, emergency response, alarm and digital display

First, the design purpose

On TV and in school, we often see some intelligence programs that scramble to answer questions. If the responder is asked to raise his hand, the host will easily misjudge, which will lead to unfair response. In order to judge the first responder accurately, fairly and intuitively in the competition, the designed responder usually indicates the first responder by means of digital display, lighting and sound. In order to prevent this unfairness, only the high accuracy of electronic products can ensure the fairness of the first answer.

Second, the procedure.

There are many ways to make the responder, which can be completed by single chip microcomputer. Powerful function, simple manufacture and few peripheral components. It can also be realized by PLC, and the production is relatively simple; It can also be made by EDA technology we have learned; Finally, it can also be realized by digital circuits. Its principle is relatively simple, and the integrated block is relatively cheap and easy to buy. It is closely related to the "digital circuit" we have learned, and it is of great significance to consolidate what we have learned. NE555 standard second pulse circuit and other forming circuits are adopted, which makes the whole scheme easy to realize.

Scheme 1

1 principle block diagram

The overall block diagram of the timer is shown in figure 1, which consists of main circuit and expansion circuit. The main circuit completes the basic answering function, that is, when the player presses the answer key, it can display the player's number, and at the same time, it can block the input circuit and prohibit other players from answering. The expansion circuit completes the function of answering in time.

Figure 1

The working process of the timer responder shown in figure 1 is as follows: when the power is turned on, the host puts the switch in the "reset" position, the responder is in the forbidden working state, the digital display is turned off, and the timer displays the set time. When the host announces "start answering" and turns the control switch to the "start" position, the speaker gives a sound prompt, the answering machine is in working state and the timer counts down. When the time is up, but no player answers first, the system will call the police, block the input circuit, and prohibit the player from answering first after overtime. When the player presses the answer key within a fixed time, the receiver should complete the following four tasks:

(1) The priority coding circuit immediately identifies the number of the respondent, which is latched by the latch and then displayed by the decoding display circuit;

(2) The speaker makes a short sound to remind the program host to pay attention;

③ The control circuit should block the input coding circuit to prevent other players from rushing to answer again;

(4) The control circuit should stop the timer, and the time display shows the remaining time for answering questions until the moderator clears the system. When the player finishes answering the questions, the host operates the control switch to make the system return to the forbidden working state, so as to carry out the next round of competitive answering.

Option 2

1 principle block diagram

The function completed by this circuit is shown in Figure 2. When the host announces the start of the game, press the start button, and the circuit will enter the game state. The input of the player adopts scanning input, and then the corresponding information is sent to the single chip microcomputer, and then the single chip microcomputer outputs it to the display output circuit. At this time, someone presses the corresponding answer key for the first time. After the control and selection of the single chip microcomputer, the corresponding number is displayed on the eight-segment display and latched, and the input of other keys is prohibited.

(Figure 2)

Option 3

1 principle block diagram

The function of this circuit is shown in Figure 3. After the host turns on the start switch, if a group presses the first answer button within the set time to, it will drive the sound effect circuit ① to make a sound, and the indicator light LI will be on, and the first successful answer group number will be displayed on the 8-segment nixie tube display. At this time, the circuit will interlock, and it will be invalid for other groups to press the first answer key.

If there is no answer within the time TO, the sound effect circuit ② is driven to sound, and the indicator light L2 is on, indicating that all respondents give up asking questions;

After the answer is successful, the host turns on the time limit switch SW2 and starts the timer, and the answer is valid within the set time ti. When the set time ti is reached, the sound circuit ③ is driven, and the indicator lamp L3 is lit, indicating that the answering time is up.

(Figure 3)

Third, the scheme selection

Scheme comparison

digital circuit

single chip microcomputer

Programmable Logic Controller (PLC)

Production difficulty

low

ordinary

ordinary

Realization difficulty

ordinary

low

low

price

low

ordinary

high

Circuit principle

simple

ordinary

ordinary

Design difficulty

simple

high

ordinary

Through the comparison of the above schemes, the making scheme of digital circuit is relatively easy to realize and the principle is simple, so I choose the first scheme to complete the responder circuit.

Fourth, design the system function.

1. Basic functions:

(1) is for 8 players to play at the same time, and is represented by 8 buttons S0 ~ S7 respectively.

(2) Set the system sorting and response control switch S, which is controlled by the host.

(3) The transponder has the functions of locking and displaying. That is, the player presses the button to latch the corresponding number, the speaker gives a sound prompt, and the number of the player is displayed on the seven-segment digital tube. Priority is locked for the player who answers first, and the number of players who answer first remains until the host clears the system.

2. Extended functions:

(1) The answering machine has the function of answering at regular intervals, and the time for answering at a time is set by the host (for example, 30 seconds). When the host starts the "Start" key, the timer starts to count down.

(2) The contestants should answer first within the specified time. If the answer is valid, the timer will stop working, and the number and time of the contestants will be displayed on the display screen until the host clears the system. (3) During this period, if the scheduled time has come and no one answers first, the system will call the police and prohibit the scheduled answer, and 00 will be displayed on the scheduled display screen.

Five, the design of each part of the unit circuit

Main circuit design of (1) transponder

The answering circuit has two functions: first, it can distinguish the order of the player's keys and latch the number of the priority responder for the decoding display circuit; The second is to invalidate the key operation of other players. Priority encoder 74 148 and DFF latch can complete the above functions, and their circuit composition is shown in Figure 4. Its working principle is that when the host control switch is in the "reset" position, the terminal of the RS trigger is low, and the output terminals (4Q~ 1Q) are all low. So 74LS48 =0, the display is off; 74 148 =0 gate input, 74LS 148 is in working state, and the latch circuit does not work at this time. When the host switch is turned to the "start" position, the priority coding circuit and the latch circuit are in working state at the same time, that is, the transponder is in waiting working state, waiting for the input signal from the input terminal 7 ... 0. When a player presses the key (such as S5), the output of 74LSl48 is =0 10, =0, and after passing through the RS latch, CTR=l,. When the pressed key is released, the 74LSl48 is at the high level, but because CTR remains at the high level, the 74LSl48 is still in the disabled state and will not receive input signals from other keys. This ensures the priority of the responder and the accuracy of the responder circuit. When the priority responder finishes answering the question, the host operates the control switch S to reset the responder circuit for the next round of responder.

(Figure 4)

74LS 148 is an 8-line -3-line priority encoder, and the table 1 is its menu.

Function truth table of table 1 74LS 148

(2) Design of timing circuit

Principle and design: This part mainly consists of 555 timer second pulse generating circuit, decimal synchronous up-down counter 74LS 192 subtraction counting circuit, 74LS48 decoding circuit and two 7-segment digital tubes, that is, related circuits. The specific circuit is shown in Figure 5. The two modules 74LS 192 realize subtraction counting, which is displayed on the digital tube through the decoding circuit 74LS48, and its clock signal is provided by the clock generation circuit. 74 192 preset number control terminal realizes preset number. According to the difficulty of answering questions, the program host sets a time for answering questions, and preset a counter through a preset time circuit. If you want to set it to 30S, you can enter 00 1 10000 at the preset number control terminal of the counter. The clock pulse is provided by the second pulse circuit. After the button pops up, the counter starts to count down and displays the time on the cathode seven-segment digital tube. When someone answers first, it stops counting and shows the countdown time. If no one answers first, the countdown time is up, and the low level is output to the timing control circuit to control the alarm circuit to alarm. At the same time, the player's first answer is invalid in the future. The specific circuit is shown in Figure 5.

(Figure 5)

Second pulse generating circuit: The second pulse is provided by NE555, and the pulse frequency output from its terminal 3 is

, combined with our practical experience, considering the cost of components, we choose resistance values R 1= 15K, R2=68K, C= 10uF and substitute them into the above formula, that is, second pulse.

(3) Design of alarm circuit

The alarm circuit composed of 555 timer and triode is shown in Figure 6. Where 555 constitutes a multivibrator with oscillation frequency.

Its output signal pushes the loudspeaker through the triode. PR is the control signal. When PR is high, the multivibrator works, and when PR is low, the circuit stops oscillating.

(Figure 6)

(4) Design of timing control circuit.

The AND gate G 1 is used to control the release and inhibition of the clock signal CP, and the gate G2 is used to control the input enable terminals of 74LS 148 (that is, the five terminals in Figure 2). The working principle of fig. 7 is that when the host control switch is switched from the "reset" position to the "start" position, the output of 74LS279 in fig. 2 is 1Q, that is, CTR=0, and the output after G3 inversion is 1, then the clock signal CP generated by NE555 can be added to the CP of 74LS 192. At the same time, when the timing time is not up, the "timing to signal" is 1, and the output of gate G2 is 0, so that 74LS 148 is in a normal working state. When the player presses the answer key within a fixed time, CTR = 1 is inverted by G3, and the output is 0, blocking the CP signal and keeping the timer working; At the same time, the output of gate G2 = 1, 74LS 148, is in a prohibited operation state. When the timed time is up, the "timed arrival signal" is 0, /ST= 1, 74LS 148 are in a prohibited working state, and players are prohibited from rushing to answer. At the same time, the gate G 1 is in the closed state, blocking the clock CP signal and keeping the timing circuit in the 00 state unchanged, and this scrambling is over.

(Figure 7)

The integrated monostable trigger 74LS 12 1 is used to control the alarm circuit and sound time (see Table 2 for its function table). The specific principle is as follows: it mainly consists of a 555 clock circuit (used to control the alarm audio frequency), a buzzer, a related delay circuit and a control circuit. The monostable trigger 74 12 1 controls whether or not to alarm and the alarm time through signals /Ys, BO2 and s, and the 555 clock circuit generates a pulse clock. When someone answers first at the specified time, /Ys jumps from 1 to 0,74121,and the state is 2, that is, Q outputs a transient high level, and the buzzer continuously gives an alarm sound =2. 15 seconds; If there is no answer within the specified time, BO2 will jump from 1 to 0,74 1 21,and the state of1will appear. Q will output an instantaneous high level, and the buzzer will sound continuously for an alarm duration of.

Combined with the alarm circuit shown in Figure 6, the analysis and calculation are as follows. Let c = C= 100uF, R=25K = 25k. Yes = 2. 15 seconds. (See Figure 8 for schematic diagram)

(Figure 8)

Table 2 74 12 1 menu

(6) Power supply circuit

The power supply circuit adopts three-terminal integrated linear voltage-stabilizing integrated block L7805CV, because its peripheral circuit is relatively simple and stable, which is very suitable for 74 series integrated blocks. Its voltage stabilization accuracy is 2%, its working current is 1.5A, its package is TO-220(A), its working temperature is also very good, and it has over-temperature protection and short-circuit protection, and its maximum input voltage is 35V, which can greatly guarantee the long-term operation of the circuit. (See Figure 9 for the specific circuit)

(Figure 9)

Abstract of intransitive verbs

Graduation design is not only a test of previous knowledge, but also an improvement of one's own ability. Let me briefly summarize the whole graduation design process.

First, choose a topic after receiving the task. Choosing a topic is the beginning of graduation design. Choosing a suitable and interesting topic has a great relationship with whether the whole graduation project can be carried out smoothly. Just like walking, the first step is decisive, and the direction of the first step needs careful consideration. Otherwise, you may take many detours, take many twists and turns, or even do the opposite, making it difficult to reach your destination. Therefore, choose; Be sure to think about the problem.

Second, after the topic is determined, it is to find information. Searching for information is the preparation for graduation design, and a good beginning is half the battle. Although going to the library, bookstore and reference room is a primitive way, it also has some merits. In a word, no matter which way you check the information, it is valuable, so you should record it one by one for future use.

Thirdly, through the above process, we have accumulated a lot of information and probably have some understanding of the topic. This step is to make a more thorough analysis of the topic based on the existing information.

Fourth, with the research direction, it should be realized. In fact, the first three steps are all paving the way for this step.

Through this design, I have a certain understanding of the logical relationship in digital circuit design, a certain new understanding of the digital circuit I have learned before, and a review of the knowledge I have learned before, as people often say, but I have encountered many problems in the design process, and some knowledge is not clear, but I have reviewed the content of the digital circuit again through some materials. In this graduation project, the relationship between our classmates has been further improved. Students help each other. If there is anything we don't understand, we can discuss it together, listen to different opinions and better understand our knowledge. So I am very grateful to my classmates who have helped me here.

Thank my tutor and teacher for giving me such an opportunity to exercise. In the whole process of graduation design, I learned a lot, and also cultivated my ability to work independently, and established my confidence in my work ability, which I believe will have a very important impact on my future study, work and life. But also greatly improved the practical ability, so that I fully realized the difficulty of exploration and the joy of success in the creative process. Although this project is not perfect, what I learned in the design process is the biggest harvest and wealth of this graduation design, which will benefit me for life.