Design of buzzer-beater based on 74LSll2JK trigger

Abstract: Based on the characteristics of the JK flip-flop that its state changes only once during each clock pulse action time, and different pins can change the state of the flip-flop, the design method and simulation of the buzzer-answering machine using the JK flip-flop are given, and the optimal design method and ideas of the buzzer-answering machine using the 74LSll2JK flip-flop are also given.
Keywords: JK flip-flop; buzzer-answering machine; clearing; shielding

O Introduction
Answer machine is an instrument that uses triggers to realize the host switch reset, the answerer's answer, and the shielding of those who failed to answer. It displays and indicates the first answerer through the answerer's indicator light. Therefore, it can be widely used in various intelligence answering competitions. This article takes the design of a three-person answerer with a 74LSll2 trigger as an example and gives its design method.

1 Design requirements
According to the on-site use of general buzzers, this buzzer should meet the following requirements:
(1) A host switch and a three-person buzzer switch should be designed;
(2) When the host switch is pressed, the personal indicator light goes out and the blockade of the answerer is released. This requires that the host switch in the circuit can restore the circuit to its initial state;
(3) When the personal switch is pressed, the indicator light of the individual turns on and the answer of others is blocked at the same time; this requires the circuit to have memory and shielding functions.
The 74LSll2 used in this design is a double falling edge JK trigger, and its function table is listed in Table 1.

2 Design Scheme
There are many schemes for the design of the buzzer. The following are the design circuits of several schemes:
The first scheme is to use zero reset, and the starting end of the buzzer responder is connected to GND. When the person who successfully answers presses the switch before others, J changes from 0 to 1, Q changes to high level, and changes to low level, and blocks the buzzer response switches of others through the NAND gate. The circuit is shown in Figure 1.

The second solution is to use the terminal to set the trigger to 1 and effectively clear it to zero, and the indicator light is connected to the terminal. Before answering, the answer switch is connected to a high level. The person who successfully answers the question takes the switch before others, and it will be connected to a low level. The K terminal changes from 0 to 1, and the corresponding indicator light becomes bright, while shielding other answerers. The circuit is shown in Figure 2.

The third solution is to use the terminal clearing. Before answering, the answerer's switch is grounded. The answerer who succeeds will connect the switch to a high level and provide a falling edge to the JK trigger. When J and K are both 1, the trigger state flips, the indicator light turns on, and the switches of other answerers are shielded. The circuit is shown in Figure 3.

The reset principle of the fourth scheme is the same as the above schemes. Before answering, the answerer's switch is grounded, and the answerer who successfully answers connects the switch to a high level before others, and then the indicator light turns on. The principle circuit of this scheme is shown in Figure 4.

The fifth scheme is to use the trigger to set to 1 and clear to zero, and the respondent uses the response. The response principle will not be described in detail. The circuit is shown in Figure 5.

In the above scheme, 74LS74 is a dual D flip-flop. As long as the J and K terminals of 74LSll2 are connected to a high level at the same time, a simple buzzer can be designed using schemes three, four, and five of the above five schemes.

3 Design method
As long as you understand the principle of the trigger, you can use the trigger to design an intellectual answering machine, so as to realize the desired function step by step.
3.1 Implementation of the reset function
The key to realizing the reset function is the design of the host switch. There are two ports in the JK trigger that are not controlled by Cp and can directly control the output (i.e., terminal A and terminal B). Considering that the host switch is generally from the indicator light to the indicator light off, the indicator light should be connected to different output terminals (Q and terminal A) for different reset methods. If reset is used, the indicator light should be connected to Q, otherwise, the indicator light switch should be connected to terminal A, and the unused terminal A should be connected to a high level. However, it should be noted that A and B cannot be 0 at the same time, otherwise, the switch should use a self-resetting switch.
3.2 Implementation of the answer function
The indicator light of the JK trigger can be controlled by five ports, A, B, Cp, J, and K, respectively, to control the output indicator light on and off. Therefore, five methods can be used to realize the answer function, but it must be considered that the terminal A and B cannot be 1 at the same time. In addition, different methods also have different Cp input frequency requirements.
3.3 Shielding of failed answers
To achieve the function of shielding those who failed to answer, there are four logic circuits that can be used: AND gate, OR gate, NAND gate, and NOR gate. After selecting the gate circuit, you can choose to connect the input end corresponding to different gate circuits. The method (taking the NAND gate as an example) is: the NAND gate requires that the output is 0 when all inputs are 1, so the output end that starts with 1 should be connected to the input end of the NAND gate, and then determine whether the starting switch is connected from a high level to a low level or from a low level to a high level. In general, in order to prevent the outside world from affecting the overall circuit, the switch is usually connected from a low level to a high level when answering. Finally, reverse the selection to connect the JK output end of the gate circuit to see if it meets the requirements. The advantages and disadvantages of the various schemes described in this article are compared in Table 2.

Therefore, considering all factors, it can be determined that option three is the best option.

4 Conclusion
There are 2 solutions for the JK flip-flop to control the clear port, 5 solutions for the quick-answer function, and 4 solutions for the switch to shield others. They have their own advantages and disadvantages. As long as you understand
the principle of the JK flip-flop, you can design a quick-answer solution based on the function to be realized. Finally, consider the advantages and disadvantages of each solution and design the best solution. In addition, since the D flip-flop can be realized by connecting the JK flip-flops together, the solutions 3, 4, and 5 introduced in this article are also applicable to the D flip-flop.