Overall block diagram: Because the three indicator lights light up circularly when the car turns left or right, the ternary counter is used to control the decoding circuit to output low levels in turn, thus controlling the taillights to light up as required. From this, the relationship between each indicator lamp and each given condition (S 1, S0, CP, Q 1, Q0) is obtained, that is, the logical function table (as shown in Table 6-2 (0 in the table indicates that the lamp is off, and 1 indicates that the lamp is on).
The overall block diagram of table 1 is as shown in the figure.
Figure 1 Principle block diagram of automobile taillight control circuit
Table 1 automobile taillight control logic menu
on-off control
S 1 S0
Ternary counter
Q 1 Q0
Six indicator lights
D6 D5 D4 D 1 D2 D3
0 0
0 0 0 0 0 0
0 1
0 0
0 1
1 0
0 0 0 1 0 0
0 0 0 0 1 0
0 0 0 0 0 1
1 0
0 0
0 1
1 0
0 0 1 0 0 0
0 1 0 0 0 0
1 0 0 0 0 0
1 1
CP CP CP CP CP CP
3.2 Unit Circuit Design and Analysis
3.2. 1 Design of Switch Control Circuit
Let the enabling signals of 74LSl38 and display driving circuit be G and A respectively, and according to the analysis and combination of the whole logic function table, the truth table and given conditions (S 1, S0, CP) of G and A are obtained, as shown in Table 2.
on-off control
S 1 S0
cerebral palsy
Enable signal
General Motors Corporation
0 0
0 1
0 1
1 1
1 0
1 1
1 1
cerebral palsy
0 CP
The truth table of table 2s 1, S0, CP and g, a logic function.
Logical expressions sorted by Table 6-3
, ,
The switch control circuit based on the above formula is shown in Figure 2.
Fig. 2 Switch control circuit
3.2.2 Design of ternary counter circuit
According to the table 1, a ternary counter circuit can be constructed with double J-K flip-flops 74LS76. The circuit is simple in structure and low in cost, so this scheme is selected. The circuit diagram is shown in Figure 3.
Figure 3 ternary counter
3.2.3 Design of Decoding and Display Driving Circuit
The function of the decoding and display drive circuit is to provide six taillight control signals under the output of the switch control circuit and the status of the ternary counter. When the control signal output by the decoding driving circuit is low level, the corresponding indicator lamp lights up. Therefore, the decoding and display driving circuit can be composed of 74LS 138 (see table 3.3 for the function list), six NAND gates and six inverters, and the logic circuit is shown in figure 3. 10 (i). In the figure, the input terminals c, b and a of the decoder 74LS 138 are connected to K 1, Q 1 and Q0, respectively. When G=F= 1 and K 1=0 in the figure, the decoder output is 0 in turn for counter states Q 1Q0, 0 1 0, so that indicator lamps d 1, D2 and D3 correspond. When G=F= 1 and K 1= 1 in the figure, the decoder outputs are 0 in turn for the counter states Q 1Q0, 0 1 0, so that the indicator lights D4, D5 and d 6 correspond. When G=0 and F= 1 in the figure, all the decoder outputs are 1, so that all the inverter outputs corresponding to all the indicator lights are at high level, and all the indicator lights are turned off; When G=0 and F=cp in the figure, all indicator lights flash at the frequency of cp. Four different modes of taillight status display are realized.
3.3.4 Design of Taillight Circuit
The taillight display drive circuit consists of six light-emitting diodes and six resistors. The output of the inverter G 1-G3 is also 0 in turn, and the indicator light D 1→D2→D3 lights up in turn, indicating that the car is turning right. The output terminals of inverters G4 ~ G6 are 0 in turn, so the indicator lights D4→D5→D6 light up in turn, indicating the car to turn left. When G = 0 and A= 1, the output terminals of 74LSl38 are all 1, and the output terminals of G6 ~ G 1 are all 1, and the indicator lights are all off; When G = 0 and A = CP, the indicator light flashes at the frequency of CP.
3.3.5 second pulse circuit design
A multivibrator consisting of 555 timers; As shown in Figure 4, the circuit of multivibrator has large output driving current and flexible function due to the sensitivity of the internal comparator of 555 timer, and the influence of voltage and temperature on frequency is small. That is, the oscillation frequency of the multivibrator is stable.
Fig. 4 Pulse generating circuit
3.3 Installation and debugging of the circuit
Its working principle diagram is shown in Figure 5. After the analysis of the above design contents and requirements, the circuit schematic diagram of the automobile taillight controller can be shown in Figure 5.
Fig. 5 Circuit schematic diagram
Firstly, a multivibrator with a 555 timer generates a pulse signal with a frequency of 1Hz as the input signal of a ternary counter with a double J-K flip-flop and a three-input NAND gate in the switch control circuit.
Secondly, a ternary counter composed of double J-K flip-flops generates cyclic signals of 00, 0 1, 10, providing the original signals of turning left and right.
Finally, the high and low potential signals provided by 6 NAND gates, 6 NOT gates and 74 10 are respectively output to the left and right taillights. The obtained signal can be output to LED to realize the required function.
4 experiences and suggestions (Article 4, bold type)
4. 1 Experience (Song typeface small four, bold)
This course design is my biggest gain at present. I am an engineering major, and design is our necessary skill in the future. This course design just provides us with an opportunity to apply what we have learned, from looking for information in the library to designing and simulating the circuit, and finally forming the circuit. It can be said that this course design is bittersweet. The design concept is the most important. As long as your design idea is successful, your design is half successful. Therefore, we should make full preparations before the design, such as searching for detailed information, so as to lay a solid foundation for the success of our design. The production process is a process of testing people's patience. We should not be impatient or careless. Circuit debugging should be gradual, not impatient, because debugging on the computer is slow, requiring a more correct debugging method, such as fast frequency modulation. This requires us to be flexible and can speed up the progress without affecting the experiment. It is necessary to master the knowledge in the textbook so as to analyze and solve the problems in the experiment. What impresses me most is that to design a successful circuit, you must have patience and perseverance. In the whole circuit design process, the most time-consuming is the connection of each unit circuit and the detailed design of the circuit, such as the supply of CP pulse. In the choice of various schemes, we carefully compare and analyze their principles and feasible reasons. Finally, under the patient guidance of the teacher, the whole circuit can work stably. In the design process, I deeply realized that in the design process, it is necessary to practice repeatedly, and the process is likely to be quite cumbersome. Sometimes circuits that take a long time to design still need to be redone. At that time, I was a little discouraged and sometimes I really wanted to give up. At this time, it is even more necessary to calm down and find out the reason. Generally speaking, this internship has benefited me a lot. In the process of exploring how to design the circuit to realize the required functions, it is particularly interesting, which cultivates my design thinking and increases my practical operation ability. While making me realize the hardships of designing circuits, I also realize the joy and happiness of success.
4.2 Suggestions
For students, it is better to do curriculum design or finish it independently. Be sure to understand the characteristics and attributes of each component before design, so that you can sit in the right position when designing. And when designing, you should understand "what do you want and how to do it" so as not to be blind. For all the errors that will occur in the design, we must carefully check the circuit, and don't blindly think that the components are faulty or other man-made problems. The most important thing in curriculum design is to exercise practical ability, so we should pay attention to thinking independently about how to design, rather than copying.
For instructors, whether they can arrange experiments in sufficient time, or choose topics, don't limit the topics too dead, and fully stimulate students' interests and hobbies, so as to do curriculum design more passionately and profoundly.
5 Appendix
Component list
Component name
standard
amount
electric resistance
100Ω
500Ω
eight
2
electric capacity
100μF/25V
2
Light Emitting Diode(LED)
Light-emitting diode (negative)
six
555 timer
NE555
1
translator
74LS 138
1
change
2
Other drama series
ingredient
74LS00
74LS04
74LS 10
74LS76
74LS86
1
1
1
1
1
6 references