Design of automobile taillight control system based on Multisim

This paper designs a car taillight control design based on Multisim, which requires the taillight to be turned on and off when the car turns left, turns right, stops, etc. Multisim has the function of simulating various circuits by computer, and it can achieve the same functional effects as real devices by using various simulation devices.

Design requirements

Assume that there are three indicator lights on each side of the rear of the car (simulated by light-emitting diodes)

1. All indicator lights are off when the car is operating normally;

2. When turning left, the three indicator lights on the left will light up in a left-circular sequence;

3. When turning right, the three indicator lights on the right will light up in a right-circular sequence;

4. When braking temporarily, all indicator lights flash at the same time.

The design content includes using the master-slave JK trigger to form a 3-bit counter to provide pulses for the design of the left (right) cycle flashing control circuit of the car taillight; and using the 74LS138D 3-line-8-line decoder to control the on and off of the indicator light. Design a switch control circuit to control the flashing of the taillight and determine the working condition of the 74LS138D decoder.

Overall circuit diagram

1. Car taillight control circuit

Figure 1 Car taillight control block diagram

Figure 1 is a block diagram of the car taillight control circuit, in which the more complex parts are the ternary counting circuit and the decoding circuit. The switch control circuit is controlled by two switches, and the drive circuit is controlled by controlling the signal provided to the decoding circuit; the ternary counter circuit is composed of two master-slave JK flip-flops, and the characteristics of the master-slave JK flip-flops form a sequential logic circuit to realize ternary counting; the decoding circuit uses a 74LS138D decoder, and a 3-wire 8-wire decoder can control the output of 8 ports, but this experiment only needs to use 6 ports, and the remaining two ports are idle. The logical state of the 6 ports of the decoder is controlled by the ternary counter and the switch control circuit; the drive circuit uses a commonly used LED tube, which adopts a common anode form. The positive pole of the LED tube is connected to the +5V voltage, and the negative pole is controlled by the drive circuit to control the LED on and off.

2. Circuit structure and schematic diagram

(1) Switch control circuit (as shown in Figure 2)

Figure 2 Switch control circuit

One end of the switch is connected to a high level, and the other end is grounded (low level). 74LS86D is connected to the input control end of 74LS138. When the switches are closed or opened at the same time, the input is the same, and the output of 74LS86 is "0", then 74LS138 does not decode. If the two switches are opened at the same time, the output of 74LS04D is "1"; and 74LS10D is connected to a CP pulse, so the output of 74LS00D is completely determined by the CP pulse; when the two switches are closed at the same time, the output of 74LS00D is "1"; B switch is open; the analysis when B switch is closed and A switch is open is also implemented according to the above method.

(2) Ternary counter circuit (as shown in Figure 3)

Figure 3 Ternary counter circuit

The ternary counting circuit is composed of two master-slave JK flip-flops. The output Q1 of the first master-slave JK flip-flop is directly connected to the input of the 74LS138 decoder, and the output Q2 of the second master-slave JK flip-flop is also directly connected to the input of the 74LS138. At the same time, the other output of the second master-slave JK flip-flop is directly used as the J input of the first master-slave JK flip-flop. Note that Q2 should have a higher weight than Q1. In addition, the K inputs of the two master-slave JK flip-flops are both connected to a high level, so that the period of the changed pulse can be 3, thus realizing ternary counting.

(3) Decoding circuit (as shown in Figure 4)

Figure 4 Decoding circuit

The 74LS138 decoder is a commonly used 3-wire 8-wire decoder. As shown in the figure, terminals 4 and 5 are grounded, terminal 6 is connected to the control signal provided by the control circuit, and terminals 1, 2, and 3 are the output signals Q1 and Q2 of the first and second master-slave JK flip-flops, and the control signal of the control circuit. Since only 6 indicator lights are required, only 6 ports (left turn: Y0 Y1 Y2; right turn: Y4 Y5 Y6) are connected to the output end of the 74LS138 to control the signal lights. And, it is implemented according to the following truth table.

(4) Driving circuit: as shown in Figure 5

Figure 5 Driving circuit

Use LED to display the operation results. The positive end of the LED is connected to a 5V power supply. When the input to the right of the NOT gate is a high level, it becomes a low level after passing through the NOT gate, and the LED is on; when the input to the right of the NOT gate is a low level, it becomes a high level after passing through the NOT gate, and the LED is off.

3. Calculation and simulation process and results

Circuit operation results in each case:

○1 When switch A is closed and switch B is open (i.e. logic 10), the operating result is as shown in the figure:

Figure 6 A switch is closed, B switch is open.

○2 When switch A is open and switch B is closed (logic 01), the operating result is as shown in the figure:

Figure 7 A switch is open, B switch is closed operation result diagram

○3 The operating result when switches A and B are closed at the same time (i.e. logic 11) is as shown in the figure:

Figure 8 A and B switches are closed at the same time.

○4 When switches A and B are turned on at the same time (i.e. logic 00), the operating results are as follows:

Figure 9: Results of running with switches A and B turned on simultaneously

4. Components list

5. Design and Instructions

This design is simulated based on computer Multisim simulation software. The state conversion is realized through switches A and B. When A and B are closed at the same time, it is equivalent to the car braking, and the six indicator lights flash at the same time; when A and B are disconnected at the same time, it is equivalent to the normal operation of the car, and all the indicator lights are off; when A is closed and B is disconnected, it is equivalent to the car turning left, and the three indicator lights on the left flash in a left cycle; when A is disconnected and B is closed, it is equivalent to the car turning right, and the three indicator lights on the right flash in a right cycle. The "XFGI" frequency is more suitable to be 60HZ. Therefore, this design basically has the basic functions of commonly used car taillight control, realizes the functions of turning and braking indication, and has certain use value.

Design Summary

In this design, the more difficult part is to design the ternary counter circuit, and the control circuit and the connection between it and the decoder are more complicated. I think it is very clever to connect the switch A end with the decoder port C and discard the output Y3. There is also a small detail in the connection between the decoder and the drive circuit, that is, according to the requirements, the indicator light on the left should flash in a left cycle, that is, flash from D2 to D0 in sequence, so the decoder output ports Y0, Y1, and Y2 should be connected to the indicator lights D2, D1, and D0 in sequence.