In-vehicle anti-drunk driving safety system based on MSP430

Since May 1, 2011, the Criminal Law Amendment (VIII) and the revised Road Traffic Safety Law have been officially implemented, and drunk driving will be subject to criminal liability. With the actual implementation of the detention for dangerous driving for drunk driving, the media and all sectors of society have paid more attention to the issue of criminalizing drunk driving. Various countries have a wide variety of alcohol testing instruments, but because they are not installed inside the car, they can only be checked one-on-one by the traffic police holding the instruments, making the scope of drunk driving inspection narrow, and it is impossible to actively eliminate this dangerous driving behavior, and it is impossible to completely eliminate traffic accidents caused by drunk driving.

Therefore, we hope to design a vehicle-mounted anti-drunk driving safety system. The design of this vehicle-mounted anti-drunk driving control system is divided into two parts. The alcohol concentration detection and judgment part is installed near the steering wheel of the car to facilitate the driver's breath detection; the second part is the alcohol concentration excessive control ignition part. This part of the circuit is connected to the car igniter to control the ignition and alarm circuit. In this way, a full range of active prohibition of drunk driving can be achieved.

1 System Design

The working principle of this design is that when the driver starts the car, the indicator light will light up to remind the user that the device is started, and the driver must first exhale into the alcohol sensor. The gas is processed by the sensor, detection amplification and AD conversion, and then input to the main control

The chip makes a judgment. If the threshold voltage is exceeded, the buzzer sounds and the stepper motor cannot be started, which means that the car engine cannot ignite. At this time, the voice alarm circuit will start the alarm. On the contrary, if the alcohol content is not exceeded, the display prompts that the alcohol concentration is normal and the car can be started normally. Figure 1 shows the overall principle block diagram of the system.

2 Hardware Circuit Design

The core control module of the system is the MSP430F149 from TI of the United States. The highlights of this chip are low power consumption, rich on-chip peripheral modules, stable system operation, and compliance with modern environmental protection concepts. In particular, the chip comes with 10-bit and 12-bit ADC conversion, which is easy to use and fully meets the actual requirements of driving in real life.

1) Alcohol concentration collection

The alcohol concentration sensor MQK2 device is used at the input end of alcohol concentration collection. It uses a sensitive sintered body formed by sintered semiconductors. The manufacturing process ensures its long-term working stability; it has high sensitivity and good selectivity to ethanol vapor, high signal-to-noise ratio and low power consumption; these characteristics meet the needs of drivers' self-testing of drunk driving.

MQK2 is mainly composed of gas sensors and resistance wire. VH is connected to 5 V heating voltage, which can heat the resistance wire to 270-300℃; Vc is connected to the working voltage (range 5-24 V); the external voltage of this system is +5 V, and the sampling resistor RL = 2 kΩ. In this way, the resistance change of the MQK2 sensor can be converted into the change of the output voltage through the circuit in Figure 2, which can be converted into digital quantity through the A/D device inside the MSP430F149 for processing by the microcontroller.

Considering that alcohol concentration is converted from non-electrical quantity to electrical quantity by the sensor, the sensor outputs a voltage of 0 to 3.3 V and the voltage value is stable. Since the voltage range of the alcohol sensor output is 3 to 5 V, the output value of the alcohol sensor cannot be directly given to the microcontroller. It can be seen from the literature that the alcohol content is in a linear proportional relationship with the voltage signal generated by the alcohol sensor after detection, so a general proportional circuit can be selected to convert it to the voltage range of the microcontroller. In this design circuit, a sliding rheostat is used instead of an alcohol sensor, so the analog quantity input by the sensor can be directly sent to the microcontroller using the change of the sliding rheostat voltage input, thereby obtaining a one-to-one correspondence between alcohol concentration and voltage.

2) Motor drive and alarm module

When the alcohol content exceeds the limit, a buzzer and an 8550 transistor are used to drive the driver to remind him of drunk driving. The indicator light is a light-emitting diode connected to the microcontroller, and a 1-2 kΩ resistor is added to limit the current. When driving under the influence, the output port P6.7 of the microcontroller is set to 1, and the 8550 transistor amplifies the current of the microcontroller to drive the buzzer. When in normal use, the output port p5.0 is set to 1, and a current limiting resistor is added to prevent the diode from being burned out due to excessive current.

Here, a stepper motor is used to replace the ignition of a car in reality. The rotation of the stepper motor means that the car's engine starts, otherwise the car cannot start. Because the output current of the microcontroller cannot drive the motor, a driver module is needed to drive the motor. Based on theoretical analysis and actual conditions, a stepper motor and LN298 are selected as the hardware circuit.

To sum up, the system uses LCD12864 display module to provide a human-computer interaction interface, and the ADC conversion module performs analog-to-digital signal conversion; the data processing module is used to display the detection information on the 12864 screen, and it corresponds to the input analog quantity; the motor drive and alarm module is responsible for alarming the user when the input analog quantity is too high, and displaying relevant information about the alcohol content; or when the input analog quantity is not marked, it prompts the user to ignite normally.

3) Main components

Based on the above description of the hardware, the main components and their parameters used in this design are shown in Table 1.

3 Software Design

The main program flow chart of the system and the screenshot of successful compilation are shown in Figures 3 and 4. After the system is powered on, each module needs to be initialized and set to determine whether to issue a sound and light alarm, and at the same time send the calculated alcohol concentration value to LCD12864 for display. [page]

4 Physical debugging circuit

As shown in Figure 5, the entire circuit consists of two circuits: the hardware resources on the MSP430F149 system board (LCD12864 display, buzzer, light-emitting diodes, etc.) and a motor drive module circuit (LN298 drive module and DC motor).

When the microcontroller is powered on, the 12864 display shows welcome (as shown in the left picture of Figure 6). When the alcohol content is higher than the set value, the drunk driving information is displayed in Figure 6, and the motor is prohibited, which means that the ignition device of the generator is stopped. If the alcohol content is normal, it is prompted that the car can be driven safely (as shown in the right picture of Figure 6).

5 Conclusion

The system has designed the software and hardware circuits for the vehicle-mounted anti-drunk driving safety control system, and has conducted software and hardware joint debugging on the experimental circuit based on the 32-bit low-power main control chip MSP430 as the core chip, proving the feasibility and correctness of the designed circuit. The hardware circuit is simple and low-cost, and the modular software design is easy to debug, which has certain expansion and application value. However, the vehicle-mounted drunk driving prohibition system is closely related to human subjective initiative. How to intelligently identify whether the gas received by the alcohol sensor is exhaled by the person who is about to drive requires further research.