Talking about the Design Scheme of Vehicle Alcohol Detection Controller Based on MSP430

This paper proposes an ultra-low-power alcohol detection controller based on MSP430 microcontroller. The instrument is installed in the car. When the driver enters the cab, the alcohol concentration can be detected automatically to ensure the safety of driving. The system can control whether the car igniter is turned on or off according to whether the detected alcohol content exceeds the standard. If the standard exceeds the standard, the driver cannot start the car, thus fundamentally eliminating the appearance of drunk driving. The system has the advantages of high cost performance, high intelligence and stable and reliable operation.

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How the system works

The system uses ultra-high sensitivity alcohol sensor, ultra-low power single-chip system, and automatically detects the alcohol concentration method, which can prevent the driver from evading detection to judge whether the driver is drunk driving. The overall design of the system is shown in Figure 1. The system can be placed in the dashboard of the car. When the driver starts the car, the detection controller starts, and the engine is locked and the car cannot be started. After the alcohol sensor is heated, the detection controller detects the gas signal detected by the alcohol sensor.

Since the alcohol content is in a specific proportional relationship with the voltage signal generated after the detection of the alcohol sensor, the alcohol content can be judged based on the voltage signal. After the detected signal is amplified and filtered, it is converted into a digital signal by a built-in 12-bit ADC of the microcontroller, and the signal is processed by the single-chip microcomputer. It is assumed that the alcohol content is not exceeded, the LCD display screen displays the current alcohol concentration, and the normal indicator lights up. The control relay does not work and the car starts up;

On the contrary, the sound and light alarm is given, the control relay cuts off the power of the ignition device, and the driver cannot start the car, thereby fundamentally controlling the drunk driving. After the car is started, the controller enters a low-power state. Only the alcohol concentration detection circuit works all the time. Once the driver is drinking during driving, the controller immediately returns to normal operation.

Figure 1 System overall structure

System hardware design

1 main control circuit design

This controller uses the MSP430FG4619 from the 16-bit ultra-low-power, high-performance MSP430 microcontroller series from Texas Instruments. It is only 350μA in active mode, and the leakage current of the line input is 50nA maximum; its high integration not only greatly reduces the failure rate, but also has obvious advantages in terms of cost, volume and stability.

The MSP430FG4619 in the Alcohol Detection Controller system is used to determine the alcohol content in the gas and control the operation of the entire control unit. The system main control circuit is shown in Figure 2, including the crystal oscillator circuit, reset circuit and JTAG interface circuit.

Figure 2 Schematic diagram of the system main control circuit

2 alcohol detection circuit

The alcohol detection circuit consists of a high-precision alcohol sensor, a signal conditioning amplifier circuit, a filter circuit, and a built-in 12-bit ADC of the microcontroller, as shown in Figure 3. The main function is to detect the alcohol content and determine if it exceeds the standard.

Figure 3 Alcohol detection circuit diagram

The alcohol sensor adopts the bypass heat type semiconductor alcohol gas sensor MQ3, which has high sensitivity and good selectivity to ethanol vapor, rapid response recovery, long-term life and reliable stability, and the detection range is 10 to 1000 ppm. Especially suitable for the detection of drunk drivers.

The front stage of the signal conditioning amplifier circuit is realized by the high-precision op amp MAX4238 produced by Maxim. It has a bias current of 1pA, a bias voltage of 2μV, ultra-low temperature drift, and good performance. The post-stage amplification is realized by the commonly used OP07C operation amplification. The filter chip is realized by the MAX266 company's switched capacitor type pin programmable integrated filter MAX266, which has better performance than the ordinary RC filter circuit.

The A/D conversion uses the 12-bit ADC with a maximum rate of 200 KSPS from the MSP430FG4619IPZ. Its voltage reference can be selected as an internal reference or an external reference, saving the external ADC chip, greatly simplifying the hardware design and satisfying the accuracy. Required, so it is very suitable for the design of this system.

3 indicator light and liquid crystal display circuit

The indicator circuit has three indicators of red, green and yellow. The red light is the power indicator light. When it is working, it is bright. The green light is the detection indicator light. Because the alcohol probe needs a certain time to heat up, the ideal sensitivity can be achieved. When the heating time is up, the green light is on. It means that the concentration detection can be carried out; the yellow light is the alarm indicator light, the yellow light is not bright, indicating that the vehicle can be driven; when the yellow light is on, it indicates that the alcohol concentration exceeds the standard and cannot be driven, and the higher the frequency of the yellow light flashing, the higher the alcohol concentration.

A liquid crystal display circuit is used to display the concentration of the measured alcohol. The liquid crystal display circuit adopts LCM128645ZK, which is a low-power dot-matrix LCD. It can work in 3.3V power supply, and the display format is 128 (column) × 64 (row). It has multi-function instructions and internal belt. There is a Chinese character library, which can work in both serial mode and parallel mode, and is easy to connect with a 16-bit microcontroller. The connection between the system and the single-chip microcomputer adopts the parallel working mode, as shown in Fig. 4.

Figure 4 keyboard display and indicator circuit diagram

4 relay control circuit

This circuit is controlled by the single-chip microcomputer P2.4, which is equivalent to the switch, which controls the opening and closing of the ignition device, the illumination of the lamp and the ringing of the speaker. It is a very important execution unit in the system. The circuit is simple, due to space reasons, it is not given here.

5 alarm and keyboard circuit

The buzzer is used as an alarm device, and when the alcohol content exceeds the standard, the prohibition driving warning sound is issued; when the standard is not exceeded, the permission driving sound is issued. This is achieved by driving the buzzer with P1.7.

Because the MCU has enough I/O pins, the keyboard circuit of the system uses a free-standing keyboard, as shown in Figure 4. Working in an interrupted manner, you can set the system parameters of the alcohol detection controller, such as the alcohol concentration of the alarm set.

6 other circuits

The JTAG interface circuit is used to debug the program and upgrade the system software. The power conversion circuit is used to convert the power supply system on the vehicle to the voltage required by the microcontroller and the chip used by the system. The monitoring reset circuit is used to ensure that the MCU is in a good operating state, preventing the program from running due to interference, and is more reliable than the internal watchdog circuit.

Through the above design, the front end of the system can control the alcohol content signal detected by the alcohol sensor through the single-chip microcomputer to generate a corresponding control signal to control the ignition circuit of the automobile, thereby realizing effective control of drunk driving.

software design

The software part is modularly programmed according to system functions. The main program flow chart of the controller is shown in Figure 5.

Figure 5 main program flow chart of the controller

Realize the detection of alcohol content, whether the alcohol content exceeds the standard, the alcohol content display, sound and light alarm and other functions. After the system is initialized, the alcohol sensor is heated and automatically enters the measurement state, and then the alcohol content voltage signal is collected and compared with the set precision concentration. If it is higher than this concentration, the concentration is displayed, and the sound and light alarm is performed, and the signal is cut off simultaneously. In the ignition circuit, the driver cannot start the car; if it is below this concentration, the measured concentration is displayed and the engine is started.

Conclusion

The onboard alcohol detector is designed to prevent traffic accidents. This article introduces the entire design by explaining the various circuit functions and software workflows. Because the system is installed in the car, the automatic measurement, high degree of intelligence, low power consumption, has a good effect on preventing drunk driving, and has a good promotion value in practical applications.

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