Automobile alcohol detection kit with speed limiter

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1. System Specification


At present drunken drivers have increased enormously and so is the deaths due to drunken drivers. The main reason for driving drunk is that the police are not able to check each and every car and even if they catch any one the police can be easily bribed. So there is a need for an effective system to check drunken drivers.

In our alcohol detection system the ignition of the fuel is regulated by a sensor circuit. The sensor circuit is used to detect whether alcohol was consumed by the driver recently. Our design also consists of a blood pulse rate sensor which is used to check whether alcohol is consumed while driving. If the breath sample contains no alcohol, the driver is given full control to the speed of the automobile.

System aim:

The aim is to monitor the alcohol level of a driver through the breath sample taken and:-

  1. Prevent the driver from driving if the alcohol level is over the legal limit.
  2. Limit the speed of the automobile if the breath sample contains alcohol but less than the legal limit.
  3. Give full control if no alcohol is detected.


  1. Design: Small in size, save space.
  2. Where: Place the alcohol tester nearby the steering for neat and convenience purposes. The pulse rate sensor is placed inside neck cushion.
  3. Detection: The pulse rate sensor is sense continuously to prevent driver take the alcohol drink during driving.

2. Proposed solution

2.1 Specification of solution

Descriptions of individual modules:

Alcohol breath sensor

Breath alcohol sensor (BATs) depends on the blood to breath ratio. 2,100 ml of a deep air lung sample contains the same amount of alcohol as I ml of blood. This sensor uses infrared light to detect alcohol content. This device passes a breath sample through a narrow band of infrared light set to a frequency absorbed by alcohol. The amount of infrared light not absorbed by the alcohol tells the concentration of alcohol in the breath. The output voltage varies proportionally to the input alcohol concentration. The maximum output voltage is set to be the legal limit of Blood Alcohol Content in a country. Any input of alcohol concentration higher than the legal limit will produce a constant output voltage (maximum output voltage).


Analog-to-digital converter. Receives analog signal from alcohol breath sensor and quantize it into 3 bits binary code. The output is in the form of alcohol level per code. The ratio of quantize is preset by reference to the maximum alcohol level acceptable (legal limit of a country).

CO2 sensor

CO2 can be sensed by a ceramic sensor. The CO2 sensor consists of a testing chamber and a ceramic sensor. The sensor compares the carbon-dioxide level in the test chamber with that of pre programmed value. When the CO2 level in the test chamber is higher than the pre programmed value, the sensor will send a high voltage signal continuously to the timer until the CO2 level drops.

Pulse Rate Sensor

The pulse sensors consist of piezo electric transducer. The piezo electric transducer can sense small mechanical vibrations produced by the blood pulse which is sent to the microprocessor in the form of digital signal. When a person gets drunk his pulse rate increases. This principle is used in the detection process while driving. However the pulse rate may vary from person to person so when the driver has passed the test at the time of starting the car, his pulse rate is noted as the reference pulse rate. The pulse rate is then periodically checked and if there is a drastic increase in the pulse rate the automobile will be limited to the lowest speed unless the driver stops the automobile and goes through the alcohol detection process again.

Automobile Battery Switch

The battery supplies large power to the spark plug, so direct interfacing of the logic circuit will burn the IC, thus relay switch are used. The battery switch consists of a NC relay switch. The NC switch is controlled by a solenoid which is energized by the signals from the logic circuit. The power for energizing the coils is obtained by amplifying the IC signals using a transistor. When the output from the control unit is high, the switch is closed and the ignition can be started. Otherwise, the ignition will be locked as there is no power to the spark plug (switch opened).

Actuator interface

The actuator interface reads output from the control unit in the form of 3-bits binary code and converts it into analog signal. The signal is then amplified using a transistor to drive the speed limiter actuator. Higher signal means higher alcohol level detected, and thus more speed will be limited.

Speed limiter actuator

The speed limiter hold the accelerator pedal in a decelerating position by a force produced by an operating fluid pressure which is proportional to the voltage signal from the actuator interface. A pressure relief valve is provided to absorb a strong depressing force exerted by the driver to the accelerator pedal.

Control unit

The control unit uses 3 input ports and 2 output ports. First input is from CO2 sensor part. The control unit will start receiving second input from alcohol breath sensor part only when it receives high signal from the first input (CO2 sensor) continuously for 5 seconds. This makes sure that the breath sample taken is from the lungs instead of the mouth during the alcohol detection process.

Depending on the second input (alcohol breath sensor), there will be different output. The second input signal is in the form of 3 bits binary code. If the second input signal is 111 (alcohol level is higher than legal limit), there will be no output to the automobile battery switch and the relay will be opened, hence the ignition cannot be started. If the second input signal is 000 (no alcohol detected), the there will be a high output signal to the automobile battery switch and the relay will be closed, hence the ignition can be started. Any other input signal is sent directly to the actuator interface for decoding.

After the ignition is started, the control unit will receive input periodically from the pulse rate sensor part. The signal is then processed and pulse rate is calculated (number of pulses by time). The initial pulse rate is taken as reference and periodic checks are made by the sensors, if there is drastic increase in pulse rate, the automobile will be limited to the lowest speed (output of control unit to actuator interface is 110).

High input from CO2 sensor for 5 seconds

Alcohol breath sensor

Output to Automobile Battery Switch

Output to Actuator Interface













Truth Table 1

Note: X = any input

Qin = Qout (any input except 111)

Power supply

The supply is taken directly from automobile battery. The voltage supplied into the logic circuit is stepped down using a 5V regulator.

2.2 Method of testing and system verification

  1. Testing of individual block
    1. Alcohol breath sensor: Apply different concentration of alcohol breath and monitor its output. The maximum output (legal limit) is recorded to preset the ADC for quantize purposes.
    2. CO2 sensor: Monitor its changes in output before and after exhaling breath to it.
    3. Pulse Rate Sensor: Put the sensor at the wrist or neck and monitors its output.
    4. ADC: Apply different level of voltage to it and monitor its output in the form of 3 bits binary code.
    5. Automobile Battery Switch: Monitor the condition of switch before and after applying voltage to it.
    6. Actuator interface: Apply different binary code input and monitor its output voltage (should be increasing proportionally to the binary code value).
    7. Speed limiter actuator: Connect to the actuator interface and monitor its changes in height after applying different binary code input (should have higher height for higher value of input).
    8. Control unit: Test alcohol detection part and pulse rate sensor part individually.
  2. For alcohol detection part, input is and output value should be as shown in Truth Table 1 (section 2.1).
  3. For pulse rate sensor part, apply an initial digital frequency to the input and change the applied frequency drastically and monitor its output on the actuator interface (output should be 111).
  4. The complete system is installed on an automobile and all possible input is tested for required output.
  5. Dynamic testing of the speed limiter part on the road. Both input from alcohol detection and pulse rate sensor is utilized and tested for required speed limit.
  6. Supply automobiles with the system fitted to selected commercial users for their evaluation and comments.

3. Resources required

3.1 Major components


Price (US Dollar)


CO2 Sensor



Alcohol Sensor



Pulse Rate Sensor



8 bit ADC Converter



Battery Switch






Speed Limiter Kits



5V Regulator



3.2 Design and implementation tools

  1. Microcontroller code development tools:-
    1. Microsoft Visual C++
    2. PIC Compiler
    3. PIC Programmer
    4. PIC Development Board
  2. PCB design tools and manufacturing facilities
    1. Eagle 5.0
    2. Multisim 10.0
  3. Testing tools
    1. Multimeter

4. Time plan














Preliminary Design

Detailed Hardware Design

Detailed Software Design

Complete Sensors Part

Complete Actuators Part

Complete Control Unit Part

Build System

Test System

User Trials

Preliminary Design: Brainstorm the design and rough out the top level design.

Detailed hardware design: Obtain the components and complete the detailed design of the hardware.

Detailed software design: Complete the detailed design of the software.

Complete Sensors Part: Complete building and testing of all required sensors.

Complete Actuators Part: Complete building and testing of actuators part including actuator interface.

Complete Control Unit Part: Complete coding and testing of the microcontroller.

Build System: Combine all sub-parts into a complete system.

Test System: Test the completed system.

User Trials: Supply automobiles with the system fitted to selected commercial users for their evaluation and comments.

5. Conclusion

Overall, this project is a system that consists of few types of sensors. The cost of this system is approximately about $70. With this system, the number of accident can be reduced. Besides, it also can help the driver to save their compound that cause by driving in drunk. This system must be installed on every car because life has no take two.

6. References