Microcontroller Based Instrumentation in Automotive Engineering

Microcontroller Based Instrumentation in Automotive Engineering
Abstract:
Microcontroller is a standalone device that is used to control the operation of a piece of equipment. This involves sensing simple parameters and controlling of events. This article presents an overview of how microcontrollers, ‘computer on a chip’, are used in automotive applications, i.e. in intelligent vehicles. The approach we use is to first provide a framework why microcontrollers are used in instrumentation, how systems work, why not microprocessor, current market trends, diagnosis process and several other applications.
1.1 Introduction:
Instrumentation is a technology of measurement, analysis, and control which serves not only science but all branches of engineering, medicine and almost every human endeavor. The basic purpose of instrumentation in a process is to obtain requisite information operating to the fruitful completion of the process. The object of fruitful completion, in industrial technology, is obtained when process efficiency is maximum with minimum cost of product quality. A microcontroller can be found at the heart of all such electronic control module in all process industries today. One most important advantage in using a microcontroller in the system may be, designed to eliminate human factor in processing data. The prime use of microcontroller is to control the operation of a machine using a fixed program that is stored in EEPROM and that does not change over life time of system.
1.2 Reason behind Choosing Microcontroller in Instrumentation:
The major reasons for digital microcontroller based control system are

A. Stability and accuracy of control B. Lower cost per function C. Flexibilities D. Greater reliabilities and equipment life E. Human factors favoring digital interface.
In process control using electronic controllers there are lots of hardware as shown in Fig1. Process performance totally depends upon the characteristics. Process accuracy is less and operation is not very fast. For a simple modification we have to change total hardware design which is very costly and time expansive.

Fig.1. Close Loop System Using Op-Amp.
In microcontroller based systems, total hardware of control system is replaced by microcontroller unit. By a little change in program we can change system operation. Less hardware is required in this case as shown in Fig2.

Fig 2. Close Loop System Using Microcontroller Unit.
Market Trends:

Fig3. Market Trends of Microcontroller Based System:

1.3 Basic Scheme:

Fig4. Basic Scheme
Measurement and control of physical quantities such as temperature, pressure, speed, displacement, level flow etc. is done with transducers which are used to control the physical quantities to electrical signals. The electrical voltages proportional to the physical quantities by an ADC before is applied to microcontroller. A microcontroller being very fast can measure, process and control
many signals one by one in a very short time according to the program fed in it. The output from the microcontroller is used to control different process accurately, by means of controlling different device like relays, motors, actuators etc.

1.4 Why Microcontroller, Not Microprocessor:
Microprocessor is a general purpose device .It requires lots of extra peripherals which make system complicated and system size become large and bulky. Whereas a microcontroller is used for specific operation. For small systems there is no necessary to use microprocessor as it become expansive and bulky. In microcontroller all peripherals required in microprocessors are contained in a single chip, called microcontroller. For e.g. in a simple smart washing machine, it is not necessary to use a big computer for its operation, a single 4-bit microcontroller can easily do all the work what we require. Microcontroller can function as a computer with the addition of no external digital parts.

1.5Application of Microcontroller Based Instrumentation in Automotive engineering: A microcontroller can be found at the heart of almost any automotive electronics control module or ECU in production today. Automotive system such as Anti-lock braking system (ABS), Cruise control, engine control, navigation and vehicle dynamic all incorporate at least one microcontroller within ECU to perform necessary control functions.
1.5.1 Engine Control:
The electronic engine control system consists of sensing devices which continuously measure the operating conditions of the engine, an electronic control unit (ECU) which evaluates the sensor inputs using data tables and calculations and determines the output to the actuating devices which are commanded by the ECU to perform an action in response to the sensor input. The motive for using electronic engine control system, ECU is to provide the needed accuracy, adaptability in order to minimize exhaust emission, fuel consumption fuel metering and ignition control. An information on the failure from the ECU and correct the problem. ECU (microcontroller) performs following operation in this section:
1. Air/fuel ratio control. 2. Ignition timing control 3. Exhaust gas recirculation control & monitoring. 4. Idle speed control 5. Fuel system monitoring 6. Diagnosis.
1.5.2 Cruise Control:
A sophisticated digital controller constantly maintains a set speed under varying driving conditions, thus allowing the vehicle operator to index from constant foot throttle manipulation and improve fuel efficiency. By using the power and speed of microcontroller device and fuzzy logic software design excellent cruise control system can be designed. The MCU for cruise control applications requires high functionality. The MCU would include the following:
1. A precise internal time base for the measurement calculations. 2.A/D inputs
2. 3. PWM outputs 4. Internal watch dog 5. EEPROM
Crash avoidance system could be inter connected with cruise control system to avoid collision and

Fig.5 Engine and Cruise Control Parameters
warn the drivers.
1.5.3 Anti-Lock Braking System:
ABS consists of wheel speed sensors, hydraulic modulator, electric / pump and ECU (microcontroller). Control of hydraulic modular and electric motor / pump is performed by the electronic unit. Microcontroller based ECU performs braking operation most accurately.
1.5.4 Intelligent Safety System:
Electronically controlled passenger and car safety systems, such as rollover sensors system, air bags, seat belts tension system, help to avoid injuries or to reduce injury severely in an accident. In ISS, vehicle has collision avoidance that takes necessary actions like reduce speed or apply brake, and also warn the driver and order to take action. The sequence of crash relevant events like closure of discriminating sensors , arming sensors, battery voltage level, energy reserve voltage, turn on of power stages, can be stored in the EEPROM i.e. record present conditions of the vehicle before crash.
1.5.5 Vehicle Antitheft System:
To avoid vehicle thefts, we must do three things: sense unauthorized entry of the vehicle, detect unauthorized empted to starts the vehicle and activate the alarm system. Some fixed or rolling codes are
store in EEPROM of microcontroller. When those code matches with user code, system allow using the

Fig 6: Method for Arming and Disarming an Antitheft
vehicle otherwise alarm system activated.
1.5.6 Voice Alarm:
Inputs from sensors are fed to the microcontroller unit. MCU continuously compare the input values fro sensors with the set point value and maximum allowable value stored in EEPROM. if the exceeds the maximum limit , then microcontroller send a signal to voice module which gives recorded message to take necessary action.
1.5.7 Navigation:
Military, as well as civilian, vehicles need to be guided, located, or to navigate or position them independently. Navigation pertains to the actions involved in driving a vehicle from point to point. Aerospace/military guidance and navigation applications require advanced inertial sensors with high performance (e.g., very high intrinsic stability, rectification error), advanced functionality (digital output, correction for temperature effects), and shock survivability, as well as sensors that are lighter, smaller, and cost less than typical existing technologies. Moreover, such parameters as mission time, expected precision, dynamic range, and harsh environmental conditions (temperature, shock, etc) are important to measure in inertial navigation systems. By using the advantages of modern communication system and instrumentation technology navigation process is done which helps to know on line traffic condition, road condition etc.
1.6 Diagnosis Process:
In order to minimize the number of defects or even to completely avoid them, a vehicle requires regular
checks. In case of an inevitable defect, a clear and directed diagnosis is required and has to follow by prompt, reliable and inexpensive repair. For an effective and successful diagnosis following tasks are involved

Fig8. Operational Sequence in Microcontroller
1. Fault storage with boundary conditions. 2. Fault localization. 3. Data correction, recognition of imminent faults.4. Parameter substitution. 5. Providing guidelines. 6. External diagnosis
1.7 Other most widely used applications:
1. MEMS accelerometers, flow meters use a microcontroller.
2. Analytical instrumentation.
 UV and X-rays silicon pixel detectors, micro-fluidics, micro-electrodes arrays in gold, platinum or titanium, micro-coils and micro-magnets, arrays of micro holes and micro-heaters.
 Higher - power deep UV (ultraviolet) exciter lasers that utilize beam shaping and coherent power combining techniques. ; X-ray, chromatography, NMR, spectrometer.
3. Medical instrumentation.
 TFT laser annealing, and ophthalmic surgery.
 In the life sciences arena, Colibrys has ability in combining micromechanics, micro fluidics,
micro magnetic, micro optics, and single photon counting detectors.
4. Aerospace/defense applications.
 Radar control. ; Guided missile control;
 Satellite launcher.
1.8 Pros and cons:
Pros: Stability and accuracy of control system increase.
 Integrated features onto microcontroller allow the system designer to reduce cost else where in the system.
 Very compact circuitry as single chip contents all peripherals.. System flexibilities are very high.
 The high speed (24-32 MHz) operation feature of microcontroller allows more code to be executed and thus system performance improves.
 System security is very high as individual manufacturers uses own fixed program, and stored in ROM, any other manufacturer can not use the same program.
Cons: Noise in the system can affects on the performance.
 Servicing is not possible by general user; replacement of chip is the only solution.
1.9 Conclusion:
The desire for greater safety, comfort, and environmental compatibility is leading to a rapid increase in electronic control units and sensors. Smart vehicle is one of the most common applications where microcontroller based instrumentation is widely used. By the use of microcontroller based instrumentation, process become more accurate and easy to design. Adding little bit modification in program we can add various features in control system without changing any hardware. As the hardware technology developing very rapidly , more and more feature included in the microcontroller that give process designer more flexibility to design a system in a simple manner., and larger than large system becoming smaller than small with very user friendly manner.

Reference:
1. Ronald Jurgen, “Automotive Electronics Handbook”. chapter 11 ,12,13, 14,15,22,23,24
2. Automotive Engineering International (SAE), September 2000.Delphi’s Integrated Safety System
3. .Kenneth J. Ayala ‘The 8051 Microcontroller
4. D. Patranabish ‘Principles of Industrial instrumentation’
5. Sensor Business Digest , April 2003
6. Integrated Circuit Engineering Corporation; ‘Microcontroller Market Trends’ ‘SEC03’page15