UNIVERSITY OF NAIROBI Department of Electrical & Electronic Engineering A FOUR CHANNEL-D MICROCONTROLLER BASED DATA ACQUISITION SYSTEM WITH A SERIAL INTERFACE TO THE PC Project No.061 LENNOX ABONG’O OGOLA F17/2040/2004 Supervisor: Mr.Collins Ombura Examiner: Dr. H.A. Ouma

OBJECTIVES To design and implement a four channel –D microcontroller based data acquisition system with a serial interface to the PC Employ a graphical user interface to display the data transmitted to the PC

INTRODUCTION The function of the data acquisition system (DAS) is to convert signals from the real world analogue domain to digital domain for processing by the digital electronic systems. The fundamental operation of DAS is quantization, whose result is transmitted to the PC through serial interface.

DATA ACQUISITION SYSTEM

SENSORS  These are measuring instruments used to read values within the range of their measurements.  Process variable sensors include: temperature sensors-LM35DZ flow rate sensors -vortex shedding pressure sensors-strain gauge diaphragm level sensors-displacement float

INTERFACING SENSORS TO AVR MICROCONTROLLER The sensor has the primary element and the signal conditioner, The output of the primary element is a measure of the variable it is sensing, but it is not usually in a suitable form for transmission signal. Hence a conditioner is required to convert it into a suitable value. The standard transmission signals are 4-20mA electric current or 0-5v.

ADVANTAGES OF THE SYSTEM The microcontroller design technique employed reduces the external support circuitry thus reduces much work involved in circuit design The addition of more channels to the system is done within the program which makes the system flexible to design modifications Higher accuracy due to accurate sensors used and digital data processing.

DESIGN AND IMPLEMENTATION Specifications of design Sensor: LM35DZ temperature sensors AVR Microcontroller: Atmega168 20PU Line Driver: MAX232N. DB9/F Connector

SCHEMATIC DIAGRAM

THE ADC CONVERSION FLOW CHART

ADC CONVERSION This forms the core of the system, the flow chart shows the routine to start A/D conversion It preloads the counter with and starts counting up at frequency XTAL/8 The conversion complete flag is cleared and the result is sent to the ADC data register ready for transmission.

PROGRAMMING ATMEGA168

RESULTS CHANNEL_1 TEMPERATURE READINGS

CHANNEL_2 TEMPERATURE READINGS

CHANNEL_4 TEMPERATURE READINGS

CHANNEL_3 TEMPERATURE READINGS

ANALYSIS OF RESULTS The windows HyperTerminal was used to display the data transmitted to the PC since this would make the user comfortably user the system without need of installing VB.NET The temperature measured by the LM35DZ sensor were of averaged Tav=sum of the readings/number of the readings this was found to be 27degrees centigrade. The result compared well with the room temperature of the day.

CONCLUSION The results give by the system determined the measurement of the physical phenomena- temperature. It also enhanced accurate measurements with a high response to any change in the parameters of the phenomena.

RECOMMENDATION Recommendation: The addition of more sensors to ensure that all the ADC channels are used, Duplex communication between the microcontroller and the PC to enhance execution of commands from the PC as well based on the data it receives.

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