Theses and Dissertations

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Theses and Dissertations (Electrical and Electronics Engineering)

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Open Access
Development of a Synchronous Data Transmission System.
(Obafemi Awolowo University, 1986) Agomo, Uchenna Udochukwu; Kehinde, L. O.
The development of a 2 - channel synchronous data transmission system is presented. The system is capable of accepting at the input two separate analog voltage signals that have zero to 1 kHz frequency range and amplitude not greater than 2.5 volts. The two analog voltage signals are multiplexed at the input of the-system and converted to corresponding digital representations. These digital representations are then transmitted by means of digital gates from the transmitting section serially and with transmission clock frequency of 6.6 MHz, through cable wire to a remote receiving section, where the received digital representations are re-converted to analog voltage signals and demultiplexed to produce at the output, two separate analog voltage signals plus noise. The noise level does not exceed 5% of the signal level when filtered and leaves analog voltage signals with the same characteristics as those at the input of the system. The designed system is simple and can be used for laboratory demonstration on synchronous data transmission system. It may be useful as a communication medium for data exchange between two data processing terminals. The system may be used to transmit voltage signals from a central storage facility to a remote destination. In such circumstance the signals may be those derived from research results, medical findings and student/staff records. A computer base may then be set up and made accessible to users.
Open Access
Modelling of Raindrop Size Distribution in Nigeria for Microwave and Millimetre Wave Application.
(Obafemi Awolowo University, 1986) Adimula, Isaac Abiodun; Ajayi, G. O.
Raindrop size data collected using a distrometer measuring system at three geographical locations in Nigeria namely Calabar, Ile-Ife and Zaria have been analysed for the prediction of rainfall attenuation at centimeter and millimetre wave frequency bands. The modeling of the raindrop size distributions has been carried out using the lognormal and exponential distributions. Models for the three stations as well as a Southern, Northern and a general model for the country have been proposed for the prediction of the effect of tropical rainfall on electromagnetic propagation at microwave and higher frequencies. Rain induced specific attenuation values were computed for a frequency range of 1 to 400GHz using the models obtained for thunderstorm and shower which are very important for communication systems design.
Open Access
Design and Construction of an Electronic Heart Beat Monitor.
(Obafemi Awolowo University, 1986) Oladunjoye, Olunu Akintunde; Kehinde, L. O.
The design of safe monitors of physiological events in humans is of paramount importance in the field of medical electronics, and this report describes the development of a safe computer-based heart beat monitor for hospital use. The heart beats are detected by passing light through a finger into a photo-diode. Each time the heart beats, it pumps blood round the body and this causes the density of many parts of the body to vary, particularly the finger tips. By passing light through the finger tip onto a photodiode, this variation in density is converted into electrical signal that varies with the heart beat. The output of the photodiode is amplified in detection and amplification circuit to produce a CMOS compatible pulse each time the heart beats. An electronic method that does not employ a computer is first designed as a basis for comparison with the computer based method. In this method the time interval between successive three heart beats is measured and on the basis of the measured interval, the heart rate is computed by employing digital division method. This method, like others employing digital division method in computing the heart rate, has a reliable narrow operating frequency from 40 to 200 BPM, and a resolution of IBPM. Its main problem arises from truncation error. In the computer based method, the heart beat detection and amplification circuit is interfaced with a digital micro-computer. The microcomputer is programmed to measure the time interval between successive three heart beats, to compute the heart beat rate and to provide both graphical and numerical indications of the heart beat rate. This method has a wide operating range (10 to 10920 BPM), and a resolution less than BPM.
Open Access
Development of a Rainfall Attenuation Map for Microwave Terrestrial Application in Nigeria.
(Obafemi Awolowo University, 1987) Anazodo, Chiedu Charles; Ajayi, G. O.
The growing need to utilize frequencies above 10GHz for high capacity terrestrial and space radio links due to the congestion at low frequencies has enhanced the necessity to develop a map of attenuation due to rainfall at these frequencies. There is a dearth of instantaneous rainfall data in Nigeria hence the long-term total rainfall data and other meteorological data obtained from some 37 stations in Nigeria have been used to study the attenuation due to rainfall for microwave terrestrial applications in Nigeria. A database has been created for all the data and statistical analysis carried out on them. The Dutton and Dougherty (1974) prediction model used for predicting short integration time rainfall rate from long-term rainfall data for Europe has been modified for use in the Nigerian climatic conditions. Regression techniques have been utilized to obtain a mathematical relationship between the rainfall rate, the average annual rainfall and the number of thunderstorm days for all the available meteorological stations. The computed one-minute integration time rain rate has been used to predict the specific attenuation for some microwave frequencies for each station and the results are presented in form of contour maps. The attenuation map shows that specific attenuation due to rainfall is higher in the southern parts of Nigeria compared with the northern parts. The results obtained in this study will be useful in the design of terrestrial microwave links in Nigeria, especially in the estimation of necessary fade margin to take care of attenuation due to rainfall.
Open Access
Rainfall Attenuation on Earth-Satellite Microwave Link in a Tropical Environment
(Obafemi Awolowo University, 1987) Odunewu, Paul Adekunle; Ajayi, G.O.
Rainfall is a major impairment to radiowave propagation at centimeters and millimetre wavebands, moreso in the tropics because of the intensity, frequency of occurrence and presence of large drops in tropical rainfall. In order to determine the vertical extent of rain (rain height) in the tropics, the characteristics of 0°C isotherm height have been studied using radiosonde data collected at three stations in Nigeria for three years at each station. One year rain rate data collected at Ile-Ife using an electronic rapid response rainguage have been analysed in order to obtain the cumulative rain rate distribution. The existing rainfall attenuation prediction models have been examined. Three attenuation models viz: CCIR, Global and SAM, have been utilized to predict slant path attenuation at Ile-Ife from the one-year rain rate distribution. Cumulative distributions of predicted attenuation were obtained for different frequencies, earth station's elevation angles and polarizations. Attenuation distributions from the three models have been compared. The result obtained shows that 0°C isotherm height during rainy season decreases from the southern to the northern part of Nigeria. A mean 0°C isotherm height of 4. 8 km for the rainy season has been obtained for Nigeria. The rain intensity exceeded for 0.01% year at Ile-Ife was obtained to be 87 mm/h. The differences in the attenuation values predicted by the three remodels vary for different percentages of time, frequencies, elevation angle and polarizations. The results obtained in this work could be used for providing necessary fade margin in satellite link budgets in Nigeria and other similar tropical environment.
Open Access
Development of a Text-Independent Speaker Identification System
(2015-04-22) Fisusi, Abimbola Adeola
Access control to confidential information and facilities is conventionally through the use of passwords, smart cards or keys that can be stolen or forgotten. In this work, a software-based access control system that identifies users by the unique features in their voices, which cannot be easily breached, was developed with a view to overcome the limitations of conventional access control methods. The implementation of the system involved two phases - the training and testing phases. During the training phase, speech samples were collected from seven male and five female speakers by recording their voices with a microphone connected to a computer system. Speaker's unique features were extracted from the speech samples in form of Mel-Frequency Cepstrum Coefficients (MFCCs) which estimated the unique shape of the spectral envelope of each user. The extracted MFCCs features were used to build speaker models in form of codebooks for the speakers using the Vector Quantization (VQ) approach. The speaker models created were stored in a database. During the testing phase, another set of speech samples were collected from the same set of speakers of the training phase. MFCC features were extracted from each of the testing speech samples and compared with the codebooks created during the training phase. For each testing speech sample, the speaker whose codebook gave the lowest average distortion was identified as the true speaker. Codebooks of different sizes ranging from 16 to 256 were used to perform the identification task. In the same vein, the performance of the system as a text-dependent system was also evaluated using the same words for both training and testing phases. The performance of the text-independent speaker identification system was evaluated by comparing the speakers' testing phase MFCCs with their training phase codebooks. The results showed that the identification rate of the text-independent speaker identification system increased with increase in codebook size. "The identification rate of the system was 57.14% when 16-vector codebooks were used as speaker models. It was 71.43% and 85.71% for 32-vector and 64-vector codebooks respectively. The speaker identification system was able to achieve 100% identification rate at codebook sizes of 128 and 256. The average distortions of speakers from testing speech samples were found to decrease with increase in codebook size. The 128-vector codebooks are preferred over 256-vector codebooks because the time required to perform the identification task is shorter for 128-vector codebooks although both give 100% identification rate. 1n conclusion, the developed text-independent speaker identification system could distinguish between speakers correctly and provide security for confidential information and facilities better than conventional methods if the codebook size used for the identification task is large enough.
Open Access
Development of a Self-Coordinated Communication System for Scaring Birds on Rice Farms
(2015-06-23) Badru, Rahmon Ariyo
The study appraised techniques for communicating hazards to birds and developed a self-coordinated electronic communication system for scaring birds. It also determined the optimal placement of the bird-sensory electronic devices on the rice farms. This was with a view to solving the problem of menace of birds on rice farms. Static (e.g. scarecrow) and dynamic (e.g. drumming) methods of communicating hazards to birds through their tactile sensory cells bristle feathers, vibration sensors (Herbot's corpuscles), hearing tubes, rods and cones sensory cells were appraised in relation to their practical implementation and cost effectiveness. A prototype system was simulated by designing an infrared (IR) transmitter and receiver circuits, which were constructed using relevant combination of electronic techniques. Subsequently, an electronic IR motion detection system comprising of pyroelectric infrared sensor, Fresnel’s lens, amplifier and comparator circuits were developed and implemented. In addition, the architecture of the system was fitted with air vibration mechanisms human eye-structured and sound producing units. The overall assembly was covered with sheet of rust-free metallic sunlight reflector. The results showed that the effective coverage field and detection range for the simulated IR transmitter and receiver system were 10° and 1.5m respectively. This system was characterized with low quality siren output, faulty triggering during systems stand misalignment and inability to electronically facilitate other actuators for the effective scaring of birds. Furthermore, the self-coordinated communication system had a coverage field of 95° and a detection range of 27.4 m. The prototype of this system was observed to scare birds when the air vibration mechanism produced artificial oscillation of air molecules. The illumination produced by the human eye-structured unit coupled with the reflection of diffused sunlight rays from the body of the system disturbed the sight of the birds. Also, sound of triangular waveform signals with frequencies from 0.6 kHz to 1.5 kHz in periodic bursts of 3.0 seconds was interpreted by the birds as scare signals. In conclusion, the device was found to be suitable for the communication of hazard to birds attacking rice plants which is fundamental to improving the yield per hectare of the protected area.
Open Access
Design and Simulation of a Programmable Logic Controller for Remote Monitoring and Control of Satellite Oil and Gas Wells
(2015-09-30) Ikono, Nsikan-Abasi Michael
This study investigated development of an automatic controller for remote production restoration of oil and gas wells with a view to minimizing downtime by giving electronic logic alerts of problem areas to the system operator. The conceptual design was based on the development of a ladder logic circuitry with variable input data such as high pressure, low pressure and valves position signals sensed as "ON" or "OFF" signal levels. These input data were scanned at predetermined time intervals using the Programmable Logic Controller (PLC). The "TRIlogi 5.3" educational computer application simulator was used to simulate the workability of the ladder logic program. A remotely operated PLC system constructed with transceivers was used to demonstrate the operations by running the ladder logic program with physical model using On/Off switches as inputs and light emitting diodes (LED) as output indication. The results showed that operating the PLC logic program can achieve input variable monitoring by indicating the current statuses of the inputs with "ON" state as high pressure, "OFF" state as low pressure and "ON/OFF" as opened and closed valve positions respectively. The simulator did not require any physical connection to the target PLC, thereby offering the most effective way of testing and debugging ladder logic program prior of the hardware. Programming and debugging time were greatly reduced by making good use of the simulator feature to eliminate as many logic errors as possible before testing the program on the actual hardware. In addition, it reduced the chances of costly damage to the PLC machine due to programming errors. Moreover, it controlled the opening and closing of well production with the PLC output signals acting as feedback from the logical decision to operate end devices actuator coils with changed statuses indicated by the output LED. In conclusion, the result of the system test established the workability of remote restoration of oil and gas production using a PLC for quick decision making.

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