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Öğe Adaptive thresholding based low complexity QRS detection algorithm(2023) Karakulak, ErtuğrulIn this study, a QRS detection algorithm with a low processing load based on time-domain thresholding is proposed. The ECG signal is filtered only with a low pass filter to reduce the computational load. After the filtering, derivation and squaring are also performed. In the Thresholding stage, a linear decreasing threshold voltage method using addition operation instead of multiplication is proposed. Simulations on MIT-BIT Arrhythmia Database have yielded 99.2925% sensitivity (% Se) and 99.6759% positive predictivity (+ P). The proposed algorithm is compared with two similar algorithms in terms of both performance and processing load. It is shown that the proposed algorithm is better than its counterparts, especially in terms of processing load. However, it is observed that it gave worse results in terms of Sensitivity (% Se).Öğe ANN Circuit Application of Complementary Resistive Switches(2019) Uçar, Erdem; Karakulak, Ertuğrul; Mutlu, ReşatArtificial neural networks are successfully used for classification, prediction, estimation, modeling and system control. However, artificial neural networks integrated circuits are expensive and not matured enough. Memristors or memristive systems which show a nonvolatile memory behavior has a high potential for use in artificial neural network circuit applications. Some memristive synapse or memristive neural network applications already exist in literature. The complementary memristor or resistive switch memories have been suggested as an alternative to one-cell memristor memories. Their sensing is more difficult and complex than the others. The complementary memristor memory topologies with a sensing node are also inspected in literature. To the best of our knowledge, a neural network circuit which is based on the complementary resistive switches with a sensing/writing node does not exist in literature yet. In this paper, several neural network circuits which are based on the complementary resistive switches with a sensing/writing node have been designed and examined for the first time in literature. Their analysis are given and simulations are performed to verify their operation. We expect that such a complementary resistive switch implementation may find use in artificial neural networks chips in the future.Öğe ARM MCU-Based Experimental EEG Signal Generator Using Internal DAC and PWM Outputs(Gazi Universitesi, 2022) Karakulak, ErtuğrulElectrophysiological signal generators are widely used in biomedical engineering research, biomedical education and the testing of devices in hospitals. Such signal generators are also available commercially. The EEG (Electroencephalography) signal is an electrophysiological signal which is emitted from the brain. In this study, a signal generator that produces experimental EEG signals taken from databases is proposed. The proposed signal generator reads the experimental data from an SD card with SDIO serial protocol. In addition, the PWM and DAC outputs of the microcontroller are used and examined separately to generate the signal. It has been shown that the experimental signals taken from the database can be generated by using cheap and easily accessible electronic devices. © 2022, Gazi Universitesi. All rights reserved.Öğe Emulator circuit of Ti02 memristor with linear dopant drift made using analog multiplier(2010) Mutlu, R.; Karakulak, ErtuğrulMemristors or charge-controlled memristive systems , are not available for experimental studies in market. In literature, emulators which mimicks memristor behaviour for studying and teaching of memristor do exist. In this work, for the first time in literature, a Ti02 memristor emulator is made by an electronic circuit with an analog multiplier. Using hysteresis and saturation phenomena, it is shown that this emulator can mimick Ti02 memristor with linear dopant drift speed well.Öğe Implementation of a Microcontroller-Based Chaotic Circuit of Lorenz Equations(2020) Yener, Şuayb Çağrı; Mutlu, Reşat; Karakulak, ErtuğrulLorenz equations are commonly used in chaos education and studies. Simulation programs can be used to produce solutions of Lorenz equations and to examine its chaotic waveforms. However, sometimes a chaotic signal source can be needed. Such a circuit can be made using either analog or digital circuit components. Recently, a microcontroller-based circuit is suggested to obtain chaotic waveforms of Lorenz equations however only simulations are used to show proof of concept. Such a circuit needs experimental verification. In this paper, implementation and experimental verification of the microcontroller-based circuit which solves Lorenz equations in real-time and produces its chaotic waveforms are presented. Runge-Kutta method is used to solve the equation system. By using Proteus, the microcontroller-based chaotic circuit is simulated and designed. The presented design has been implemented using an Arduino Mega 2560 R3 microcontroller. The microcontroller sends the chaotic signals to the outputs of the circuit using digital-to-analog converters. The waveforms acquired experimentally from the implemented circuit match well with those obtained from Proteus simulations.Öğe Implementation of Microcontroller-Based Memristive Chaotic Circuit(Polish Acad Sciences Inst Physics, 2017) Yener, Şuayb Çağrı; Barbaros, C.; Mutlu, Reşat; Karakulak, ErtuğrulIn 1971, Leon Chua theoretically postulated that the memristor is the fourth fundamental circuit element, besides the three well-known circuit elements; namely, resistor, capacitor and inductor. For a long time, because of lack of a simple and practical realization, memristor remained just a theoretical element and rarely appeared in the literature. In 2008, a research team from HP laboratories declared that they had found a physical implementation based on thin films, behaving as a memristor. Memristor can offer new opportunities in circuit design due to its nonlinear behavior and memory. Nevertheless, since a cheap and reliable practical implementation of memristor is yet unavailable on the market, the design of such a realization, which mimics memristor behavior, is vital from the point of view of real-world circuit design. In this paper, a new microcontroller-based memristive chaotic circuit is proposed. Presented design has been implemented using an Ardunio Mega board, which solves numerically the dynamics of the memristor-based chaotic system using Runge-Kutta method. It sends the chaotic signals to the outputs of the circuit, using digital-to-analog converters. Chaotic dynamics and the strange attractors are obtained from the circuit using both, the computer simulations and the lab experiments. Considering both simulation and experimental results, it is shown that the proposed circuit mimics well the dynamics of the memristive chaotic system.Öğe Memristor emulators with symmetric and asymmetric threshold voltages(IEEE, 2018) Mutlu, Reşat; Üstünel, Tayfun; Karakulak, ErtuğrulMemristor, a fundamental circuit element, was predicted to exist in 1971 by Leon Chua. Chua used an emulator to show how a real memristor would behave in 1971. A memristive system which behaves as a memristor for some part of its operation has been found in 2008. Unfortunately, not many research institutions or companies have a memristors available in their hands. That's why new types of memristor emulators have been done in literature for research and education purposes. Some memristors or memristive systems are reported to have a considerable threshold value. In this study, different memristor emulators with either symmetric or asymmetric threshold voltages have been made. Diodes are used to obtain these threshold voltages. Its analysis and experimental results are given.Öğe Memristör Tabanlı Negatif-Pozitif Kazanç Devresi(2018) Karakulak, Ertuğrul; Mutlu, Reşat; Uçar, ErdemMemristörler, doğrusal ve zamanla değişmeyen devre elemanları kullanılarak yapılamayacak bazı analog uygulamalar için büyük bir potansiyel vaat eden non-lineer devre elemanlarıdır. Bilimsel literatürde bazı memristör tabanlı filtreler ve yükselteçler gibi analog uygulamalar incelenmiştir. Eviren ve evirmeyen memristor tabanlı yükselteçler de literatürde incelenmiştir. Bu çalışmada, literatürde bir ilk olarak, hem negatif hem de pozitif kazanç verebilen, opamplı ve memristör tabanlı bir devre önerilmiştir.Öğe Memristor-Based Phase Shifter(IEEE, 2018) Mutlu, Reşat; Karakulak, ErtuğrulMemristor is a new nonlinear circuit element. It is a special case of memristive systems. It has a charge-dependent resistance and a frequency dependent hysteresis curve when excited with an AC source. It has been claimed as the fourth fundamental circuit element in 1971 and a solid-state thin film behaving as a memristor system is found in 2008. Following this discovery, memristor-based memories, neurons, ANN circuits, chaotic sources, analog filters and oscillators have become a hot research area and, if one day memristor becomes commercially available, it may give way to new types of analog applications due to its tunable resistance. In this paper, a memristor-based phase shifter circuit is examined for the first time in literature.Öğe Memristor-based series voltage regulators(Slovak Univ Technology, 2019) Yavuz, Kutluhan Kürşat; Karakulak, Ertuğrul; Mutlu, ReşatSeries linear voltage regulators are integrated circuits commonly used to make adjustable voltage sources. When used with potentiometers, these regulators are able to give adjustable voltage at the output. Memristor is a new nonlinear circuit element which came out in the last decade. It is able to provide electronically adjustable resistance. If a memristor is fed with a voltage over the threshold and it is not under saturation, its resistance also called memristance is dependent on the integration of its current, also called memristor charge. Memristor shows promise for different types and lots of digital and analog applications. In this paper, memristor-based series voltage regulator topologies are suggested and they are examined using parameters and simulations. Some design criteria have been given for the memristor-based series voltage regulators.Öğe Providing hand posture information via a 3-DOF tactile sensory substitution system(Institute of Electrical and Electronics Engineers Inc., 2020) Karakulak, Ertuğrul; Devecioğlu, İsmailMotorized prostheses provides functional improvements to their users, but they lack tactile and proprioceptive senses. Different approaches have been studied to implement sensory feedback in these devices. Sensory substitution is a method for implementing sensory feedback noninvasively. In this method, a different sense (or sensory organ) is used to deliver sensory information related to a lost sense (or sensory organ). In this paper, we proposed to provide proprioceptive information to users through probes sliding on skin. The device, which is attached on the forearm, has three probes representing thumb, index and the remaining fingers. The probes are moved by linear servo motors. Six subjects were tested to differentiate six hand postures based on the information from the device. Their performance was significantly higher than the chance level. Also, there was no statistically significant systematical errors in differentiating hand postures. Therefore, the device is promising for providing proprioceptive feedback in prostheses. © 2020 Turkish Chambers of Electrical Engineers.Öğe Reconstructive sensing circuit for complementary resistive switches-based crossbar memories(Tubitak Scientific & Technical Research Council Turkey, 2016) Karakulak, Ertuğrul; Mutlu, Reşat; Uçar, ErdemComplementary resistive switches (CRSs) are suggested as an alternative to one-cell memristor memories to decrease leakage currents. However, their sensing is more difficult and complex than one-cell memristor memories. A method has been given for sensing their state using only DC voltages in the literature. However, in this strategy, sensing one of the logic states results in the destruction of the state and the destroyed state must be written again. To the best of our knowledge, a circuit with this sensing strategy does not exist in the literature yet. In this paper, such a circuit employing this method, which is able to read the CRS cells and able to reconstruct their data if the data are destroyed, is given. A new CRS model is also constructed in this paper and used for simulations to verify the operation of the circuit. The circuit is simulated using Simulink. We expect this circuit implementation to find use in the design and testing of CRS cells.Öğe Sneak path current equivalent circuits and reading margin analysis of complementary resistive switches based 3D stacking crossbar memories(Soc Microelectronics, Electron Components Materials-Midem, 2014) Karakulak, Ertuğrul; Mutlu, Reşat; Uçar, ErdemSneak path currents of resistive memories is an important issue. They increase with increasing memory size and should be minimized for a usable resistive memory. The complementary resistive cells have been suggested as an alternative to one-cell resistive memories to decrease leakage currents. In literature, multilayer resistive memory topologies have also been inspected to minimize leakage currents. Recently, feasibility of 3D resistive RAMs is also inspected. However, to the best of our knowledge, no one has given equivalent leakage circuit models for complementary resistive switches based 3D resistive RAMs yet. In this study, equivalent leakage circuit models for different layers of a 3D resistive RAM with complementary resistive cells have been given and their leakage resistance and reading margins are compared to that of one layer crossbar memory. Some interesting and crucial results are obtained. Alternative complementary resistive switches based 3D resistive RAM topologies with insulating layer(s) for minimized leakage currents are suggested.Öğe SPICE Model of Current Polarity-Dependent Piecewise Linear Window Function for Memristors(2020) Karakulak, Ertuğrul; Mutlu, ReşatMemristor and memristive systems are nonlinear systems. It is important to model them accurately. There are different memristor models and most of the models make use of window functions. In literature, there are various window functions. Recently, a piecewise linear (PWL) window function is used to model a memristor and memristive systems. Such a memristor with a PWL window function lacks a SPICE model. Also, in literature, there is current polarity dependent window functions proposed for memristors to model polarity dependent drift speed within the thin-film memristors. In this study, an alternative current-polarity dependent PWL window function is suggested to model a memristor, a different PWL function one for each current polarity is used, its SPICE model is made in LTSpice and also its simulation results are given. Such a model can be used to model the polarity dependent drift speed within the thin-film memristors.Öğe Spice model of current polarity-dependent piecewise linear window function for memristors(Gazi Universitesi, 2020) Karakulak, Ertuğrul; Mutlu, ReşatMemristor and memristive systems are nonlinear systems. It is important to model them accurately. There are different memristor models and most of the models make use of window functions. In literature, there are various window functions. Recently, a piecewise linear (PWL) window function is used to model a memristor and memristive systems. Such a memristor with a PWL window function lacks a SPICE model. Also, in literature, there is current polarity dependent window functions proposed for memristors to model polarity dependent drift speed within the thin-film memristors. In this study, an alternative current-polarity dependent PWL window function is suggested to model a memristor, a different PWL function one for each current polarity is used, its SPICE model is made in LTSpice and also its simulation results are given. Such a model can be used to model the polarity dependent drift speed within the thin-film memristors. © 2020, Gazi Universitesi. All rights reserved.Öğe STM32F429 Discovery Board-Based Emulator for Lotka-Volterra Equations(2021) Karakulak, Ertuğrul; Tan, Rabia Korkmaz; Mutlu, ReşatLotka-Volterra equations are commonly used in prey-predator population studies. Simulation programs are commonly used to produce solutions of Lotka-Volterra equations and to examine their initial value dependendence. In literature, chaotic waveform generators, ECG and EEG generators have been made and used for research and education. To the best of our knowledge, such an electrical circuit to produce the Lotka-Volterra waveforms does not exist. Such a circuit can be made using either analog or digital circuit components. However, such a device may be used for education in classroom and also to prove concepts by population researchers. In this study, implementation and experimental verification of the microcontroller-based circuit which solves Lotka Volterra equations in real time and produces its waveforms are presented. Euler method is used to solve the equation system in discrete time. Presented design has been implemented using an STM32F429 Discovery Board, two DACs and four opamps. The microcontroller sends the signals to the outputs of the circuit using digital-to-analog converters and opamps. The waveforms acquired experimentally from the implemented circuit outputs matches well with those obtained from numerical simulations.Öğe Ters-Paralel Bağlı Schottky Diyot Dizisi Tabanlı Van der Pol Osilatörü Devresinin Modellenmesi ve LTspice ve Simulink Kullanarak Analizi(2021) Mutlu, Reşat; Karakulak, Ertuğrul; Çakır, KübraVan der Pol Osilatörü 1926 yılında, Philips’te çalışan elektrik mühendisi ve fizikçi Dr. Balthasar Van der Pol tarafından keşfedilmiştir. Bu osilatör çeşidinin oldukça zengin dinamikleri mevcuttur. İlk yapılan Van der Pol Osilatörü’nde bir triyot kullanılmıştır. Günümüzde Van der Pol Osilatörü, farklı yarı iletken elemanları kullanılarak yapılabilmektedir. Bu çalışmada, nonlineer devre elemanı olarak Schottky diyotlar kullanılmıştır. Bir endüktör, bir kondansatör, ters-paralel bağlı Schottky diyot dizisi ve paralel bağlanmış negatif direnç devresinden oluşan bu yeni Van der Pol Osilatörü’nün devre denklemleri türetilmiş ve benzetimi yapılarak incelenmiştir. Benzetimlerde devrenin sınır döngüsü, devre elemanlarının akımları ve devrenin gerilimi LTspice devre analizi programı ve Matlab’in Simulink paket programı kullanılarak elde edilmiştir.Öğe The memristive system behavior of a diac(Springer, 2020) Karakulak, Ertuğrul; Mutlu, ReşatThe memristor was introduced as a nonlinear circuit element in 1971, and systems showing memristor-like properties such as zero-crossing hysteresis loops were described in 1976. In 2008, a thin-film system that behaved like a memristor over some part of its operating region was discovered. Memristors and memristive systems have thus become a hot research area in recent years, making it important to discover and study such systems that show memristive behavior. Memristors and memristive systems exhibit three distinguishing characteristics that are known as their three fingerprints. Discharge lamps were also shown to exhibit memristive behavior recently. The diac, an electronics component commonly used in alternating-current (AC) applications, exhibits a breakdown mechanism similar to that observed in discharge lamps. According to textbooks, a diac should also obey the characteristics of a memristive system. In this work, a phenomenological model for a diac is first presented, and it is shown that this model satisfies the description of a memristive system; circuit simulations are also used to verify the memristive system behavior of a diac. However, experiments performed on a DB32 diac reveal that it only behaves like a memristive system in a narrow frequency range around 1 kHz. The effect of the junction capacitances of the diac are found to be important in this regard, resulting in the deviation of the diac from the expected memristive system behavior, as supported by the model and circuit simulations. We also believe that the reverse recovery current at frequencies above 1 kHz inhibits the zero-crossing behavior of the diac, even though its hysteresis curve is very similar to that of a memristive system.Öğe Three Sliding Probes Placed on Forelimb Skin for Proprioceptive Feedback Differentially yet Complementarily Contribute to Hand Gesture Detection and Object-Size Discrimination(Springer, 2024) Devecioğlu, İsmail; Karakulak, ErtuğrulThe purpose was to assess the effectiveness of three sliding tactile probes placed on the forelimb skin to provide proprioceptive feedback for the detection of hand gestures and discrimination of object size. Tactile contactors representing the first three fingers were driven along the proximodistal axis by linear servo motors. Twenty healthy subjects were involved in the gesture detection test, with 10 of them also participating in the object-size discrimination task. Motors were controlled by computer in the first four sessions of the gesture detection experiment, while the fifth session utilized a sensorized glove. Both the volar and dorsal sides of the forearm were examined. In the object-size discrimination experiment, the method was exclusively assessed on the volar surface under four distinct feedback conditions, including all fingers and each finger separately. The psychophysical data were further analyzed using a structural equation model (SEM) to evaluate the specific contributions of each individual contactor. Subjects consistently outperformed the chance level in detecting gestures. Performance improved up to the third session, with better results obtained on the volar side. The performances were similar in the fourth and fifth sessions. The just noticeable difference for achieving a 75% discrimination accuracy was found to be 2.90 mm of movement on the skin. SEM analysis indicated that the contactor for the index finger had the lowest importance in gesture detection, while it played a more significant role in object-size discrimination. However, all fingers were found to be significant predictors of subjects' responses in both experiments, except for the thumb, which was deemed insignificant in object-size discrimination. The study highlights the importance of considering the partial contribution of each degree of freedom in a sensory feedback system, especially concerning the task, when designing such systems. © The Author(s) 2024.
