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    Conformable fractional-order derivative based adaptive FitzHugh-Nagumo neuron model
    (Slovak Univ Technology, 2023) Karakulak, Ertugrul
    Various neuron models have been proposed and are extensively examined in the scientific literature. The FitzHugh-Nagumo neuron model is one of the most well-known and studied models. The FitzHugh-Nagumo model is not biologically consistent but operationally simple. A fractional-order derivative is described as a derivative with a non-integer order. Caputo, Grunwald-Letnikov, and Riemann-Liouville are some of the well-known fractional order derivatives. However, a simple fractional-order derivative called the conformable fractional-order derivative has been proposed in the literature and it is much simpler to use. In literature, there are already neuron models with fractional-order derivatives. In this study, a FitzHugh-Nagumo model circuit with a conformable fractional derivative capacitor and conformable fractional derivative inductor is proposed. The proposed circuit is modelled, and its simulation results are given. The simulation results reveal that the model circuit shows both slow and fast adaptation in firing frequency under sustained current stimulation.
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    A Microcontroller-Controlled Optocoupler-Based Memristor Emulator and Its Usage in a Low-Pass Filter
    (Springer Int Publ Ag, 2024) Arapi, Mendi; Karakulak, Ertugrul; Mutlu, Resat
    A nonlinear circuit element called a memristor has become a popular research area today. Circuits that mimic the behavior of a memristor are called memristor emulators. There are many different types of memristor emulators made. There are also optoelectronic memristor emulators in the literature, albeit in small numbers. In this study, a microcontroller-controlled memristor emulator with a hand-made optocoupler was designed. The circuit is made using an inexpensive microcontroller, the STM32F103RB microcontroller. The emulator made was used in the design of an LP filter with an adjustable cutoff frequency of low and high pass. The operation of the emulator and the filter has been studied experimentally. Experimental results show that the emulator and the LP filter circuits perform well.
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    Providing Hand Posture Information via a 3-DoF Tactile Sensory Substitution System
    (IEEE, 2020) Karakulak, Ertugrul; Devecioglu, Ismail
    Motorized 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.
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    Sawtooth Signal Generator Using a Carbon-Based Memristor
    (Gazi Univ, 2024) Karakulak, Ertugrul; Mutlu, Resat
    It is possible to use the new electronic circuit element memristor in analog applications. Memristors or memristor emulators have already been applied in analog applications such as amplifiers, filters, oscillators, and chaotic circuits. In literature, it has been recently demonstrated that a memristor-based sawtooth signal generator can be built utilizing a memristor emulator and simulations with various memristor models. Such a sawtooth signal generator needs experimental verification with a memristor. Self-Directed Channel (SDC) Carbon-based Memristors are in the market now. Once, the memristor technology is mature enough, its applications may also follow soon. Any memristor application should be realized with a memristor, not an emulator. Knowm memristor has not been used to design a sawtooth signal generator in the literature previously. The aim of the study is to show that a sawtooth signal generator can be made using a Self-Directed Channel (SDC) Carbon-based Memristor and to examine it experimentally. The performance of this sawtooth signal generator is evaluated. The waveforms of the proposed circuit are also examined by varying its operating frequency. The simulation and experimental results are compared. It has been found that its waveforms can be predicted well up to 350 kHz and its high- frequency behavior is not predicted well above 350 kHz by the memristor model used.
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    Simple Synthetic ECG Generation via PWM Output of Microcontroller
    (Institute of Electrical and Electronics Engineers Inc., 2021) Usta, Beyza Nur; Tepeyurt, Berranur; Karakulak, Ertugrul
    Bio-potential signal generators are widely used for education, testing of devices and scientific purposes. Due to their high prices, these generators cannot be supplied in sufficient numbers. In this study, an ECG generator that generates a simple synthetic ECG and is inexpensive is proposed. The generator obtains the ECG signal with a simple ECG model and the internal Pulse Width Modulation (PWM) port of the microcontroller is used to obtain the analog signal. In this way, an ECG signal generator can be obtained with less electronic material. The circuit is built and the experimental results of the circuit are given. © 2021 IEEE.