Solar Charge Controller (SCC) with Maximum Power Point Tracking (MPPT) is needed to extract maximum energy from photovoltaic. However, a SCC device with MPPT technology feature is expensive on the market due to the requirements for a high-power system. On the other hand, in lower power applications such as IoT sensors, solar street lights, and wireless communication nodes, these types of controllers can be produced at a lower cost. In this study, the design of a low-cost SCC was conducted using the MPPT technology for low-power solar applications. The SCC is designed based on the Arduino microcontroller, which has the role of controlling the circuit and producing PWM signals to regulate the DC-DC converter. Several tests were conducted to validate the efficiency of the MPPT algorithm. The SCC device succeeded in increasing efficiency up to 52% on the low irradiance level.

Hemoglobin (Hb), a protein found within red blood cells, is responsible for transporting oxygen and carbon dioxide gasses. A low concentration of Hb indicates the existence of anemia. Traditional invasive Hb examination methods are accurate but have drawbacks, such as pain. A new approach, non-invasive photoplethysmography (PPG), addresses these issues and allows real-time Hb examination. In this article, the dataset consists of PPG signal, gender, age, and Hb value. The PPG signal was measured by a MAX30102 module sensor that emitted two types of light (red and infra-red light) and measured using a photodetector. Total of 68 subjects (56% female and 44% male) within the age of 18–65 years were collected. The total dataset is 816 data from 68 subjects, which each subject provides 12 sets of red and infra-red light signals. The data were collected at Primary Health Center Jatiuwung, Tangerang City, Banten 15,138, Indonesia. Researchers interested in anemia monitoring and those pursuing the development of non-invasive hemoglobin measurement based on machine learning can leverage this dataset.

The production of graphene from cost-effective and readily available sources remains a significant challenge in materials science. This study investigates the potential of common pencil leads as precursors for graphene synthesis using the Flash Joule Heating (FJH) process. We examined 6H, 4B, and 14B pencil grades, representing different graphite-to-clay ratios, under varying voltages (0 V, 200 V, and 400 V) to elucidate the relationships among initial composition, applied voltage, and resulting graphene quality. Samples were characterized using Raman spectroscopy, electrical resistance measurements, and microscopic analysis. The results revealed grade-specific responses to applied voltages, with all samples showing decreased electrical resistance post-FJH treatment. Raman spectroscopy indicated significant structural changes, particularly in I_D/I_G and I_2D/I_G ratios, providing insights into defect density and layer stacking. Notably, the 14B pencil lead exhibited unique behavior at 400 V, with a decrease in the I_D/I_G ratio from 0.135 to 0.031 and an increase in crystallite size from 143 nm to 612 nm, suggesting potential in situ annealing effects. In contrast, harder grades (6H and 4B) showed increased defect density at higher voltages. This research contributes to the development of more efficient and environmentally friendly methods for graphene production, potentially opening new avenues for sustainable and scalable synthesis.

Ultrafine plasma jet is a promising technology with great potential for nano- or micro-scale surface modification. In this letter, we demonstrated the use of ultrafine atmospheric pressure plasma jet (APPJ) for patterning bio-immobilization on vertically aligned carbon nanotube (CNT) microarray platform without a physical mask. The biotin-avidin system was utilized to demonstrate localized biomolecule patterning on the biosensor devices. Using ±7.5 kV square-wave pulses, the optimum condition of plasma jet with He/NH₃ gas mixture and 2.5 s treatment period has been obtained to functionalize CNTs. The functionalized CNTs were covalently linked to biotin, bovine serum albumin (BSA), and avidin-(fluorescein isothiocyanate) FITC, sequentially. BSA was necessary as a blocking agent to protect the untreated CNTs from avidin adsorption. The localized patterning results have been evaluated from avidin-FITC fluorescence signals analyzed using a fluorescence microscope. The patterning of biomolecules on the CNT microarray platform using ultrafine APPJ provides a means for potential application of microarray biosensors based on CNTs.