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Timer-Based Capacitance-to-Voltage Converter
(2026-03-01)
Kaewpoonsuk, Anucha
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Tokampang, Sudarat
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Sisuk, Noppadon
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Rerkratn, Apinai
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Petchmaneelumka, Wandee
This article presents the design and analysis of a capacitance-to-voltage converter based on 555-timer Integrated Circuits (ICs) as the core design element. The circuit structure consists of two primary active components: two 555-timer ICs connected in conjunction with a low-pass filter circuit. The first 555-timer IC operates in astable mode to generate a signal that controls the timing of the second IC. The target capacitor or capacitive sensor to be measured is connected to the second 555-timer IC, which operates in monostable mode. The output signal from the second 555-timer IC is then converted into a DC voltage output using a low-pass filter circuit. The circuit was tested using laboratory capacitors in the range of 52.72 pF to 807.61 pF, and the data were analyzed using Microsoft Excel. The results showed excellent agreement with the measurements obtained from the GW INSTEK LCR-819. The maximum uncalibrated error was found to be −3.32% of full scale. After applying linear curve fitting in Excel, the maximum error was reduced to 0.92% of full scale, confirming the effectiveness of the calibration approach. Furthermore, the circuit was applied to measure the moisture content of paddy rice using a cylindrical capacitive sensor within the moisture range of 12.1% to 23.2%. The experimental data were fitted to a derived equation, which was then used to predict rice moisture content, producing results that corresponded closely with those obtained from the KETT PM-450 grain moisture meter.
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DEVELOPMENT OF AN EMBEDDED EXERCISE POSTURE PREDICTION SYSTEM FOR OFFICE SYNDROME USING MACHINE LEARNING
(2024-12-01)
Sisuk, Noppadon
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Onkhong, Tada
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Kaewpoonsuk, Anucha
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Wardkein, Paramote
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Prompak, Kriangsak
Office syndrome is a condition with a high prevalence among people of working age and an upward tendency. In this study, a wearable device implant based on machine learning will be created for exercise of office syndrome. Developing a machine learning model that can distinguish 3 exercise postures for implantable devices was the objective of the study. The Edge Impulse online software was used for data collecting, preprocessing, training, and testing. After that, the model was successfully installed and tested on an Arduino Nano 33 BLE microcontroller. In addition to designing embedded systems, this work also developed applications through the App Inventor program for exercising properly. From testing the system, the model showed an average classification accuracy of 97.6% of exercise postures. The results of testing the embedded system in conjunction with the presented application on 10 subjects showed that the system was able to provide predictive accuracy for wrist exercises, shoulder exercises and stretch exercises with 95%, 97%, and 93%, respectively.
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Resistive-Sensor Interfacing Circuit for Remote Measurement Using CFOA
(2024-01-01)
Petchmaneelumka, Wandee
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Rerkratn, Apinai
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Tammaruckwattana, Sirichai
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Kaewpoonsuk, Anucha
An alternative approach to implementing an interfacing circuit for resistive sensor-based remote measurement is presented. The proposed technique uses a Current Feedback Operational Amplifier (CFOA) as an active building block to produce an output voltage linearly related to the resistance of the sensor. Moreover, the accuracy of the output voltage is improved by the enhancement of CFOA. In addition, the proposed circuit provides compensation for the effects of lead-wire resistance. The performance of the proposed technique is discussed in detail and confirmed by PSPICE program simulation and experimental implementation. The resistance decade box is used in the experiment. The maximum error on the output voltage of the experimental results is about 0.4234 %. The experimental results show that the proposed technique provides good performance.
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Real-time seafood quality monitoring system using interdigital sensor
(2020-01-01)
Kaewpoonsuk, Anucha
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Luangpol, Amata
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Prasitmeeboon, Pitcha
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Rerkratn, Apinai
Many studies showed that seafood consumption contains many health benefits. However, the spoilage of such products causes the vast economic loss each year. An effective monitoring and inspection system for quality is required during the storage of these products. Most existing methods for such inspection require laboratory tests. In this study, the interdigital sensor was developed and applied to inspect the spoilage of seafood. The sensor was designed to monitor the change of impedance during spoilage progression of seafood. The result revealed that impedance of liquid decreased overtime. This coincides with the fact that spoilage of seafood generates ammonium ion which causes decrease in the impedance of the liquid. The designed sensor was then merged with the proposed system which consists of a sine wave circuit, a voltage control current source circuit, an interdigital sensor, an amplifier circuit, a rectifier circuit, a low-pass filter circuit, a comparator circuit and a display circuit. These circuits adjusted the signals received from the sensor to be proper to the application. The experiment was designed to have conditions similar to the real-world situation of how seafood is stored. The experimental results showed that the proposed system effectively indicated the change of seafood quality.
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Internet-based conductivity measurement system with self-temperature compensation
(2019-07-01)
Katman, Ratchanoo
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Rerkratn, Apinai
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Kaewpoonsuk, Anucha
An Internet-based conductivity measurement system with self-temperature compensation is presented in the paper. In order to get a simple and portable measurement system, a readout circuit in analog part is designed using only two operational amplifiers (opamps) connected with basic electronic components and energized using single supply voltage. An excitation voltage generated by the AD9833 module is applied to a conductivity sensor. The measured output DC voltages are found to be directly proportional to the conductivity of the solution. The NodeMCU ESP8266 WiFi dev board is used to determine the conductivity and measure the temperature whose effect on the conductivity is compensated. The measured results are sent to display on a smartphone by Blynk app. The conductivity measured by the proposed system is in good agreement with that due to the standard EC meter. A maximum error of measuring the conductivity at different temperatures of solution is 4.79% of full scale.
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OP-AMP based interface circuit for resistive sensor with lead-wire-resistance compensation
(2019-04-01)
Kaewpoonsuk, Anucha
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Katman, Ratchanoo
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Rerkratn, Apinai
This paper presents a simple technique to implement the resistive sensor interface for remote measuring. The circuit is designed using a relaxation oscillator to generate a square wave signal. The time difference during charging and discharging a capacitor is directly proportional to the sensor’s resistance. The structure of the circuit is composed of two op-amps, three bipolar junction transistors, a capacitor, four fixed resistors and a variable resistor. Features of the proposed circuit are single-supply operation and direct interface with a microcontroller without an analog-to-digital converter. In addition, the lead-wire resistance is automatically compensated. When the resistance values of the sensor are varied in the range of 500-1500 O with lead-wire resistance values of 0-100 ω, the result of the circuit testing is found that the maximum error is approximately equal to 1.15% of full scale. The performance of the circuit is in accordance with principles proposed.
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Simple and low-cost readout circuit for differential resistive sensors
(2018-09-01)
Katman, Ratchanoo
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Rerkratn, Apinai
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Kaewpoonsuk, Anucha
In this paper, a simple and low-cost readout circuit for differential resistive sensors is presented. The realization method is based on the relaxation oscillation technique, which utilizes the operational amplifiers (op-amps) with a single supply voltage. The oscillating output Duty-Cycle is proportional to the difference of two sensing resistances. In comparison with the traditional voltage divider circuit or the Wheatstone bridge circuit or the previously reported readout circuit based on CCIIs, the proposed circuit can be interfaced with microcontroller without using an analog-to-digital converter. Theoretical predictions are supported by the PSPICE simulation results and the experimental data. In applying a slide potentiometer with changes of slider positions of ±15 mm, it is found that the maximum error of the proposed circuit is approximately-2.90% of full-scale. Copyright © 2018 Praise Worthy Prize S.r.l.-All rights reserved.
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Analysis of beat frequency detector based on basic logic gates
(2018-08-01)
Kaewpoonsuk, Anucha
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Sisuk, Noppadon
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Smerpitak, Krit
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Wardkein, Paramote
The aim of this paper is to introduce a simple technique to analyze the operation of the basic logic gates-based beat frequency detector (BFD). We show that all of the basic logic gates, including AND-gate, NAND-gate, XOR-gate, XNOR-gate, OR-gate, and NOR-gate, can be used as a mixer to implement the BFD. This BFD is simple, easy to assemble, and can be used in control, instrument and measurement systems.
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Readout circuit for conductivity measurement with parasitic resistance compensation
(2018-08-01)
Katman, Ratchanoo
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Petchmaneelumka, Wandee
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Rerkratn, Apinai
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Kaewpoonsuk, Anucha
This paper presents a simple method based on commercially available current feedback operational amplifiers (CFOAs) to realize the readout circuit for measuring the solution conductivity including the parasitic resistance in the electrode sensor. The enhanced readout circuit for conductivity measurement in electrolyte solution, compared with the conventional readout circuit using the op-amp inverting amplifier, offers a technique for the parasitic resistance compensation to improve the linearity of the measurement results. The proposed readout circuit provides the digital output which is directly proportional to the conductivity of electrolyte solution. The experimental verification and the measured results of the method are included in this paper.
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Simple DC-excited resistance-to-period converter using CFOAS
(2018-05-01)
Kaewpoonsuk, Anucha
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Katman, Ratchanoo
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Rerkratn, Apinai
This paper presents a new method to implement a resistance-to-period converter for DC-excited resistive sensor. The proposed technique makes use of the characteristic of a controllable unity-gain inverting/non-inverting amplifier formed by current feedback operational amplifiers (CFOAs). Experimental results that verify the performance of the proposed circuit are also included.

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