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Development of a Phase-Locked Loop Circuit in Running Frequency Mode for Capacitance-to-Voltage Conversion
(2025-01-01)
On-Khong, Tada
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Sisuk, Noppadon
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Wardkein, Paramote
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Katman, Ratchanoo
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Prompak, Kriangsak
Capacitance-to-voltage conversion is essential for capacitive sensors in various industries, including touch interfaces, medical devices, and moisture measurement. However, circuit design faces challenges like non-linearity, noise, and small capacitance variations affecting voltage signals. This article proposes a phase-locked loop in free-running oscillator mode with a frequency-to-voltage converter to enhance accuracy and stability. Test results show a 97.9% measurement accuracy, demonstrating reduced noise and improved stability. The proposed circuit is ideal for high-precision applications in diverse environments, overcoming limitations of traditional methods.
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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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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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An amplitude detector using up-down counter
(2012-03-01)
Kaewpoonsuk, Anucha
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Katman, Ratchanoo
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Julsereewong, Amphawan
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Riewruja, Vanchai
This article presents a novel and simple amplitude detector for sinusoidal signals. The realization technique utilizes up/down counting and holding capabilities of up-down counter without low-pass filter or sample-and-hold circuit requirement. The proposed circuit consists of a control signal generator, a peak detector, a windows detector, a digital-to-analog converter, and an up-down counter. The proposed detector can produce both analog output and 12-bit digital output signals, which are proportional to the amplitude value of analog input signals. In addition, output signals with small ripple can be achieved. The experimental results show that the proposed detector can work with the input voltage in range 250 mV to 5 V. The maximum frequency for input signals is approximately equal to 100 kHz with maximum analog output error of 0.8%. © 2012 ICIC International.
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A simple amplitude detector-based demodulator for resolver converters
(2010-12-01)
Kaewpoonsuk, Anucha
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Katman, Ratchanoo
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Kamsri, Thawatchai
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Rerkratn, Apinai
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Riewruja, Vanchai
This paper presents a simple method based on sinusoidal-amplitude detector for realizing the resolver-signal demodulator. The proposed demodulator consists of two full-wave rectifiers, two ±unity-gain amplifiers, and two sinusoidal-amplitude detectors with control switches. Two output voltages are proportional to sine and cosine envelopes of resolver-shaft angle without low-pass filter. Experimental results demonstrating characteristic of the proposed circuit are included. ©ICROS.

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