Low-cost Interface Circuit Research Articles

An Efficient Interface Circuit for Lossy Capacitive Sensors

This paper presents a low-cost interface circuit for lossy capacitive sensors. Most of the capacitive sensors are lossy in nature, where the resistance value of the sensor significantly varies along with the capacitance value. Accurate measurement of those values of a lossy capacitive sensor is a challenging task. This paper deals with the development of an electronic interface circuit for such a capacitive sensor. The circuit is based on the measurement of quadrature and in-phase components of the signal. To extract the actual value of the capacitance and the resistance, an average of the quadrature and the in-phase components of output is required. This is implemented using a microcontroller and provides flexibility in averaging (e.g., adjustable length of data to be processed). A PCB of the circuit has been fabricated and tested in the laboratory using capacitors and resistors with known values. The accuracy of the circuit was better than 0.6% and −2.2% for the measurement of capacitance and resistance, respectively. Also, the circuit is highly linear (FS nonlinearity of 0.32%) for a wide range of capacitance measurement (162 pF–3.680 nF). To confirm the effectiveness of the circuit, it was interfaced to a lossy capacitive humidity sensor and another capacitive transducer to measure the dielectric constants of edible oils. The results were compared with a precision impedance analyzer (Agilent 4294A); the maximum relative error was noted as ±1.6% in the measurement of permittivity values of edible oil. The prototype developed has the option to easily adjust the sensitivity and operating range, depending on the application.

Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.

Flexible and Low-cost Interface Circuit for Electrochemical and Resistive Gas Sensors

This work presents a low-cost interface circuit for both electrochemical and semiconductor sensors for gas detection. The proposed circuit offers a high sampling rate, on the order of 25 ms, allowing the monitoring of the sensor behaviour even in presence of fast transients. The front-end has a single-voltage 3.3 V power supply and a time-coded digital signal output, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process. Possible integration in a single-chip solution, together with the digital electronics is furthermore facilitated. Experimental results, conducted on a discrete component prototype and with sample resistors to emulate the sensor, have shown a maximum linearity error in the estimation of the sensor current or resistance of about 5% over a measurement range of seven decades, demonstrating the validity of the proposed solution. The power dissipation of the front-end is less than 30 mW (at 3.3 V) and the front-end cost less than 10 EUR, making it suitable for the employment in low-cost and low-power gas detection systems.

A Low-Cost Interface Circuit to Enable A/D Conversion Using the Parallel Port

A simple and low-cost acquisition device using the computer parallel port has been used to implement a full acquisition system composed of an analogue interface, a 12-bit analogue-to-digital converter, a quad three to one multiplexer and a software package aimed at managing the acquisition process. The features of this system make its implementation a suitable educational resource for undergraduate students from Engineering, Physics and Computer Sciences faculties.

Low Cost Multidigit Hexadecimal Display for Microprocessors

In using microprocessors for monitoring and control purposes, it is often required to provide a multidigit hexadecimal display to show the measured variable from time to time. Display of hexadecimal numbers using the seven-segment displays is not easily possible without additional hardware/special-purpose integrated circuits. Alternatively, the same microprocessor can be used to scan the display segments accordingly, as in calculators. However, during the time spent in scanning the display, the microprocessor can not do any other job. Methods using hardware for multidigit displays (Hex.), are quite involved. In this paper, a low-cost interface circuit for an 8-digit (4-byte) display which can be extended easily for more bytes as well, is described.