In this paper is reported the development and validation of a Shield prototype for resistive sensor array characterization with Arduino UNO, a platform based on ...
Lecture Notes in Electrical Engineering, 268 (2014) 411-415 (doi: 10.1007/978-3-319-00684-0_79)
ARDUINO-BASED SHIELD FOR RESISTIVE GAS SENSOR ARRAY CHARACTERIZATION UNDER UV LIGHT EXPOSURE D. ALOISIO, N. DONATO, G. NERI Department of Electronic Engineering, Chemistry and Industrial Engineering, University of Messina, Contrada di Dio, 98166 Messina, Italy. M. LATINO Consiglio Nazionale Delle Ricerche, Istituto per la Microelettronica e Microsistemi, Zona Industriale VIII Strada 5, I-95121 Catania, Italy. T. WAGNER, M. TIEMANN Universität Paderborn, Naturwissenschaftliche Fakultät, Department Chemie, Warburger Straße 100, D-33098 Paderborn, Germany P. P. CAPRA Istituto Nazionale di Ricerca Metrologica, 1013 5 Torino, Italy In this paper is reported the development and validation of a Shield prototype for resistive sensor array characterization with Arduino UNO, a platform based on ATmega328 microcontroller provided by ATMEL. The resistance variation of the sensor can be evaluated by properly choosing the capacitance value and by measuring the period (frequency) of a custom inverter-based oscillator. The GUI and the developed firmware are able to perform the real time monitoring of the sensor responses. The developed shield is able to measure the response of up to six sensors under UV radiation by means of LED devices. As an example, tests carried out with resistive sensors based on mesoporous In2O3-based material under UV light are reported.
1. Introduction The development of nanostructured sensing material and their integration in microelectronics devices is the key for the actual increasing of sensors market. Nanostructured sensing materials optimization can be considered as the turning point for the development of devices able to achieve the right balance between low power consumption requirements and sensing performance. The low power consumption requirements can be fulfilled by developing sensing materials able to operate itself at conditions close to room temperature, or by UV “activation”. As an example of this concept, mesoporous In2O3-based material can be irradiated with UV light to enhance the sensing properties to decrease the operating temperature value [1]. Therefore, new applications and services are arising, supported by the improvement of new portable and low cost sensing systems. In such task, here is reported the development of a characterization system for Metal OXides (MOX) based gas sensors with Arduino UNO platform. The developed shield is able to measure the response of up to six sensors under UV radiation by means of LED devices. In the shield takes place the board with six inverterbased oscillators where the RC tank of every circuit is composed by the resistance of the sensor (R) and an external capacitance (C). By properly choosing the capacitance value and by measuring the period (frequency) of the oscillator, the resistance response of each sensor can be evaluated. 2. Experiments The mesoporous sensing material development and characterization were reported in previous papers [1,2]. Here are reported the experimental activities regarding the board for hardware interfacing. A good alternative to realize real time resistance measurements is to use an oscillator system whose frequency is resistance value dependent [3]. This approach avoid use of A/D converters and simplify the interfacing circuit of the sensor. The measurement system core is based on an oscillator circuit in which frequency depends on the resistor value presents in the RC thank of the resonant ring. It’s
based on two inverter gate and a Schmidt trigger, essential for a proper RC charge and discharge, all connected in a loop for triple inversion of feedback signal. In this configuration choosing proper capacitance value is possible to adjust the range of measurement, see block diagram in Figure 1. The single sensor cell was then replicated to handle an array configuration by developing a sensor shield for Arduino environment, fully compatible and able to be assembled with other ones in a modular structure (see Figure 2).
Figure 1.Measurement system scheme.
The frequency/period measurement is performed with an Arduino UNO platform. This choice is justified by a series of factors as low cost of the system, possibility to change firmware on-fly and overall great flexibility of the platform to control more than one sensor and/or other systems. The peripherals of atmega328, mounted over this board, ensure to control contemporary up to six sensor and UV exposition of the sample using UV LEDs. The frequency range is a balance related to the number of the sensors to characterize. For a single sensor, a wider frequency range can be achieved spanning from 1kHz to 5MHz.
(a)
(b)
Figure 2. (a) Shield Top and Bottom Layers, (b) assembled shields.
Arduino board, programmed with a proper developed library, provides both to read the frequency, by using internal interrupt events, and to send data by means of serial port on an external PC. The GUI, developed in Matlab Environment, is able to control the communication protocol, the measurement procedures and the LEDs Switching. Two libraries were used to realize the measure: the first one, for one channel use, with a greater range and the second one for multichannel use. Figure 3 reports the calibration diagram, obtained by comparing the measurement data of commercial resistive samples measured both with Agilent 34401 multimeter and the developed system respectively.
Resistance(Ω)
107 106 105 Rsample(measured with 34401A) RARDUINO(measured with Shield)
104 103 100
1000
10000
100000
1000000
F(Hz) Figure 3. Calibration diagram
3. Results Gas sensing tests were carried out inside a Teflon chamber equipped with 400 nm UV LEDs under controlled atmosphere. Mass flow controllers were used to adjust desired concentrations of target gas in dry air. The sensors were tested on a concentration range of NO2 spanning from 0.3 to 5 ppm. The experimental data show how the UV radiation can influence the resistance value. In Figure 4(a) is reported the resistive behavior of a mesoporous In2O3-based sensor exposed in dry nitrogen atmosphere and dark/UV light conditions. It can be seen how in presence of UV irradiation the resistance suddenly decreases, then when the UV light is turned off, the resistance value slowly increases.
(a)
LED ON
(b)
UV ON
10
In2O3_mes Ref: N2 RT
5
10
LED OFF
In2O3_mes Ref:20%O2/N2 RT
R/R0
Resistance(Ω)
106
1
104
0
1000
2000
3000
Time (sec)
4000
5000
0
1
2
3
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5
NO2 (ppm)
Figure 4. (a) Sample resistance under dry nitrogen and dark/radiation conditions, (b) calibration curve towards NO2 under UV irradiation at room temperature.
Figure 4(b) reports the response of the sensor towards NO2 at room temperature (RT) and under UV irradiation. The good response obtained is promising for use the sensor device developed in low power sensing applications.
4. Conclusions Here is reported about the development of an Arduino Shield for the characterization of resistive sensors. The shield is able to handle up to six sensors and six LEDs for UV irradiation. The system was calibrated and then validated in the characterization of mesoporous In2O3 sensing films towards NO2 as target gas. Further investigations are in progress in order to characterize several sensing materials and to improve the shield by integrating a temperature monitor/control for the sensing devices.
References [1]
[2]
[3]
T. Wagner, C.-D. Kohl, S. Morandi, C. Malagú, N. Donato, M. Latino, G. Neri, M. Tiemann, Photoreduction of mesoporous In2O3: Mechanistic model and utility in gas sensing, Chemistry - A European Journal,V. 18, Iss. 26, 25 June 2012, pp. 8216-8223. T. Wagner, C.-D. Kohl, C. Malagù, N. Donato, M. Latino, G. Neri, M. Tiemann, UV light-enhanced NO2 sensing by mesoporous In2O3: Interpretation of results by a new sensing model, Sensors and Actuators B, (in press), http://dx.doi.org/10.1016/j.snb.2013.02.025. J. L. Merino, S. A. Bota, R. Casanova, A. Diéguez, C. Cané, J. Samitier, “A Reusable Smart Interface for Gas Sensor Resistance Measurement”, IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, vol. 53, no. 4, 2004.
