Design and fabrication of an online low cost monitoring and warning system for temperature and pH of water

In this study, an online low-cost monitoring and warning system for pH and temperature of water is presented with the design and construction described in detail. This system was constructed based on the low cost 8-bit Microcontroller Atmega 16 and sensor node for real time monitoring.

Research DESIGN AND FABRICATION OF AN ONLINE LOW-COST MONITORING AND WARNING SYSTEM FOR TEMPERATURE AND pH OF WATER Pham Van Thanh*, Nguyen Tien Dat, Dang Xuan Bai, Nguyen Thi Phong, Vi Van Hoang Abstract: In this study, an online low-cost monitoring and warning system for pH and temperature of water is presented with the design and construction described in detail This system was constructed based on the low cost 8-bit Microcontroller Atmega 16 and sensor node for real time monitoring The pH and temperature of water were measured in-pipe and on-line This system is suitable to measure pH in the range from to 10 and temperature from to 90 oC The accuracy of pH and temperature was estimated about ±0.1 and ±0.32 oC, respectively These measured parameters were successfully uploaded to thingspeak.com through GPRS service in real time Specially, these parameters were automatically evaluated based on QCVN 01:2009/BYT standard for tap water If one of measured parameters was out of standard ranges, a warning SMS message was sent to the selected mobile number The obtained results showed that the fabricated system is stable for longtime with reliable results Because of low-cost, good accuracy and on-line measurement, this system is suitable for monitoring multiparameters of water in real time Keywords: pH; Temperature; Internet of Thing; Drinking water; GPRS INTRODUCTION Clean drinking water is very important for the health of all humans However, drinking water have many challenges because of limited resources, growing population, industrial activities, attention of safeguarding water supplies from accidental or deliberate contamination [1] Therefore, it is needed to have an online water monitoring systems to detect contaminations and quickly evaluate the drinking water quality in real time To evaluate the quality water, many multi-parametric sensor arrays and water quality monitoring systems have been developed and reported in previous articles Lambrou suggested some main parameters of drinking water which are suitable for real time monitoring including temperature, turbidity, oxidation reduction potential (ORP), pH, and electrical conductivity (EC) [1] Martínez-Máđez reported a multisensor based on thick-film technology to control the water quality; especially, a stationary unit for water quality monitoring was successfully constructed by using Analog Data Acquisition Card Adlink PCI 9112 connected to personal computer [2] An integrated multi-sensor based on semiconductor RuO2 nanostructures for water quality assessment on temperature, pH, conductivity and turbidity was designed and fabricated by Serge Zhuiykov et al [3, 4] Haijiang Tai presented a smart turbidity transducer with temperature compensation for distributed measurement system [5] In addition, Ruan Yue reported a water quality Journal of Military Science and Technology, Special Issue, No.54A, 05 - 2018 27 Electronics & Automation monitoring system based on solar power supply and wireless sensor network in which the pH and turbidity of water were successfully measured in real time [6] Furthermore, a colorimeter was also implemented by Anzalone et al based on the open-source Arduino prototyping platform [7] These researches show that the smart and online monitoring system for assessment on the quality of water is very interesting and need to develop more in future However, these researches have not yet had automatic warning function if one of water’s parameters is out of standard which is very important for automatic on-line system In this report, we designed and constructed an on-line automatically monitoring and warning system for pH and temperature of water This system was fabricated based on a low-cost bit Microcontroller Atmega 16 The sensor node including pH and temperature sensors was developed based on Hanna HI-1110B and DS18B20 sensors, respectively Obtained data were successfully uploaded to thingspeak.com through GPRS service base on Module SIM800C Especially, when one of pH and temperature parameters is out of the standards for drinking water, a warning SMS message is sent to a selected mobile number EXPERIMENTS 2.1 Materials The Hanna HI-1110B combination electrode is used as pH sensor, in which the electrolyte is gel filled and Ag/AgCl electrode is reference electrode The digital temperature sensor DS18B20 (Maxim Integrated TM) is used to measure water’s temperature The casing of sensor node casing of sensor node is 21-mm diameter PVC tube (Tien Phong Plastic Joint-Stock company) The central processing of system is the low-cost bit Microcontroller Atmega 16 (Atmel Corporation) installed on KIT AVR V4 (Minh Ha Group) for developer The obtained parameters is uploaded to thingspeak.com through GPRS service based on the Module SIM800C, this module is also used to send a warning SMS message if any parameter of water is out of the standard range a) b) c) d) Figure Components of systems: (a) pH combination sensor Hanna HI-1110B, (b) temperature sensor DS18B20 in waterproof casing, (c) Kit AVR V4, and (d) Module SIM800C The FOX-2005 temperature meter is used as reference to evaluate accuracy of temperature measurement The Hanna pH buffer solutions with the pH variation of 4, 7, and 10 are used to calibrate the pH measurement All components of this 28 P V Thanh, …, V V Hoang, “Design and fabrication … temperature and pH of water.” Research system is shown in Figure The program of this system was written and compiled by Atmel Studio The approximate cost of system’s components is shown in Table 1; it is shown that the total cost of system is about 120.5$ at the time of manufacture Table Approximate system’s component costs Components Approximate cost ($) Hanna HI-1110B 75 DS18B20 1.5 Kit AVR V4 including Atmega 16 25 LCD 16x2 Module SIM800C 10.5 21-mm diameter PVC ~ 5.5 Total ~120.5 2.2 System’s architecture and algorithms a) b) Figure (a) Architecture and (b) block diagram of fabricated system Architecture and block diagram of this system is shown in Figure The sensor node includes pH sensor (Hanna HI-1110B) and temperature sensor (DS18B20) The casing of the sensor node was fabricated by the 21-mm diameter PVC pipe due to its stable, high chemical resistance and low-cost An electric valve is mounted on the PVC pipe to control time of water flow by PA2 pad of Atmega 16 In this system, the DS18B20 sensor communicates with Atmega 16 over a 1-Wire Journal of Military Science and Technology, Special Issue, No.54A, 05 - 2018 29 Electronics & Automation bus through PA0 pad of Atmega 16 While the output potential of pH sensor was amplified and then connected to Analog-to-Digital-Converter channel (ADC0) of Atmega 16, the 10 bit resolution of this ADC0 was selected with internal reference voltage of 2.56V The Module SIM800C communicated serially with Atmega 16 by UART protocol Furthermore, the measured parameters were also displayed on the Liquid Crystal Display (LCD) Figure shows the algorithms of this fabricated system Firstly, the system is started and resets all parameters of system Then Atmega 16 opens the electric valve for minute Next step, the system measures data and displays them on the LCD each second After 60 seconds, the system measures and selects the temperature of water which would be used to evaluate at end of program After 300 s, the system measured and selected the pH of water And then, the system automatically evaluated the temperature and pH based on QCVN 01:2009/BYT standards for water If temperature is higher than 40 oC (T0) or pH is out of range from 6.5 (pH1) to 8.5 (pH2), a warning SMS message would be sent to a selected mobile number Finally, all logged data are uploaded to thingspeak.com using GPRS service based on the Module SIM800C Figure System’s algorithms RESULTS AND DISCUSSIONS 3.1 System calibrations The advantage of the DS18B20 is direct-to-digital to digital temperature sensor, the resolution of this temperature sensor is user-configurable to 9, 10, 11, or 12 bits, 30 P V Thanh, …, V V Hoang, “Design and fabrication … temperature and pH of water.” Research corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively [8] In this fabricated system, the 10 bits resolution of this sensor was selected To calibrate and evaluate the accuracy of this sensor, the increasing and decreasing temperature processes of water were carried out, the water’s temperature was measured by both of the fabricated temperature system and the FOX 2005 temperature controller as reference with resolution of 0.01oC The increasing temperature process was performed by natural warming of ice-water from 0oC to 25oC, and the decreasing one was done by natural cooling of hot water from 90oC down to 25oC The obtained temperatures shown in Figure For both processes, the water’s temperatures measured by DS18B20 sensor are very close to one of the FOX2005, the average errors of the fabricated system were calculated to be 0.32oC and 0.22oC for the increasing and decreasing processes, respectively These results indicated that this DS18B20 is comparable with other systems reported by Lambrou et al [1] and Yiheng Qin et al [9] (a) (b) Figure The water’s temperature of (a) increasing temperature process and (b) the decreasing one measured by DS18B20 and FOX 2005 The Hanna HI-1110B is glass combination pH sensor that converts pH of water to output potential based on Nernst equation [10] as following: 2.3RT E  Eo  log (1) nF Where: E is total potential (in millivolts) between the glass electrode and reference electrode (Ag/AgCl); Eo is the standard potential of the ion; R is the gas constant (8.314 Jmol-1K-1); T is the temperature; F is Faraday’s constant, which is 9.6437 ×104 J V-1mol-1; n is charge of the ion; and is the reaction quotient In the case of the hydrogen ion in solution, equation represents as following: E  E o  1.98  104   T  pH (2) Where: pH is defined as the negative logarithm of the hydrogen ion activity Equation shows that the value of E is linear dependence on pH of solution The slope of this dependence will change when temperature changes Therefore, the Journal of Military Science and Technology, Special Issue, No.54A, 05 - 2018 31 Electronics & Automation temperature compensation to slope of this dependence is needed to improve the accuracy of pH measurement Notably, due to the high resistance of about 100 MΩ, the output potential of the Hanna HI-1110B pH sensor is needed to amplify before applying it to Analog–toDigital Converter (ADC) and then logging by the Atmega 16 The pH amplifier was designed and fabricated based on TL082 op-amp The schematic circuit of this amplifier is shown in Figure 5(a) The output voltage (Vo) of this pH amplifier was calibrated at room temperature (~25 oC) by the standard buffer solutions with pH variation of 4, 7, and 10 The linear dependence of Vo versus pH was obtained and shown in Figure 5(b) with R2=0.9995 The slope (s) of this linear dependence was estimated to be 99.3 mV/pH Based on linear dependence of Vo versus pH, the following equation is used by the Atmega 16 to convert the value of Vo to pH: pH  Sv  Vo  1.26 (3) where Sv=10.07 pH/V Furthermore, in order to correct the obtained pH value Sv is compensated for sample’s temperature as following [11]: T  273.15 S vT  S vcal  cal (4) T  273.15 where SvT is compensated slope at T degree of sample, Svcal is slope at calibrated temperature (Tcal) (a) (b) Figure (a) pH amplifier circuit and (b) Vo vs pH of buffer solution By using equation 4, the fabricated system was measured and displayed the pH values of some solutions which indicate as Table The error of pH measurement of the fabricated system is estimated about ± 0.07 pH Table Measured pH value of some standard buffer solutions pH of solution Measured pH Error 1.68 1.61 0.07 32 P V Thanh, …, V V Hoang, “Design and fabrication … temperature and pH of water.” Research 4.01 7.00 10.01 3.96 6.99 9.94 0.05 0.01 0.07 Furthermore, stability of pH measurement was determined and shown in Figure (a) In these measurements, the buffer solutions with pH of 4, and 10 were used to measure for about hour and each measurement was performed after It is indicated that the pH measurements is stable for long time with average variation being about ± 0.1 pH This obtained result is comparable to other on-line pH measurement system [1, 9, 12] Therefore, this system is suitable for on-line pH measurements of water The warning SMS message function of the fabricated system was also investigated and shown in Figure 6(b) The cases of warning messages were indicated In case 1, the sample’s temperature (T0) was shown normal meaning that T0 is smaller than standard temperature of 40oC, sample’s pH was 3.94 lower than one of standard range from 6.5 to 8.5 In case 2, the sample’s temperature (T0) was shown normal, while the sample’s pH was 9.85 higher than pH2=8.5 In case 3, sample’s pH was normal meaning that which is in range from 6.5 to 8.5; T0 is 70.56 oC higher than 40 oC In case and 5, the T0s were higher than 40 oC and values of pH were out of standard range In the case of T0