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.

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 2 to 10 and temperature from 0 to 90 o C The

accuracy of pH and temperature was estimated about ±0.1 and ±0.32 o C,

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

multi-parameters of water in real time.

Keywords: pH; Temperature; Internet of Thing; Drinking water; GPRS

1 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 on-line 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-Máñez reported a multi-sensor 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

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 8 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

2 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 8 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

Figure 1 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

system is shown in Figure 1 The program of this system was written and compiled

by Atmel Studio 6 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 1 Approximate system’s component costs

Kit AVR V4 including Atmega 16 25

2.2 System’s architecture and algorithms

Figure 2 (a) Architecture and (b) block diagram of fabricated system

Architecture and block diagram of this system is shown in Figure 2 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

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 0 (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 3 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 1 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 3 System’s algorithms

3 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,

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 4 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]

Figure 4 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:

E E o 2.3RTloga i

nF

Where: E is total potential (in millivolts) between the glass electrode and reference electrode (Ag/AgCl); E o 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 a is the reaction quotient In the case i

of the hydrogen ion in solution, equation 1 represents as following:

1.98 10

o

Where: pH is defined as the negative logarithm of the hydrogen ion activity

Equation 2 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

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–to-Digital 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 (V o ) 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 V o 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 V o versus pH, the following equation is used by

the Atmega 16 to convert the value of V o to pH:

where S v =10.07 pH/V Furthermore, in order to correct the obtained pH value

S v is compensated for sample’s temperature as following [11]:

273.15

273.15

cal

vT vcal

T

T



where S vT is compensated slope at T degree of sample, S vcal is slope at calibrated

temperature (T cal)

Figure 5 (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 2 The error of pH measurement

of the fabricated system is estimated about ± 0.07 pH

Table 2 Measured pH value of some standard buffer solutions

(b) (a)

4.01 3.96 0.05

Furthermore, stability of pH measurement was determined and shown in Figure

6 (a) In these measurements, the buffer solutions with pH of 4, 7 and 10 were used

to measure for about 1 hour and each measurement was performed after 1 min 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 5 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 4 and 5, the T0s were higher than 40 oC and values of pH were out of standard range In the case of T0<40 oC and pH in the standard range from 6.5 to 8.5, the warning SMS message was not sent These obtained results confirmed that the warning SMS message function of the fabricated system was well operated as system’s algorithms (Figure 3)

Figure 6 (a) Stability of pH measurements,

and (b) warning SMS message function

Case 1 Case 2

Case 3 Case 4 Case 5

The fabricated system was used to on-line measure the temperature and pH of

tap water at 334 Nguyen Trai – Thanh Xuan – Hanoi Then the measured data were

successfully uploaded to thingspeak.com (Channel ID: 318914) from Oct 7 to Nov

1 through GPRS service using Module SIM800C (Figure 7) The temperature of

tap water was in the range from 24.45 to 27.91 oC, and its pH was from 7.42 to

7.97 Especially, the lowest temperature was 24.45 oC on Oct 19 corresponding to

the cool day in Hanoi; and the lowest pH was 7.42 on Oct 13 due to heavy rain for

a week before Therefore, these obtained data are reliable and accuracy In

conclusion, the on-line measurement function of the fabricated system was

successfully operated

3.2 On-line measurements

Figure 7 Online measured data of tap water uploaded to thingspeak.com

4 CONCLUSION

In this article, an online low-cost monitoring and warning system for pH and

temperature of water was designed and fabricated The obtained data indicated that

this system is stable and reliable for long time measurements The pH and

temperature of tap water was successfully online measured with accuracy of ±0.1

pH and ±0.32oC, respectively The measured data were successfully uploaded to

thingspeak.com through GPRS service based on Module SIM800C (Channel ID:

318914) Especially, when anomalies are detected, a warning SMS message is sent

to a selected mobile number indicating what is abnormal; this function is very

useful for manager of system Because of its low-cost, stability, good accuracy,

on-line measurements and attractive function of warning SMS message, this system is

suitable for water consumers, water companies and authorities

Acknowledgement: This research is funded by the Vietnam National

University, Hanoi (VNU) under project number QG.15 11

REFERENCES

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2(2005), pp 589-595

[3] Serge Zhuiykov, David O'Brien, and Michael Best, "Water quality assessment

by an integrated multi-sensor based on semiconductor RuO2 nanostructures",

Measurement Science and Technology, Vol 20, No 9(2009), pp 095201

[4] Serge Zhuiykov, "Solid-state sensors monitoring parameters of water quality for the next generation of wireless sensor networks", Sensors and Actuators B:

Chemical, Vol 161, No 1(2012), pp 1-20

[5] Haijiang Tai, et al., "Design and characterization of a smart turbidity transducer for distributed measurement system", Sensors and Actuators A:

Physical, Vol 175, No (2012), pp 1-8

[6] Ruan Yue and Tang Ying, "A Novel Water Quality Monitoring System Based

on Solar Power Supply & Wireless Sensor Network", Procedia Environmental

Sciences, Vol 12, Part A, No 0(2012), pp 265-272

[7] G C Anzalone, A G Glover, and J M Pearce, "Open-source colorimeter",

Sensors (Basel), Vol 13, No 4(2013), pp 5338-5346

[8] M Integrated, "Datasheet of DS18B20-Programmable Resolution 1-Wire

Digital Thermometer ", Avaiable from:

https://

www.maximintegrated.com/en/products/analog/sensors-and-sensor-interface/DS18B20.html

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chlorine, and temperature sensors", Sensors and Actuators B: Chemical, Vol

255, No (2018), pp 781-790

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LIT2007, 2013

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TÓM TẮT

NGHIÊN CỨU CHẾ TẠO HỆ ĐO ONLINE GIÁ THÀNH THẤP

CÓ KHẢ NĂNG THU THẬP VÀ CẢNH BÁO THÔNG SỐ NHIỆT ĐỘ VÀ pH CỦA NƯỚC

Trong nghiên cứu này, một hệ thống giá thành thấp có khả năng thu thập

online và cảnh báo thông số pH và nhiệt độ của nước được thiết kế và chế

tạo Hệ thống được xây dựng dựa trên vi xử lý giá thành thấp 8 bit Atmega 16

và hệ cảm biến cho nhiệm vụ thu thập thông số online và đánh giá kết quả đo

Hệ thống phù hợp để đo pH trong khoảng từ 2 đến 10 và nhiệt độ từ 0 đến

90 o C của nước Sai số của phép đo pH và nhiệt độ lần lượt là ±0.1pH và

±0.32 o C Các kết quả sau khi đo được gửi lên trang web thingspeak.com sử

dụng mạng di động không dây GPRS theo thời gian thực Đặc biệt, nếu một

trong các thông số đo đạc vượt chuẩn (QCVN 01:2009/BYT), hệ thống sẽ gửi

tin nhắn cảnh báo tới một số điện thoại xác định Các kết quả thu được cho

thấy hệ ổn định trong thời gian dài và có độ chính xác cao Do giá thành

thấp, độ chính xác cao, có khả năng đo online theo thời gian thực, hệ thống

này phù hợp cho mục đích đo đa thông số môi trường nước trong tương lai

Từ khóa: pH, Nhiệt độ, Internet kết nối vạn vật (IoT), Nước, GPRS

Author affiliations:

Faculty of Physics, Natural University of Science, Vietnam National University

*Corresponding author: phamvanthanh@hus.edu.vn