an energy efficient microcontroller based digital solar weighing machine

2013 International Conference on Power, Energy and Control (ICPEC)

AN ENERGY EFFICIENT MICROCONTROLLER BASED DIGITAL SOLAR WEIGHING MACHINE S. Arisutha, Arvind Mittal and K. Sudhakar Energy Centre Maulana Azad National Institute of Technology Bhopal- 462 051, India e-mail: [email protected]

S. Suresh Department of Chemical Engineering Maulana Azad National Institute of Technology Bhopal- 462 051, India e-mail: [email protected]

D.M. Deshpande Department of Electrical Engineering Maulana Azad National Institute of Technology Bhopal Bhopal- 462 051, India Abstract— The main aim of this study is to develop a digital weighing machine and to operate it with the help of solar PV panel, where the supply of electricity is the biggest problem. This Study describes the design and implementation of a low-cost, energy efficient portable solar powered digital electronic weighing system ideal for domestic, laboratory and commercial use. The system has highly reduced circuitry as it utilizes a standalone microcontroller chip. As this machine not uses the electricity to charge, it saves the electrical energy. The system designed measures weights ranging from 0-30 kg.

It essentially comprises of an 8-bit 8051 microcontroller with a local memory module for storing data from the ADC. High resolution, without compromising range, is achieved by designing a program for interfacing a serial 10bit ADC to the 8-bit microcontroller [6]. This is due to the inbuilt Serial Programming Interface (SPI) of the microcontroller used. Fig. 1a-b shows the basic block

diagram and Photograph of the Setup

Keywords- weighingbalance solarpanel microcontroller

I.

INTRODUCTION

A digital weight machine measures weight by the distance a load cell deflects under its load. But here we are using solar cell as an electrical power input. Weighing scales are used in many industrial and commercial applications. In digital weighing machine the deflection of a beam supporting the unknown weight is measured using which is a lengthsensitive electrical resistance [1-2]. The capacity of such devices is only limited by the resistance of the beam to deflection. This work describes the design and implementation of a low-cost, high-resolution and portable digital electronic weighing system ideal for domestic, laboratory and commercial use. The system has highly reduced circuitry as it utilizes a standalone microcontroller chip [3-4]. The Developed electronic weighing balance senses, measures and displays the mass, placed on a single point load cell, on an LCD display. The results from several supporting locations may be added electronically, so this technique is suitable for determining the weight of very heavy objects, such as trucks and rail cars, and is used in a modern weighbridge [5]. II. DESCRIPTION OF THE EXPERIMENTAL SETUP:

(a)

(b) Figure 1. (a) Block Diagram and (b) Photograph of the digital weighing machine. The output of the load cell is given to the Instrument Amplifier IC - AD622, which amplifies the signal and passes the output to the microcontroller ATmega8L because the

978-1-4673-6030-2/13/$31.00 ©2013 IEEE 14

2013 International Conference on Power, Energy and Control (ICPEC) microcontroller cannot read the signal below 1 Volt and the load cell is giving the output in a few mV like 1.2mV, which is very small and weak signal so we need to amplify it. The Microcontroller is programmed with the help of CODE VISION AVR software and displays the output accordingly in the LCD display. (i)Load Cell: Load Cell is a device that converts force into electrical signal. A strain gauge based load cell is made of a specially engineered mechanical component called as an element. Four strain gauges are positioned precisely and bonded on to the element using a special adhesive [7]. Strain gauge is a device that changes resistance when it is deformed or stressed. Table 1shows the basic specifications of a load cell. The forceelectrical signal conversion happens in two stages(i) Force applied deforms the element which in turn deforms the strain gauges (ii)Strain gauges convert the deformation to electrical signals. Fig. 2 shows the circuit diagram of load cell

Figure 3. Internal Structure of Ad622 The gain of AD622 IC is determined by using the equation: G = 1 + (50.5 kΩ/Rg) Gain = 506 Where,G = Gain Rg = Resistance to be used for setting the gain A 100Ω Resistance is used to set the gain (iii) Microcontroller – ATmega8L: A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals [8]. A low power ATmega8L microcontroller is used in this work . It has two 8bit bi-directional I/O ports and one 7-bit bi-directional I/O port which also serves as the ADC. A pin diagram of AT mega8L is represented in Fig. 4.

Figure 2. Circuit diagram of Load Cell Table 1. Basic specifications of a load cell Capacity 45Kg Full scale Output 45*0.6 = 27mV Sensitivity 2.25 mV/V Excitation Voltage 9V or 12V DC Input resistance 409 Ω Output resistance 350Ω (ii) Amplifier IC AD622 The AD622 replaces two or three op amp instrumentation amplifier designs and offers good commonmode rejection, superior linearity, temperature stability, reliability, and board area consumption [8]. The low cost of the AD622 eliminates the need to design discrete instrumentation amplifiers to meet stringent cost targets. While providing a lower cost solution, it also provides performance and space improvements. The Internal diagram of AD622 is represented in Fig. 3. Basically internal structure of AD622 consists of an Instrumentation Amplifier circuit which can easily be obtained by connecting 3 OPAMP like LM741.

Figure 4. Pin diagram of AT Mega 8L. (iv) LCD Display: A LCD is a small low cost display. It is easy to interface with a micro-controller. Each module uses a 5x8 dot matrix for each character position [9]. It can display 224 different characters and symbols including a cursor. Each module also has a low power variable intensity LED backlight. Power consumption is typically 1mA, 5V DC power supply. 15

2013 International Conference on Power, Energy and Control (ICPEC) 0.08 0.07

RESULTS

The characteristics of the Load Cell were determined by studying the Output signal of Load Cell with various weights applied to the Load Cell. 12V DC supply is applied for the excitation of the Load Cell and the output is measured in mV with the help of multimeter. A plot between Load and output signal revealed that the output varies linearly with the load applied to the load cell. Fig 5 shows the variation of current and output voltagewith varies wieght ranging from 0-30 Kg. Fig. 6 shows the variation between load and power. The results shows that there is linear variation between load and power. Fig 7 shows the Comparison of V-I Characteristics of solar source & Conventional Sources. It is concluded that consumed by solar panel is less than conventional energy source. 0.07

4

Output (V)

3

0.05 0.04

2 0.03

Output

1

Current

Current (mA)

0.06

0.02 0.01 0

0 0

5

10

15

20

25

Current (mA)

III.

0.3

0.21

0.01 0 1

Power (VA)

0.07

[4] [5]

0 12.05

15.67

Weight (kg)

19.34

23.21

3.08

3.46

3.82

REFERENCES

0.04

8.15

2.65

Our thanks to MANIT for providing necessary facilities and to Ministry of Human Resource Development (MHRD), Government of India for financial support.

[2] [3]

0.09

4.27

2.21

ACKNOWLEDGMENT

0.15

0

1.89

Figure 7. V-I characteristics of solar and conventional source. IV. CONCLUSION The results of studies carried out for the design and development of low cost, Solar based automatic weighing Machine indicated that the equipment could be used as Laboratory weigher. Performance analysis indicated that there was no significant difference in mean value of measurements from set weights (10, 20, 30 Kilograms) and measured weights at the 95% probability level. Minimum average percentage error (< 0.2%) was observed for 10, 20 and 30 Kilograms weight measurements. The measurements revealed that weighing of product by Solar digital weigher is very precise. Solar digital Automatic weighing Machine can be used for weighing and dosing of any products up to 30 Kg.

[1]

0.11

0.05

1.43

Voltage (V)

0.18

0.1

0.04

0.02

0.25

0.15

0.05

0.03

Weight(kg)

0.2

Solar Source

30

Figure 5. Current and Voltage Variation for differentWeight.

0.25

Conventional Source

0.06

26.89

Figure 6. Power consumed by digital weighing Machine.

[6] [7] [8] [9]

A.S. Buwono, H. Akbar, W. Usino. PC Based Weight Scale System with Load Cell for Product Inspection In Proceedings of ICCET International Conference on Computer Engineering and Technology DOI: 10.1109/ICCET.2010.182 http://www.imeko.org/publications/tc3-2002/IMEKO-TC3-2002-24.pdf http://www.hiwin.com/pdf/lg/0809/HiwinLinearGuidewayCatalog_G99 TE13-0809.pdf M. Halimic, Balachandran, W& Enab, Y, Fuzzy logic estimator for dynamic weighing system. IEEE Explore 0-7803-3645-3/96. (1996). G. A. Gonzalez, and A. Herrador, M., The assessment of electronic balances for accuracy of mass measurements in the analytical laboratory. Accredited quality assurance 12, 21-29. (2007). M. Shimauchi. Udo, (2002). Feed shutter for automatic grain weigher, JP2000053101-2000-02-22. (2002) V.V Subbotin, K.Yu Klimychev, V. N. Ruchkin, V., & Khaimovich, M.M., Upgrade of Electric weighing cars. Glass and Ceramics 60, 129130. 27 (2003). Okada and Shimauchi Automatic grain weighing machine, JP2001165756-2001-06-22. (2001). M. Jafaripanah, Al-Hashimi, B.M. and White, N.M. Design consideration and implementation of analog adaptive filters for sensor response correction. In Proceedings of the ICEE, Iran. (2004).

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