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Design and Development of Digital Voltmeter Using Different Techniques1Jatin Arora, 2Gagandeep , 3Sarvesh S S Rawat4Karthik Srinivasan,5Vikram Puri1-2Department of Electronics & Communication Engineering.3School of Electronics and Electrical Engineering.1CTIEMT, Jalandhar, Punjab, India 2RIET, Phagwara, Punjab, India 3VIT University, Vellore, India 1jatinaroraece 2bbbjollyAbstract- Electrical measurement of quantities plays a crucial role in the real world. Measuring voltage is one of the main tasks for developing large number of applications. This paper is focused on design and development of digital voltmeter using different techniques. It has been shown how to develop a Digital Voltmeter (DVM) from simplest type to professional digital voltmeter. Different types of techniques are adopted for making a voltmeter and the result is compared for testing the accuracy. The simulation of all techniques is done on Proteus ISIS 7.10 and implemented on the hardware. The techniques used for developing the digital voltmeter is comparator based DVM, 8051 based DVM and PIC based DVM. The accuracy of DVMs is4-5Department of Electronics & Communication Engineering4Sri Sai Ram Institute of Technology, Chennai, India 5SBBSIET, Jalandhar, India 3SSS.Sarvesh8884karthik.srinivasan2011 5vikram0317implementation. Block diagram of different techniques used for developing DVM is shown in fig.1.shown by simulation in Proteus ISIS and implementation.through hardwareKeywords- Operational amplifier, Microcontroller, Analog to digital converter, accuracy, simulation.I. INTRODUCTIONMeasuring the voltage is an essential part of any measuringFig. 1 Block Diagram of Various Techniques used for DVMcircuit, thats why DVM is used for themeasurement ofIn PIC based DVM, PIC16F877A microcontroller is usedvoltage 1, 2. In this paper we have used differentwhich has a 10 bit internal ADC with 8 analog channels sotechniques for measuring the voltage classified into two categories that iswhich is mainly analog IC basedthere is no need of an external ADC. This DVM can measurevoltages from multiple sources simultaneously that can betechniques and Microcontroller based Techniques. Analog IC based technique involves comparator based DVM which makes use of operational amplifiers that does not require any kind of programming for its operation. In the comparator based DVM, number of operational amplifiers are used as comparator and output of the comparator becomes high when input becomes more than its reference voltage. Voltage is measured by checking the status of LEDs connected at its output. In the microcontroller based technique we have madevery useful in some applications. In terms of accuracy, thisDVM is much better than other techniques. It can also give the output in millivolts but more accurately.II. COMPARATOR BASED DVMIn comparator based DVM, operational amplifier is used as a comparator for developing the DVM. Comparator mainly compares the input signal with the reference voltage (Vref) and generates the output accordingly. A number of comparators8051 based DVM and PIC basedDVM. AT89S52are connected together andVref of each comparator ismicrocontroller of 8051 family is implemented in conjunction with ADC0804. Voltage which is to be measured is given to ADC and it converts the input voltage to corresponding digital output which is measured by 8051 microcontroller and is displayed on LCD. It is more accurate than comparator based DVM and it is capable of giving the output in millivolts. We have prepared its simulative analysis as well as hardwaredifferent. By doing this when input voltage is zero then theoutput of every comparator will remain low and LEDs remain OFF but when input signal is in between the range of DVM then corresponding LEDs will glow to indicate the value of voltage. When input signal is above the range of DVM then all LEDs will glow. The simulation of comparator based DVM is done on Proteus ISIS 7.10 and is shown in fig. 2 and fig. 3.Fig. 2 Proteus Simulation of comparator DVM at 2 to 3V inputThe range of comparator based DVM is 0-7V but it can be increased by increasing number of comparators. In this DVM the reference voltage (Vref) of each comparator is different i.e. 1V, 2V, 3V, 4V, 5V, 6V and 7V so that it can indicate the range of magnitude of input voltage. As shown in fig. 2 when magnitude of input signal is between 2 to 3V then only first two LEDs will glow to indicate that the signal is more than 2V but third LED and rest of LEDs remains OFF which indicates that input signal is less 3V.Fig. 3 Proteus Simulation of comparator DVM at 5 to 6V inputAs shown in fig. 3 when input signal is between 5V to 6V then first five LEDs will glow to indicate that the signal is more than 5V but the other LEDs remains OFF which indicates that input signal is less 6V. So by this way we can measure input voltage in this method. This technique is not efficient because the accuracy is very poor. For example, when input voltage is more than 2V and less than 3V as shown in fig.2 then we dont know the exact value of voltage whether it is 2.5V or 2.8V but we only get to know about its range that is between 2 to 3V. In case of hardware implementation, operational amplifier like LM358 and LM324 can be used. To improve the accuracy we need to use more and more comparators which make the system more complex and expensive so this method is basic method and it is not used at professional level where accurate reading are required.III. 8051 BASED DVMAfter observing the poor accuracy of comparator based DVM, we use microcontrollers to develop DVM in which we can add further features as required. To meet the aim 8051 based MCU is used. It does not have any internal ADC so external ADC is required to be connected with 8051 for developing DVM. ADC0804 is used for converting the signals. To meet the necessary requirement an attenuator circuit is designed using operational amplifier. The basic configurations of operational amplifier are Inverting amplifier and non-inverting amplifier. The gain of non-inverting amplifier is given as:Af = 1+ Rf/Rin (1) Where, Af is gain, Rf is feedback resistor and Rin is input resistor.If the ratio of Rf/Rin is kept very low so that it can be neglected even then the magnitude of output signal will be equal to input signal and thus attenuator cannot be made using non-inverting amplifier. The other configuration is inverting amplifier whose gain is given as:Af = -Rf/Rin- (2)By keeping the value of Rin more than Rf we can design an attenuator but the output will be of reverse magnitude so we need to connect two inverting amplifiers in series so the o/p will not be of reverse magnitude. For example if we keep the values of Rf and Rin are equal to 1k and 10K respectively in the first stage then the feedback gain Af1 will be equal to -0.1. The second stage which is connected in series has equalvalues for Rf and Rin so its feedback gain Af2 will be -1. The total gain of this configuration will be equal to:Af = Af 1 * Af 2- (3)Af = -0.1 * -1- (4)Af = 0.1- (5)The attenuator is designed by using the inverting amplifier. After observing the mathematical results we simulated it on Proteus ISIS. The simulation of inverting amplifiers as attenuator is shown in fig. 4.Fig. 4 Simulation of inverting amplifier as attenuatorThis final output of inverting amplifiers can be connected at input of ADC so as to limit the magnitude of voltage reaching at ADC input. Voltage divider circuit is best suited for our attenuator because it can operate at higher voltage by selecting the proper value and wattage of resistors. It is also preferable because of its simplicity, less complexity and less cost. We use the voltage divider circuit which divides input voltage by 10 so by doing this 050V DVM can be successfully implemented by using voltage divider circuit with ADC0804 and 8051 microcontroller. The simulation of 8051 based DVM is done on Proteus and it is shown in fig. 5 and fig. 6.Fig.5 Simulation of 8051 based DVM measuring low voltageThe accuracy of the system can be checked by comparing the reading of the LCD with inbuilt voltmeter of Proteus ISIS as shown in fig. 5 and fig. 6. Both low and high voltage is given to ADC0804 in Proteus simulation. 8051 based DVM seems very accurate in simulations as shown in fig.5 and fig. 6Fig.6 Simulation of 8051 based DVM measuring high voltageThe hardware implementation of 8051 based DVM is shown in fig. 7 and fig. 8. The hardware is implemented on generalpurpose PCB and it is remained spare on the left side so as to make improvements or changes to it. The accuracy of this DVM is being checked by comparing the reading on LCD with the multimeter in fig. 7 and fig. 8.Fig.7 Hardware implementation of 8051 based DVM showing accuracy at low voltageFig.8 Hardware implementation of 8051 based DVM showing accuracy at higher voltageThe accuracy on the hardware implementation is not that much which is observed in simulations. Accuracy is one of the most important aspects when designing any measuring circuit so high accuracy is needed 3, 4.IV. PIC BASED DVMThe accuracy was very poor in case of comparator based DVM which was improved in 8051 based DVM. It is further tested using PIC16F877. It has internal ADC of 10 bit with 8 analog channels which directly increases the accuracy and resolution. There is flexibility to set the reference voltage (Vref) externally or internally equals to Vdd. In our design we have used internal reference voltage for internal ADC and two channels of ADC has been used for measuring the voltages from two different sources simultaneously. The range of this DVM is 0 100V so voltages having high magnitude can also be measured by this technique. The voltage at any analog channel should not exceed 5V so voltage divider circuit made of two resistors 2.2k and 100 is implemented which divides input voltage by 20 so as to limit the voltage at analog input. The Proteus simulation of PIC based DVM is shown in fig. 9 and fig. 10. In the simulation the reading accuracy of the system is shown by comparing the reading with internal dc voltmeter of proteus connected at both sources.The system becomes much compact and less complex byFig.9 Proteus ISIS simulation of PIC based DVM measuring low and high voltage from two sourcesFig.10 Proteus ISIS simulation of PIC based DVM measuring average and high voltage from two sourcesAlthough the simulation results of PIC based DVM is very much accurate but it is necessary to implement it in the real world to check the performance and accuracy 7. For developing the hardware in better way, the PCB layout of this technique is being developed in Proteus Ares 7.10. The PCB layout of this DVM is shown in fig. 11.designing the PCB 6. Proteus ARES 7.10 has the availability of 3D visualization of the design which is very important from the designer perspective. 3D visualization of complete design is shown in fig. 12.Fig.12 3D view of PIC based DVM in Proteus ARES 7.10After designing the PCB layout of the system, the PCB is implemented on hardware. We developed the PCB by using screen printing technique. Screen printing technique is used for professionally developing the PCBs and it is adopted by the most of the PCB manufacturers of India. Hardware implementation of PIC based DVM is shown in fig. 13.Fig.13 Hardware implementation of PIC based DVMThe accuracy of this technique needs to be observed on the hardware which is done by comparing the reading of bothsources with the reading of multimeter. In the hardwareimplementation, we dont have the regulated power supply up to 100V but we observed the hardware results by using theregulated power supply up to 30V. Fig. 14 shows theFig.11 PCB layout of PIC based DVM in Proteus ARES 7.10accuracy of the system when comparing the voltage of source 1 with the reading of multimeter. The accuracy of source 2 is also observed in same manner as for source 1 as shown in fig. 15.Fig.14 Accuracy of source 1 being observed by comparing with reading of multimeterFig.15 Accuracy of source 2 being observed by comparing with reading of multimeterPIC based DVM is preferable in all aspects whether it is accuracy, compactness or reliability as compare to other techniques. The fig. 14 and fig. 15 shows that this DVM is very much accurate because the difference between the reading of DVM and professional multimeter is negligible. This technique has the advantage of measuring two voltages simultaneously which is not available in normal multimeter. It can also measure ac voltages by adding precision rectifiers in the system. PIC16F877A is used in this system but other microcontrollers like Atmega 32, MSP430 can also be used depending upon the requirement of the application 5.V. CONCLUSIONDVM is a one of the most important equipment for engineers so this paper describes how we can develop a beginner level DVM to professional level DVM. We showed simulations of every technique and hardware implementation of main techniques. We have used Proteus ISIS 7.10 software for simulation purpose and Proteus ARES 7.10 for PCB designing because Proteus is one of the most popular software used inembedded systems and in other electronic systems. This paper will be very useful for those researchers and engineers who like to experiment more and more to achieve best results.VI. FUTURE RESEARCHAdvancements are always necessary in this technical world. This system can also become digital wattmeter by measuring the voltage from one source and current from other source by using current to voltage converter for it. Then the power consumption can be known by taking the product of both the electrical quantities. Beside this it can also become ac voltmeter by adding precision rectifier made of operational amplifier in it. For making it more attractive, reading of DVM can be transmitted to any distant wirelessly using RF module, Xbee m