Design And Construction Of A Digital Voltmeter Using AVR ATmega8 Microcontroller

ABSTRACT

This work is on a digital using ATMEGA8 microcontroller which is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Digital voltmeter gives a numerical display of voltage, current or resistance by use of an analog to digital converter.

Digital voltmeters can measure a range of alternating current (AC) voltages, direct current (DC) voltages, or both AC and DC voltages. Devices typically display between three and seven digits.

CHAPTER ONE

• INTRODUCTION

1.2                                           BACKGROUND OF THE STUDY

Digital voltmeter is an instrument that measure voltage or voltage drop in a circuit. Digital voltmeter uses solid-state components and display values digitally. Typically, Digital voltmeters (digital volt meters) can be used to locate excessive resistance that may indicate an open circuit or ground. They are also used to identify low voltage or voltage drops that may indicate a poor connection. The positive lead is connected to the circuits positive side and the negative lead is connected to the circuits ground. The digital voltmeters internal resistance is the impedance, which is usually expressed in ohms per volt. This amount is relatively high in order to prevent the device from drawing significant current and disturbing the operation of the circuit being tested. The sensitivity of the Volt meter determines the range of voltages that digital voltmeters can measure.

Digital voltmeters can measure a range of alternating current (AC) voltages, direct current (DC) voltages, or both AC and DC voltages. Devices typically display between three and seven digits. Some digital voltmeters can capture minimum and maximum voltages called spike readings. Others measure the root mean square (RMS), a range of frequencies, or the signal power in decibels. Digital voltmeters are also used to monitor resistance temperature detectors (RTDs), thermocouples, transistors, and diodes. Benchtop, rack mounted, and handheld devices are commonly available. Battery powered units do not require plug-in power. Digital voltmeters with audibility continuity beep when the probes touch. Devices with analog bar graph capabilities display status readings such as battery power, signal level, and continuity.

Some digital voltmeters interface to computers and include integral monitoring software for applications such as data acquisition. Programmable devices allow users to set values that trigger monitoring routines. Data storage, logging, and removable data storage devices are often available. Some digital voltmeters allow users to adjust the sampling rate or provide internal memory. Others include an auto-ranging feature that automatically adjusts the measurement range. Output options include general-purpose interface bus (GPIB), binary coded decimal (BCD), and digital-to-analog (DA). RS232 is a standard communication protocol for serial ports. IEEE 488 is a standard communication protocol for parallel ports.

1.2                                             OBJECTIVE OF THE PROJECT

The main objective of this work is to design a device that will  numerically display of voltage, current or resistance between two points in an electric circuit using a ATMEGA8 microprocessor.

1.3                                         SIGNIFICANCE OF THE PROJECT

The advantages of using Atmega8 microcontroller in this work are as follows:

• It has Low power consumption
• It has a better Amperes display resolution while using low value drop resistor.
• It is much smaller PCB size, only 5cm x 5cm. Still no SMD components.
• It has easy calibration, only one voltage adjust and one ampere adjust preset, no voltage out detection.

1.4                                          ADVANTAGES OF THE PROJECT

• They are more accurate than analog multimeters.
• They reduce reading and interpolation errors.
• The ‘auto-polarity’ function can prevent problems from connecting the meter to a test circuit with the wrong polarity.
• Parallax errors are eliminated. If the pointer of an analog multimeter is viewed from a different angle, you will see a different value. This is parallax error. A digital multimeter’s numerical display solves this problem
• Digital multimeter displays have no moving parts. This makes them free from wear and shock failures.
• The reading speed is increased as it is easier to read.
• Unlike analog multimeters, zero adjustment is not required.
• Digital output is suitable for further processing or recording and can be useful in a rapidly increasing range of computer controlled applications.
• With the advent of Integrated circuits, the size, cost and power requirements of digital multimeters has been drastically reduced.
• Accuracy is increased due to digital readout. You can make mistake in reading the scale in analog multimeter, but digital multimeters have a LCD display to show accurate reading.
• DMMs can be used in testing continuity, capacitors, diodes and transistors. More advanced digital multimeters can also measure frequency.
• The ‘auto-ranging’ feature of a digital multimeter helps in selecting different measurement ranges, which can prevent damage to the meter if the wrong range is selected.
• Portable size makes it easy to carry anywhere.
• They cause less meter loading effects on the circuits being tested.
• Some advanced digital multimeters have microprocessors and can store the readings for further processing.They have very high input impedance.

1.5                                           LIMITATION OF THE PROJECT

1. The LCD display depends on a battery or external power source. When the battery is low, the display will be dim, making it difficult to read.
2. In case of fluctuations or transients, it can record an error.
3. Warming of the ATMEGA8 during its use can change its properties leading to errors in measured value.
4. There is a voltage limitation. If it is increased beyond the limit, the meter will be damaged.
5. The digital nature makes it unsuitable for adjusting tuning circuits or peaking tunable responses.
6. They are expensive due to high manufacturing cost.

1.6                          PROJECT WORK ORGANIZATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to a digital voltmeter. In this chapter, the background, significance, objective limitation and problem of a digital voltmeter were discussed.

Chapter two is on literature review of a digital voltmeter. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.