Design And Construction Of A Digital Multimeter

This work is on the design and construction of digital multi-meter using PIC microcontroller. A multimeter is a tool basically used to measure current, voltage and resistance.. In this system, a typical multi-meter may include features such as the ability to measure AC/DC voltage, DC current, resistance, temperature, diodes, frequency and connectivity. This design uses of the PIC microcontroller, voltage rectifiers, voltage divide, potentiometer, LCD and other instruments to complete the measure. When we used what we have learned of microprocessors and adjust the program to calculate and show the measures in the LCD, keypad selected the modes. The software programming has been incorporated using MPLAB and PROTEUS. In this system, the analogue input is taken directly to the analogue input pin of the microcontroller without any other processing. So the input range is from 0V to 5V the maximum source impedance is 2k5 (for testing use a 1k pot). To improve the circuit adds an op-amp in front to present greater impedance to the circuit under test. The output impedance of the op-amp will be low which a requirement of the PIC analogue input is.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.0     INTRODUCTION

1.1     BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM AND OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• APPLICATION OF THE PROJECT
• SCOPE OF THE PROJECT
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF DIGITAL MULTIMETERS
• HISTORICAL BACKGROUND OF THE STUDY
• GENERAL PROPERTIES OF MULTIMETERS
• OPERATIONAL REVIEW OF A MULTIMETER

CHAPTER THREE

3.0     CONSTRUCTION METHODOLOGY

3.1     BLOCK DIAGRAM OF THE SYSTEM

3.2      CIRCUIT DIAGRAM

3.3      CIRCUIT OPERATION AND DESCRIPTION

CHAPTER FOUR

4.0     TESTING AND RESULTS

• CONSTRUCTION PROCEDURE AND TESTING
• CASING
• PACKAGING
• MOUNTING PROCEDURE
• TESTING
• RESULT ANALYSIS
• MEASUREMENT SAFETY

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

• INTRODUCTION

Multimeters as the name suggest the meters that we use to measure multiple quantities with the same instrument. The most basic multimeter measures voltage, current, and resistance. Since we use it for measuring current (A), voltage (V) and resistance (Ohm), we call it as AVO meter. We can categorise the multimeters into two groups, namely analog multimeter and digital multimeter. This work discusses about digital multimeter [3].

1.1                                           BACKGROUND OF THE STUDY

A multi-meter or a multi-tester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multi-meter may include features such as the ability to measure voltage, current and resistance. Modern multi- meters are often digital due to their accuracy, durability and extra features. In a Digital Multi-meter the signal under test is converted to a voltage and an amplifier with an electronically controlled gain preconditions the signal. A Digital Multi-meter displays the quantity measured as a number, which prevents parallax errors. The inclusion of solid state electronics, from a control circuit to small embedded computers, has provided a wealth of convenience features in modern digital meters.

1.2                                                  PROBLEM STATEMENT

Nowadays many measurement instruments have been used in all laboratories throughout the world. Unfortunately, their accuracies are mostly proportional to the time period. As time passes, they may function incorrectly and generate some errors. The mistaken results from such instruments can cause serious problems in economic system and life safety since they will be used for validating product standards in the importing and exporting industries. In order to ensure that they work perfectly, the calibration process is required. In the past, the calibration has to be performed manually and this process usually takes long time. Presently, fully automatic calibration systems have been used worldwide and they play an important role in the calibration of measurement instruments. They can improve measurement accuracy, repeatability and minimize routine jobs.

1.3                                                   AIM OF THE PROJECT

The main aim of the project is to build a hand-held device that uses LCD to display readings useful for basic fault finding and field service work, or a bench instrument which can measure to a very high degree of accuracy.

1.4                                            OBJECTIVES OF THE PROJECT

At the end of this work, the student involves shall be able to build a simple digital multimeter that is capable of measuring current, voltages, temperature and resistance.

1.5                                          ADVANTAGES OF THE PROJECT

1. They are more accurate than analog multimeters.
2. They reduce reading and interpolation errors.
3. The ‘auto-polarity’ function can prevent problems from connecting the meter to a test circuit with the wrong polarity.
4. 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
5. Digital multimeter displays have no moving parts. This makes them free from wear and shock failures.
6. The reading speed is increased as it is easier to read.
7. Unlike analog multimeters, zero adjustment is not required.
8. Digital output is suitable for further processing or recording and can be useful in a rapidly increasing range of computer controlled applications.
9. With the advent of Integrated circuits, the size, cost and power requirements of digital multimeters has been drastically reduced.
10. 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.
11. DMMs can be used in testing continuity, capacitors, diodes and transistors. More advanced digital multimeters can also measure frequency.
12. 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.
13. Portable size makes it easy to carry anywhere.
14. They cause less meter loading effects on the circuits being tested.
15. Some advanced digital multimeters have microprocessors and can store the readings for further processing.
16. They have very high input impedance.

1.6                                           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 meter during its use can change its properties leading to errors in measured value.
4. The A/D converter has a limitation on word length which can cause quantization noise giving rise to error in measured value.
5. There is a voltage limitation. If it is increased beyond the limit, the meter will be damaged.
6. The digital nature makes it unsuitable for adjusting tuning circuits or peaking tunable responses.
7. They are expensive due to high manufacturing cost.

1.7                                          APPLICATION OF THE PROJECT

Digital multimeter is one of the trusty workhorses of the electronics test industry for basic fault finding and field service work which is also used by:

1. Electronics hobbyist
2. Electronics technicians

• Electronics repairers

1. Electronics labs
2. Electricians, etc.

1.7                                                         SCOPE OF THE PROJECT

A digital multimeter is a device which provides combined functionality of ammeter, voltmeter and ohmmeter. It is commonly known as DMM. It is most widely used due to its small size, price and ease in operation. A digital multimeter has an analog/digital converter that provides a digital readout.

This system is to measure AC/DC voltage, current, diodes, temperature, connectivity, frequency and resistance using PIC microcontroller. To carry out the design consideration and production of a useful consumer product of PIC microcontroller. The whole process of the digital multi-meter is controlled by PIC 16F887 microcontroller.

1.8                                                         PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.