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Voltage is a fundamental quantity that is important in every phase of electrical engineering from power system to voltage inside VLSI chips. Of The need to measure the output voltage of a supply is very important meanwhile, The voltmeter is an instrument for measuring voltage, it could be digital or Direct voltage, meanwhile, the rectification process of the alternating voltage using diode, make, it more possible for ac voltages to be measured.

However, the need for modernization makes it necessary to use computer to view the output of the voltage in either graphical or numerical form. Chapter one introduces the topic captioned “Ac voltmeter design and construction. Using computer interface” Chapter two is on the literature review of the work, whereby all the works of inventors who in one way or the other contributed to the improving of the voltmeter were reviewed. Chapter three is on the components used to make the project workable. Chapter four speaks on the design of project, the mode of operation, while chapter five which is the last chapter, is on the conclusion and the recommendation on the project as well as the books and other sources of the information.


Title Page - - - - - - - - - i

Certification - - - - - - - - ii

Dedication - - - - - - -- - iii

Acknowledgement - - - - - - - iv

Abstract - - - - - - - - - v

Table of contents - - - - - - - vi-vii


Introduction - - - - - - - - 1-7


Literature Review - - - - - - - 8-12


Components used and Functions - - - - 13

Integrated circuit (Adc 0804) - - - - - 13-14

Diode - - - - - - - - - 14-15

Switches - - - - - - - - - 16

Transistors - - - - - - - - 17-18

Resistors - - - - - - - - - 18-19

Capacitors - - - - - - - - 19-20

Transformers - - - - - - - - 21-22


Working principle - - - - - - - 23

Procedure for building the circuit - - - - 24-25

Likely faults - - - - - - - - 25-26

Circuit diagram - - - - - - - - 27

Precautions when installing the component - - 28


Conclusion - - - - - - - -29-30

Recommendation - - - - - - -30-31

Reference - - - - - - - - 32



A voltmeter is an instrument that measures voltages of either direct or alternating electric current on a scale usually graduated in volts millivolts (0.00V) or kilovolts (1000 volts) the typing commercial or laboratory standard voltmeter in use is likely to employ an electromechanically mechanism in which current flows. Through turns of wire is translated into a reading of voltage. Other types of voltmeter which use electrostatic forces and these are only voltmeters to measure voltage direct rather than by the effect of current. The potentiometer operates by comparing the voltage to be measured with known voltage. It is used to measure very low voltages the electronic voltmeter which has largely replaced the vacuum – tube voltmeter, uses amplification or reification (or both) to measure either alternating or direct – current voltages the current needed to activate the meter movement is not taken from the circuit being measured, hence this type of instrument does not introduce errors of circuit leading.

However, the growth in technology, it has necessitated the use of computer for controlling the output of the voltmeter. Whereby, the display of the voltage being read is being viewed from the monitor. His kind of display could be either graphical or numerical, but the most popular type is that of numerical display, this is achieved by a series of switching actions of a micro controller, whereby the internal flow at the analog inputs.

Meanwhile, one cannot freely talk about the computer controlled ac voltmeter, without first discussing the Analog is digital (AD) converter which has many degrees of complexity associated with testing an (A/D) converter, one of the simplest tests is to apply a known analog input voltage to the converter and use LEDS to display the resulting digital output code.


Ac electromechanical meter movement comes in two basic arrangements. Those based on Dc movement designed and those engineered for ac use. Permanent – magnet moving coil (pmmc) meter movement will not work correctly if directly connected to alternating current, because the direction ofneele movement will change with each half cycle of the AC.

i. Passing Ac through D’ Arsonval Meter

This causes useless flutter of the needle. In order to use a Dc style, meter such as C’ arsenal design the alternating current must be rectified into Dc. This is most easily accomplished through the use of devices called Diodes we will see diodes used in a circuit that demonstrates, the creation of harmonic frequencies from a distorted (or rectified) sine wave. Another strategy for a practical ac meter movement is to redesign the movement without the inherent polarity sensitivity of the Dc types. This means that the use of permanent magnet should be avoided.

ii. Iron Vane Electromechanically Meter Movement

Electrostatic attraction between two metals plates separated by air gap is alternative mechanism for generating a needle –movement force proportional to applied voltage. This works just as well for Ac as it does in dc or probably poorly. The force involved is small much smaller than the magnetic attraction is small much smaller than the magnetic attraction between an energized coil and iron vane and as such these “electrostatics meter movement tends to be fragile and easily disturbed by physical movement.

With some the advantages and disadvantages of these meters movement technologies having been discussed already, there is nether factor crucially important to be designer and user of ac metering instrument to be aware of. This is the issues of Rms measurement. As we already know, Ac measurements are often cast in a scale of Dc power equivalent called RMSCRoot- Mean –Squired for the sake of meaningful comparism with Dc and with other Ac waveforms of varying shape. None of the meter movement technologies boyar discussed in gently measures RMS value of an Ac quantity. Meter movement relying on the motion of mechanical needle (“rectified D’ Arson Val, Iron-vane and Electrostatic) all tend to mechanically average the instantaneous values into an overall average value for the waveform. This average value is not necessarily the same as RMS, although many times it is mistaken as such. Average and RMS seems to be the kind of measurement most people are interested in obtaining with an instrument and electromechanical meter movement naturally deliver average measurement rather than RMS, what are Ac meter designers to do? Cheat of course! Typically the assumption is made that the wave form shape to be measured is going to be sine and then the meter movement scale is altered by the appropriate multiplication factor. For sine waves we see that RMS is equal to 0.77 times the peak value while average is 0.637 times the Reek, so we can divide one figure by the other to obtain an average to RMS conversion factor of 1.109.

=> 0.707 =1.1099


With square waves, the RMS and Average value are identical! An Ac meter calibrated to accurately read RMS voltage or current on a pure sine wave will not give the proper the proper value while indicating the magnitude of anything other than a perfect sine wave. This includes triangle waves, square waves, or kind of distorted sine wave. With harmonics becoming an ever- present phenomenon in large Ac power systems,. This matter of accurate RMS measurement is no small matter.

This material content is developed to serve as a GUIDE for students to conduct academic research


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