This project is a digital voltmeter
that uses the Integrating converter (ICL71O7) from INTERSIL. The lCL71O7 is a
high performance, low power, 35 digit analog to digital converter The IC
includes internal circuitry for seven segment decoders, display drivers,
reference voltage source and a dock. The power dissipation is less than 10mW
and the display stability is very high. The working of this electronic circuit
is very simple. The voltage to be measured is converted into a dig equivalent
by the analog to digital converter (A inside the IC and then this digital
equivalent is decoded to the seven segment format and then displayed. The ADC
used in 1CL7107 is a dual slope type ADC. The process taking place inside our
ADC can be stated as follows. For a fixed period of time the voltage to be
measured is integrated to obtain a ramp at the output of the integrator. Then a
known reference voltage of opposite polarity is applied to the input of the
integrator and allowed to ramp until the output of integrator becomes zero.
The problem that is usually
encountered in using the analog display of voltmeter is that there is not much
accuracy in the readings and the person using it has to calculate and interpret
in hundred, kilo or mega volts. The analog voltmeter is displayed using a scale
and a pointer, due to this, there is much parallax and human error in the
readings which makes it less accurate.
The solution to the problem outlined above
is to design a digital voltmeter which will eliminate parallax error and reduce
human error and thereby giving high level of accuracy in the readings.
Another interesting thing about this digital
voltmeter is that it uses LED (Light Emitting Diode) type, seven segment
display and therefore can be seen clearly in darkness which most of analog
voltmeter do not have.
Though the cost of producing a digital
voltmeter is more than that of an analog type, but the advantage of a digital
voltmeter is much more than of an analog type.
In consideration of the problems and
solution suggested, it is concluded that a digital voltmeter is very useful and
it will make life easier.
TABLE OF CONTENTS
1.1 Aims and objectives
1.2 Analog voltmeter
1.3 Digital voltmeter
1.4 Differences between analog and digital
1.5 working operation of this project
2.0 Literature review
2.1 Theory and operational principles of
2.4 Analog to digital converter
2.5 Seven segment display
2.7 differences between multi-meter and
3.0 Design, Methodology and Operation
3.1 General description 25
3.2 Circuit diagram of a digital
3.3 Analog to digital converter ICL 7107
3.4 How the project works
3.5 Procedure for construction (design)
3.6 parts listed of components used
3.7 Challenges encountered and solution
3.8 Power supply
4.0 Testing and conclusion
4.1 Measuring voltage
5.0 Recommendation and observation
Electronic s system is a system that
deals with the flow of electrons. Resistance, voltage and current are the
basics of electronics. Electronics system refines, extends, supplements human
facilities and gives us the ability to perceive, communicate, calculate,
remember, reason and so on. General It makes life easier. Electronics device in
modern days are now replacing electromechanical device. For example, an
automated electronic switch that is programmed to operate at a specific time
under a S condition makes a mechanical (manual) switch useless. Electronics
system is preferable to mechanical system because it has a high degree of
accuracy and efficiency.
Most electrical quantities are
measured with a device called a meter. Voltage is measured with a voltmeter,
current with an ammeter, resistance with an ohmmeter and power with a
wattmeter. A meter that measures only one of the above quantities is cared a
voltmeter. Voltmeters are often permanently connected (wired) into a circuit to
provide continuous monitoring of an electrical quantity.
Electronics system is classified into
two pan that is Analog and Digital electronics system. Analog system is a
system that deals with discrete values of quantify and changes its output value
linearly with the change in input value. Example is scale and a pointer device
such as an analog multi-meter, a weight scale, analog voltmeter, analog clocks
etc. A digital system is the one that produces only two output levels based on
the range of values of the input that is its output is represented by two
discrete levels only which is ‘1’ and ‘0’. This land values are called Sits
taken from the word “Binary Digit”. The bits are used to perform many
arithmetic and logical operations. The land 0 values are otherwise known as
logic levels or logic states. The 0 level is called the LOW level while the 1
level is called the HIGH level. With this bit, it is easier for computer to
process data and gives out the required output because it is only dealing with
land 0 values. This makes it possible for me to design a digital voltmeter that
will display values in form of figures instead of scale and pointer as to the
case of an analog voltmeter.
The digital voltmeters are instruments
that measure voltage or voltage drop in a circuit, they use solid-state
components and display values digitally. Typically, d voltmeters are 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
Digital voltmeters are connected in
parallel with the circuit being tested so that the meter can tap a small amount
of current. 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 input 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 current meter and the value of the series
resistance determine the range of voltages that dig voltmeters can measure.
Digital voltmeters are usually
designed around a special type of analog-to-digital converter called an
integrating converter. Voltmeter accuracy is affected by many factors,
including temperature and supply voltage variations. They 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 also capture minimum and maximum voltages called spike
1.1 AIMS AND OBJECTIVE OF THIS PROJECT
aim of this project is to design and construct a digital voltmeter using I
objectives are as follows:
- A digital voltmeter or DVM is
used to take highly accurate voltage measurement and easy to read from
- Digital voltmeter output is in numerical
form displayed on an LED (light emitting diode).A digital voltmeter
typically consists of an analog to digital converter (A/D) with a digital
display, The analog signal is converted into a digital code proportionate
to the magnitude of the signal.
- Digital voltmeter measurements
have a far less uncertainty (about 0 or less). The cost of constructing a digital
voltmeter is low and few external components are used.
- Digital voltmeter possesses some
few components, small in size and easy to construct with simple
- A digital voltmeter mo has
superior resolution and a higher order of accuracy with plus or minus 0.5%.it
also indicates a negative quantity when polarity is reversed.
1.2 ANALOG VOLTMETER
An analog voltmeter uses the needle
pointer to read out values. With this meter, the needle can point anywhere on
the scale. When an analog meter is read, the reacting is generally taken to the
nearest minor division mark. If the pointer is half way between marks, it is
read as a half-division. Before reading a meter scale, you must figure out the
value of each division of the scale. Look at the scale on the meter in figure
1.1; notice that there is a heavy line represents five units. Now count the
numbers of divisions (called minor divisions) between 4 and 5 since there are
five minor divisions between 4 and 5, each minor division has a value of 0.2
units. Therefore, each minor division on the scale represents 0 ampere, suppose
the needle (pointer) on the meter in figure 1.1 is pointing to the second mark
to the right of the 7 mark. The meter would be indicating 7.6 amperes.
1.1: DIAGRAM OF AN ANALOG READOUT.
1.3 DIGITAL VOLTMETER
The voltmeter shown in
figure 1.2 eliminates the need to decide which mark is closest to the pointer.
There is no guesswork in trying to decide whether the meter reading is 184.9 or
184.8.Digital voltmeters are usually specified by the number of digits in their
readout When the most significant (left-most) digit can be only a 0 or a 1, it
is counted as a ha 200-volt digital voltmeter in figure 1.2 is a three and half
digit meter. Even though it is called a 200-volt meter it can measure a maximum
of 199.9 volts.
1.5 WORKING OPERATION OF THIS PROJECT
This digital voltmeter project is
ideal to use for measuring the output voltage of a DC (Direct Current) power
supply. It includes a 3.5-digit LED display with a negative voltage Indicator.
The 1CL7107 is a high performance, low power, 3.5 digit analog to digital converter.
The IC Includes internal circuitry for seven segment decoders, display drivers,
reference voltage source and a clock. The power dissipation is less than 10mW
and the display stability is very high.
It measures DC voltages from 0 to
199SV with a resolution of 0.IV. The voltmeter is based on single ICL71O7 chip
and may be fitted on a small 3cm x 7cm printed circuit board. The circuit
should be supplied with a by voltage supply and consumes only around 2SmA. 220
Ohm resistor should be connected to the PIN4 on the first LED (LIGHT EMITTING
DIODE) display. The voltmeter can also be configured to measure different
voltage ranges and Use 10K potentiometer to set the reference voltage between
PIN 35 and PIN 36 of the ICL7Wq IC to display higher voltage resolution. P IM
with 100K resistor will allow to measure 0- 19.9W voltages with 0.0W (l0mV)
The working of this electronic circuit
is very simple. The voltage to be measured is converted into a digital
equivalent by the ADC inside the IC and then this digital equivalent is decoded
to the seven segment format and then displayed. The ADC used in 1CL7107 is dual
slope type ADC. The process taking place inside our AIX can be stated as
1. For a fixed period of time the voltage
to be measured is integrated to obtain a ramp at the output of the integrator.
2. Then a known reference voltage of
opposite polarity is applied to the input of the integrator and allowed to ramp
until the output of integrator becomes zero.
3. The time taken for the negative slope
to reach zero is measured in terms of the IC clock cycle and it will be
proportional to the voltage under measurement.
4. In simple words, the input voltage is
compared to an internal reference voltage and the result is converted in a digital
The resistor R2 and C are used to set
the frequency of IC Internal clock Capacitor C2 neutralizes the fluctuations in
the internal reference voltage and increases the stability of the display.R4
controls the range of the voltmeter. Right most three displays are connected so
that they can display all digits. The left most display is so connected that it
can display only “1” and “-“. The pin 5 (representing the dot) is connected to
ground only for the third display and its position needs to be changed when you
change the range of the volt meter by altering R4. (R4=1.2K gives O-20V range,
R4=IZK gives O-200V range).
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