CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the study
Our World has change a great deal, with the advent of information technology, sudden and
unforeseen dangers have been reduced, a great deal.
The significance of this information technology is that it has penetrated almost every aspect
of science, technology and the society at large, most especially in our electronic equipment,
this information technology has gone as far as making provision for an input signal or
warning system in most of our electrical systems and it has given birth to what we popularly
known as power sensor’’ (Okeke, 2021).
A Sensor also called a detector is a converter that measures a physical quantity and converts
it into signal which can be read by an observer or by an instrument (today mostly electronic)
sensors are used in everyday objects such as touch – sensitive elevator buttons, Lamps which
dim or brighten by touching their base several applications of sensors include cars, machines,
medicine, manufacturing and robotics (Newness, 2020).
The sole aim of this project, is to build up a car battery alarm which has being identified as a
low voltage power sensor and it is used in Detecting cell design faults, circuit interruption
failures, fan or pump failure etc. in a car (Thereja, 2022).
A good sensor is always sensitive to the measured property such as voltage and temperature
etc. it does not influence the measured the property.
The battery level indicator will alleviate the Difficulty we would have face because the
automobile battery will not run down unnoticed but sound an alarm in order to unable the
user initiate a correction measure before the need arises (Mercy 2024).
Simple Battery Level Indicator Circuit designed by using IC LM3914 – dot/bar display driver
from Texas Instruments. This circuit detects battery charging level and indicates the
percentage of charge through 5mm LEDs. First three Red LEDs are indicates 0 to 30
percentage battery, Orange Color LEDs are indicates 40 to 60 percentage battery level and
Green LEDs are indicates 70 to 100 percentage charge level of battery (Okeke, 2023).
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This Battery Level Indicator Circuit designed to be employed in 12V battery environment. IC
LM3914 is a monolithic Integrated circuit that senses Analog Voltage levels and drives 10
LEDs, and also Bar graph LEDs. This IC LM 3914 contains its own adjustable reference and
accurate 10 step voltage divider (Okeke, 2023).
Battery level indicator will let us know the states of battery of a device just by glowing the
number of LED’s. For example four LED’s are glowing means battery capacity is 40%. You
can use this circuit with your inverter or with your car battery; it will give you indication
about your battery status. So before your battery dies you can recharge it. Advantage of this
circuit is it does not require power supply; it will take power supply from the battery of the
device itself. This simple circuit is based on single IC LM3914 with few more discrete
components. LM3914 is a monolithic integrated circuit which senses the analog voltage and
derives 10 LED’s providing a linear analog display.In this paper, we will show how to design
a simple Battery Level Indicator Circuit using easily available components. Battery level
indicator indicates the status of the battery just by glowing LED’s. For example six LED’s
are glowing means battery capacity 60% remains. This article will explain how to design
battery level indicator. We can use this circuit to check car battery or inverter. So by using
this circuit, we can increase the lifetime of battery (Abdelsalam, 2021).
1.2 Aim and objectives of the study
The aim of this is to design and construct battery level indicator circuit
The objective of this study is to:
1. To design a battery level indicator circuit.
2. To construct a battery level indicator circuit
3. To know the importance of battery level indicator circuit
4. To evaluate the essential parameter of the input and output of the circuit
1.3 Significance of the study
The significance of this project goes a long way to reveal the importance of a low voltage
power sensor in a car batter. The purpose of this alarm indicating device gives warning to
automobile users. It will help car users to check their battery system as a part of the normal
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morning start up routine and also helps the user to detect if the battery bought is exactly 12v.
Thus, a power sensor will help to reduce the level of risk and also preserve human life.
1.4 Scope and limitation of the study
The study will be base on the design and construct battery level indicator circuit as a case
study. It is restricted to the use of signals in reducing unforeseen danger. Critical emphasis
will be placed on voltage, Diodes, Capacitors transducer, as examples of component of a
battery level indicator.
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CHAPTER TWO
LITERATURE PREVIEW
2.0 Introduction
The battery level indicator is a constructed device used in monitoring the condition of a
battery in any electrical system that utilizes Battery as a source of electrical energy. It consist
of both passive and active component which are designed in such a way that when the
condition of the battery is low, it will detect and raise an alarm to attract the user’s attention
(Theraja, 2021).
Battery level indicator will let us know the states of battery of a device just by glowing the
number of LED’s. For example four LED’s are glowing means battery capacity is 40%. You
can use this circuit with your inverter or with your car battery; it will give you indication
about your battery status. So before your battery dies you can recharge it. Advantage of this
circuit is it does not require power supply; it will take power supply from the battery of the
device itself. This simple circuit is based on single IC LM3914 with few more discrete
components. LM3914 is a monolithic integrated circuit which senses the analog voltage and
derives 10 LED’s providing a linear analog display (Theraja, 2015).
Battery voltage which is also referred to as nominal voltage is the amount of voltage that a
battery outputs across its terminals when fully charged. Besides the mAh rating, each battery
has a nominal voltage specified in the spec. For instance, a 9-volt battery provides 9 volts
across its terminals when connected in a circuit. The voltage decreases during operation and
usage hence become less and less. The AA batteries usually have a voltage range of 1.2 - 1.5
volts. It is important however to check the specification as some types of batteries have
totally different nominal voltage (Gary and Beukes, 2020).
Capacity of the rechargeable batteries and its variation is the main idea explored in this
project. It is therefore necessary to highlight the meaning of battery capacity without
confusing battery capacity with the percentage of terminal voltage to charge voltage. During
redox reaction of a particular cell, the driving force which can as well be pull of electrons is
called cell potential (e.m.f) and its unit is volt (V). Volt can basically be defined as 1 joule of
work per coulomb of charge transferred. From this definition it is clear how electricity is
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generated from power sources operating under the same principle (Hai-bo and Xin-jian,
2021).
Fig 2.1: Battery Level Indicator: (Theraja, 2015)
In this paper, we will show how to design a simple Battery Level Indicator Circuit using
easily available components. Battery level indicator indicates the status of the battery just by
glowing LED’s. For example six LED’s are glowing means battery capacity 60% remains.
This article will explain how to design battery level indicator. We can use this circuit to
check car battery or inverter. So by using this circuit, we can increase the lifetime of battery
(Herves, 2022).
2.1 Review of Past Projects
Battery level indicator is also incorporated to show when the battery is low and when the
batter is full. In the circuit for battery full and battery low is the comparator. A comparator is
a device that takes two inputs and gives output after comparing the two inputs (Okeke, 2012).
The output is in form of the input of the either the inverting or the non-inverting, depending
on what it is meant for. If the inverting input is higher than the non-inverting input, the output
will be high after comparing the two, but if the inverting is less than the non-inverting, the
output will be the reference value of the non-inverting. In this case, the reference value is the
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voltage supply, when the voltage at the inverting is less than the noninverting, the output will
be the input voltage (Murrain Webster, 2012).
Batteries are not all equal even if they have the same chemical reactions. Battery
development trade-off is between energy and power. A C-rate is the measure at which a
battery is discharged relative to its maximum capacity. An E-rate on the other hand describes
a discharge power. The energy stored in a battery is measured in Watt-hours (Wh) or ampere-
hours (Ah) (Hohm, 2020).
This is used to indicate battery low and battery full with the aid of a voltage fixing diode
(zener diode). The room for future expansion is good for any electrical project. To supply
1kVA, a combination of six MOSFETs in cascade can serve the purpose, but for this project,
there is anallowance in the number of MOSFETs used. Fourteen MOSFETs are incorporated
in the design, these can supply five (5) times of 1 kVA, that is, it can supply up to 5 kVA
with an increase in the number of battery to be used. It can go as far as supplying five (5)
times the power that is used for in this project (Thereja, 2012).
The power source switching has been made automatic by 555 timer IC which controls the
switching from AC main and battery supply. The 555 timer IC is an integrated circuit that can
function in either monostable or astable mode. In the astable mode, the 555 timer can be used
as a timer; it engages and dis-engages at certain time controlled by its clock. This timing is to
delay the supply by some microseconds before the power comes up. The delay is to prevent
transient current from the circuit (Theraja, 2015).
Transient current are the surge current which is higher than the normal current. Surge current
can damage electrical appliances. This surge current is imminent when the power is just
supplied. With the combination of the timer and the capacitor, the surge will not have an
influence on the appliances. The capacitor absorbs the surge and the delay does the function
of delaying the time and allows every surge to be absorbed before the circuit is engaged with
power. This will make the inverter safe to use (Theraja, 2015).
In the inverter is also the charging circuit. When the battery goes down in voltage, the
inverter will definitely go off. Then there will need to charge the battery and this has been
incorporated in the inverter. The inverter battery charging circuit contains basically the step-
down transformer and the rectifier (Jayawardena, 2020).
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The step-down transformer steps down the voltage from the mains to the required voltage
needed to charge the battery. In this case, it will step down from 220V/AC to 15V/AC before
the voltage is rectified. In the charging circuit, the voltage regulator maintains the amount of
voltage coming out of the charging circuit to the required voltage. To show the voltage output
of the inverter, a meter indicator is used, this increases the viability of the inverter as it tells
the user when the battery is going low even before the indicator indicates that the battery is
low (McLamb, 2021).
Fig. 2.2: Battery level (Gary and Beukes, 2020)
Normally, in mobile phones, the battery level is shown in dot or bar form. This lets you easily
recognise the battery level. Here we present a circuit that lets you know the battery level of a
device from the number of LEDs that are glowing. It uses ten LEDs in all. So if three LEDs
glow, it indicates battery capacity of 30 per cent. Unlike in mobile phones where the battery-
level indicator function is integrated with other functions, here only one comparator IC
(LM3914) does it all (Kerekes and Teodorescu, 2021).
The LM3914 uses ten comparators, which are internally assembled in the voltage divider
network based on the current-division rule. So it divides the battery level into ten parts
(Lamba, 2022).
The circuit derives the power supply for its operation from the battery of the device itself. It
uses ten LEDs wired in a 10-dot mode. The use of different coloured LEDs makes it easier to
recognise the voltage level on the basis of the calibration made. Red LEDs (LED1 through
LED3) indicate battery capacity of less than 40 per cent. Orange LEDs (LED4 through
7
LED6) indicate battery capacity of 40 to less than 70 per cent and green LEDs (LED7
through LED10) indicate battery capacity of 70 to under 100 per cent. The brightness of the
LEDs can be adjusted by varying the value of preset VR2 between pins 6 and 7 (McLamb,
2021).
The circuit derives the power supply for its operation from the battery of the device itself. It
uses ten LEDs wired in a 10-dot mode. The use of different coloured LEDs makes it easier to
recognise the voltage level on the basis of the calibration made. Red LEDs (LED1 through
LED3) indicate battery capacity of less than 40 per cent. Orange LEDs (LED4 through
LED6) indicate battery capacity of 40 to less than 70 per cent and green LEDs (LED7
through LED10) indicate battery capacity of 70 to under 100 per cent. The brightness of the
LEDs can be adjusted by varying the value of preset VR2 between pins 6 and 7 (Mohan et
al., 2023).
Diode D1 prevents the circuit from reverse-polarity battery connection. The tenth LED glows
only when the battery capacity is full, i.e., the battery is fully charged. When the battery is
fully charged, relay-driver transistor T1 conducts to energise relay RL1. This stops the
charging through normally-open (N/O) contacts of relay RL1 (Niehage, 2020).
For calibration, connect 15V variable, regulated power supply and initially set it at 3V.
Slowly adjust VR1 until LED1 glows. Now, increase the input voltage to 15V in steps of
1.2V until the corresponding LED (LED2 through LED10) lights up. Now the circuit is ready
to show any voltage value with respect to the maximum voltage. As the number of LEDs is
ten, we can easily consider one LED for 10 per cent of the maximum voltage. Connect the
voltage from any battery to be tested at the input probes of the circuit. By examining the
number of LEDs glowing you can easily know the status of the battery. Suppose five LEDs
are glowing. In this case, the battery capacity is 50 to 59 per cent of its maximum value.
Assemble the circuit on a general-purpose PCB. Calibrate it and then enclose in a box
(Obaidullah, 2022).
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Fig. 2.3: Battery circuit (Obaidullah, 2022).
Batteries come in standard cells which describe the size and shapes. They are denoted by
letters such as AAA, AA, C, or D. AA for instance references a specific shape, size and style
of the cell. The rating on each battery, describes its capability to supply power at the stated
rate (Sooriyaarachchi et al., 2021).
Smart batteries and smart chargers should not be confused as the terms can be used closely. A
smart battery contains a chip which can communicate with a smart charger while being
charged about its charging conditions and behaviour. This therefore means that smart
batteries cannot be charged by simple chargers. Smart chargers however can charge both
smart and any other type of battery as long as power rating conditions are met (Mehreen,
2022).
This form of charging employs single low level current set at fixed rate to the discharged
battery. Chargers used for this form of charging vary the voltage applied to the battery for
constant current maintaining. The common types of batteries that are charged with this
method include NiCad, NiMH and lithium-ion. When the voltage reaches the level of full
charge, the current is switched off. Higher rates of current level would charge the battery in a
short time and in this case, appropriate charge termination method would be applied to avoid
overcharge (Kabeel, 2020).
Batteries like NiMH and Lithium ion can still suffer from overcharge if left to charge for
longer time under this method. Lead acid and NiCad can however tolerate overcharge at low
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charge rate without serious damage. This is so because of their internal chemistry. For
instance while NiCad’s recombination process pertain to keep the voltage down to a safe
level, NiMH’s overcharge produces gases which lead to increased temperature. For this
reason, NiMH cells have a range of between 0.4 C to 0.1 C slow charging rates. This rate of
charging is not only safe for charging certain types of batteries but also less expensive as the
chargers used are simple or dumb. The charging time is however long and batteries like
NiMH are not protected from a possible overcharge (Pratik, 2023).
In respect to rechargeable batteries, discharging a battery is seen as the reverse process of
charging. It can simply be described as the function of removing the current from a battery.
However, for better understanding and demonstration of the weight that this section has in the
project, a need to restate the purpose of a battery cannot be avoided (Alswidi, 2024).
A battery is meant to store energy and release it at an appropriate time and in a controlled
manner to satisfy the power specifications for the portable electronics. The technology that
highlights the process of storing energy, as discussed in chapter 2, and the process of passing
energy into the cell, as described in chapter 4, is one part. The second part is the satisfaction
of the load demands, which is partly demonstrated in chapter 3. The other part that this
chapter addresses is the delivery of the stored energy without over discharging or without
leaving usable energy behind when the process is terminated (Rafd, 2020).
The battery performance increases with temperature. This means that increasing temperature
has a positive effect on the discharge capacity as long as extreme temperature level is not
reached. Just like the effects of temperature during charging, extreme high temperatures will
reduce the battery capacity hence less energy delivery. This factor is true on most types of
batteries except for the case of Li-ion which is not affected much with an extreme high
temperature (Rafd, 2020).
The operation of the circuit can be verified through calculations based on the properties of
each component. An example of calculation based on the components value shown in figure
13 to derive the current through the battery is described in the following statements. First,
BD135 is a NPN transistor with a DC current gain of 40-240 according to datasheet. One can
begin the calculations from various points but if the analysis is from the source voltage, then
a voltage drop of around 0.8v and 1.2v is expected across the diode and the battery under
charge (Branko et al., 2024).
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Batteries with capacity percentages below 60 fall under fair capacity state category but with
a warning stating serious drop in capacity. The user interface in LabVIEW will show a
blinking LED for the percentages below 40% to incur the seriousness of the level of capacity
degradation of the respective batteries (Pratik, 2023).
The rate of charging or discharging has significant effect on the battery capacity irrespective
of type. High rates of charging need to be controlled by the use of smart chargers or close
supervision of the process. Overheating caused by fast chargers tend to affect the
electrochemistry of the battery. This has a negative effect on the battery capacity. Over-
discharge on the other hand leads to battery capacity drop (McLamb, 2021).
The other major maintenance methods are battery type related. NiCad for instance has good
capacity and a reasonable shelf life but suffers from the “memory effect”. This effect can be
reduced by making sure the battery is used until fully drained to minimize crystal build up.
Performing deep discharge is another way to limit the memory effect but it should be done
time after time and not every now and then. Every month is recommended for the batteries
used more often (McLamb, 2021).
NiMH has similar advantages to NiCad besides not suffering the memory effect. However,
they experience high self-discharge rate while not in use or in storage. A recommended way
to maintain the battery capacity is to keep it trickle charging while not in use (Elisa et al.,
2021).
LM3914 IC FEATURES
1) Internal voltage reference from 1.2 to 12v DC.
2) Programmable output current 2mA to 30mA.
3) LED driver outputs are current regulated.
4) No multiplexing interaction between outputs.
5) It supports wide range of temperature from 0 to 70 degree Celsius.
6) For bar graph display – connect 9th pin of IC to the supply
7) For dot display – leave the 9th pin of IC
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We can also connect different colour LED’s to indicate the status. Connect D1 to D3 red
LED’s which indicates shut down stage of your battery and use D8-D10 green colour LED’s
which indicates 80 to 100 percentage of the battery and use yellow colour for remaining
(Pratik, 2023).
Advantages
1) Some cordless tools have a battery-level indicator which lets us know how much battery
power the tool has left. And this feature is like having fuel gauge on a car.
2) The location of the battery- level indicator will vary depending on the model.
3) Knowing when the battery is about to run out means we can prepare for it, rather than
being cut off-guard when a device stops in the middle of a task.
4) Using battery-level indicator, gives an idea of how much battery power is being used when
working with a certain materials.
B. Disadvantages
Determining the charge remaining in many battery types not connected to a system that
monitors battery use is not reliably possible with a voltmeter. In battery types where EMF
remains approximately constant during discharge, but resistance increases, voltage across
battery terminals is not a good indicator of capacity. A meter such as an equivalent series
resistance meter (ESR meter) normally used for measuring the ESR of electrolytic capacitors
can be used to evaluate internal resistance (Elisa et al., 2021).
And there are some disadvantages of using the ESR meters
1) ESR meters fitted with protective diodes cannot be used, a battery will simply destroy the
diodes and damage itself.
2) An ESR meter known not to have diode protection will give a reading of internal
resistance for a rechargeable or non rechargeable battery of any size down to the smallest
button cells which gives an indication of the state of charge.
3) To use it, measurements on fully charged and fully discharged batteries of the same type
can be used to determine resistances associated with those states.
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4) The cost of an ESR meter makes it uneconomic for measuring battery voltages as its only
function, but a meter used for cheeking capacitors can take on the additional duty (McLamb,
2021).
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CHAPTER THREE
MATERIALS AND METHOD
3.1 Materials
S/N ITEM Qty
1 C1 33µF/35V CP_Radial_D10.0mm_P5.00mm 1
2 C2 0.1µF C_Disc_D3.0mm_W1.6mm_P2.50mm 1
3 R1 56KΩ R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal 1
4 R2 1.2KΩ R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal 1
5 D1 1N4001 D_DO-41_SOD81_P7.62mm_Horizontal 1
6 U1-LM3914 LM3914 DIP-18_W7.62mm 1
7 7 G-LED7, G-LED8, G-LED9, G-LED10, O-LED4, O-LED5, O-LED6, 10
R-LED1, R-LED2, R-LED3 LED LED_D5.0mm_Clear
8 RV1 200KΩPotentiometer_Bourns_3266W_Vertical 1
9 RV2 10KΩ Potentiometer_Bourns_3266W_Vertical 1
10 Power LED software
11 Wire
12 Soldering iron
13 Pliers
14 Screw drivers
15 J1 12V Battery TerminalBlock_Altech_AK300-2_P5.00mm 1
16 Resistor
17 Diode
18 Zener Diode
19 Potentiometer
20 Capacitor
21 Transistor
22 Transducer (Buzzer)
23 U1 lm 3914
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3.2 Procedure/ method
Indicator LEDs will be connected to the corresponding output pin of LM3914 IC. In this
circuit we will use 18 pin PDIP package IC. Bias to this IC directly applied from the input
battery. RV1 Variable Resistor controls sensitivity of signal input and RV2 – Variable
Resistor controls divider and Reference Adjust. In this Battery level indicator circuit dot
display single LM3914 driver configuration used hence the mode select pin (9) leaved as
open circuit. If you want to connect 20 LEDs then you can use two LM3914 ICs together.
In this circuit LEDs (D1-D10) displays the capacity of the battery in either dot mode or
display mode. This mode is selected by the external switch sw1 which is connected to 9th pin
of IC. 6th and 7th pins of IC are connected to the ground through a resistor. This resistor
controls the brightness of LEDs. Here resistor R3 and POT RV1 forms potential divider
circuit. Here pot RV1 is used for calibration. There is no need of any external power supply
to this circuit. The circuit is designed to monitor 10V- 5V DC. The circuit will work even if
the battery voltage is 3V. The operating voltage of this IC is 3v - 25v DC. Lm3914 drives
LEDs, and vacuum fluorescents. The IC contains adjustable reference and accurate 10-steps
divider. This IC can also acts as sequencer.
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Circuit Diagram
Fig. 3.1 Battery Level Indicator
16
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