Construction And Design Of Battery Level Indicator Circuit

Project and Seminar Material For Electrical Electronics Engineering EEE

Construction And Design Of Battery Level Indicator Circuit


Technology on batteries has advanced over the years as a result of the need to power portable devices that have risen in numbers in the last decade. Just like primary cells, rechargeable batteries work in the same way, only their chemical reactions are reversible. This project aimed at building a system that would indicate the capacity level of a Nickel Metal Hydride battery upon charging and discharging. The Nickel Metal Hydride battery was selected in this project due to its preference among consumers. However, since the principle behind the rechargeable battery technology is similar, the system can be used to test other types of batteries. System implementation involved designing and building a battery charger circuit and a discharge circuit. Software design then followed, after which testing was performed. The project uses a LM3914 driver IC use to drive 10 leds by passing through it sufficient amount of current. Brightness of leds are controlled by reference adjustable pin and reference out pin. The project goal was achieved and results were presented through numeric figures, charts and indicators. The system is expected to help in planning with batteries to avoid halt of devices during operation. The results gathered during testing point to possible reduced battery wastage. A better way to handle batteries to conserve capacity has also been highlighted.

Chapter One


1.1 Project Overview

Battery level indicator is a circuit that is used to check the battery life. We can easily recognize the battery level with the help of LED’s. It uses a LM3914 driver IC use to drive 10 leds by passing through it sufficient amount of current. Brightness of leds are controlled by reference adjustable pin and reference out pin. A variable resistor is also deployed in the circuit to have variable input voltage at pin 5 of the driver IC. Since the driver IC has two modes of operation which is bar graph mode and dot mode, it enables us to have indication of the battery life either in bar form or in dot form.

We can have coloured lods to indicate state of the batteries like first three leds will indicate low battery. Green leds will indicate full battery. Thus by using various coloured leds representation of battery life will be made easy to understand. Cascading the driver ICs we can increase the range of battery input in terms of voltage. In the below given block diagram we have 4 blocks. One is the power supply. other is the driver IC itself. We will have a led block and an input block. A reference input for comparison purpose. Leds will glow according to the input given and the reference Input present.

Power supply is ranging around 12 to 18V. Reference voltage is pre decided which is 1.25mV. Any dc signal lying in the range of the power supply is judged and the level is indicated by the leds. The current through the leds is controlled by the internal adjustment.

2 The battery level indicator consists of very less component and thus occupies very little space of the surrounding. Since only DC input voltage levels are indicated, components which work in AC supply can be used to detect AC levels. Since AC voltage having continuously varying amplitudes the leds will turn ON and OFF continuously making a good looking pattern. Thus our battery level indicator can be used for decoration purpose also.

1.2 Advantages

  1. A battery level indicator is with electronic appliances to arrange as to display, on an indicator, a real time voltage detected by voltage indicator.
  2. Indicator indicates how much power the battery will be able to supply to electronic apparatus.
  3. It is used to check the battery level with the help of LED’s for example if three LED’s, indicates battery capacity of  30 percent. And if 10 LED’s glow then it is 100 percent.
  4. Easily indicate the battery level
  5. Enhanced version of this circuitry is the present mobile phone battery level indication system
  6. This circuit can be used in household applications like INVERTER. This circuit connected to inverter can help the users to know when to charge and when to leave the inverter idle
  7. Minimized version of this circuit can be also used for automobiles to indicate the battery level and low cost.

1.3 Disadvantages

  1. In case of voltage matching, correct level wouldn’t be indicated
  2. 1f input voltage is higher than the calibrated voltage, for full scale input error will be shown.

1.4 Future Scope

This project can be further extended in a useful manner, The basic design of battery level indication using single IC LM39 14 can be further improved by adding display control function and alert mechanisms to enable the easy knowing of the battery level. Instead of using the LED’S and LED controller in this circuit using a microcontroller can enable battery level indication as in mobile phones.

Chapter Five

Summary, Conclusion and Recommendation

5.1 Summary

The goal of the project was to design and build a system that would indicate the battery capacity level. The project stressed the understanding of batteries’ behaviour to define the system’s operational parameters. Besides the study and design of circuits, important activities that are part of Embedded Engineering projects, like ordering components and performing tests before critical stages just to mention a few, were equally important in understanding the management aspect of engineering projects. Following the study on batteries, numerous recommendations surfaced, which are not only helpful to the users but to the manufacturers as well.

The outcome of the project, despite a few challenges, met the objective target but with room for improvement. The system is expected to help in planning with the batteries to avoid unnecessary malfunction of devices and avoid wastage by throwing away batteries which are still useful. Proper level indication through the use of led indicators brings more understanding of how different rates of charging and discharging affect batteries. The findings from the project encourage proper use of batteries, improved battery management and conservation of energy with the help of the system.

5.2 Conclusion

This project is mainly designed to cheek the battery level by using LED’s. Here the battery level is known by the color and number of LED’s glowing at a time. This circuit uses mainly IC LM3914 which is basically a LED controller to operate LEDs. Also this circuit employs a relay which depends on the LED’s glowing and connects to the charging circuitry as required.

5.3 Recommendations

Despite the good project outcome, there is room for a number of improvements to make the system not just better but one that can test more than one battery at a time. A better system would be one that analyses the battery capacity level based on the two processes without human interaction. Testing more than one battery at a time will not only save time but will make it easy for those working with numerous batteries improve efficiency. This would mark a major improvement on the system.

A close improvement on the circuits would also see trickle charging performed when the end of charge is reached to ensure full charge and a good charging history. This ensures that the battery test performed is based on proper regulation of the two processes, thereby limiting errors that may result from improper charging and bad history of battery charging and the discharging.

The circuit with adjustable charging and discharging rates offers the option to choose the time duration to spend on testing a battery. This can be barked with options of selecting the type of battery to test. The list for improvements can be endless but the few mentioned are among those that can be achieved without much change to the current system design and operation.

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