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Battery-level indicator

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    BATTERY-LEVEL INDICATOR 

    ANIRUDDH K.S


    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.

    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.

    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.

    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.

    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 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.

    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.

    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.

    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.

    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
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    Post Comment | 12 Comments



    Faizan   798 days ago

    If i want to use this circuit for a lithium ion battery 4.2V then what changes are to be made.Can the IC works on 4.2Volts power supply
    Reply   1 Reply
    Vasanthan.EEE   791 days ago

    it can operator even below 3VRefer httpwww.national.commpfLMLM3914.html#Overview
    Reply  
    Chetan M.P   691 days ago

    What changes Ive to make for 9 volt battery. Thank you
    Reply  
    Vinod   599 days ago

    Hicircuit is good but there is no need of 33k in base of transistor. It should be 5.6k. And the D1 will drop .6v so avoid that.
    Reply  
    udaya ghimire   579 days ago

    can i check this circuit diagram for 100 amp battery..
    Reply  
    kiranperva   477 days ago

    can we use 6V4.5AH battery?
    Reply   1 Reply
    Efy Admin   420 days ago

    Circuit was designed for 12V battery
    Reply  
    Prantik   451 days ago

    What are the advantages of this project?
    Reply  
    James   429 days ago

    can this work with a common cell phone?
    Reply  
    Sai   291 days ago

    how does the battery get charged as D1 prevents current to flow to battery?
    Reply   1 Reply
    Jagadeesh   262 days ago

    Only the charger ac source is connected through this circuit....the charger output is directly connected to the battery
    Reply   1 Reply
    md mahabubur rahman   228 days ago

    hw iclm3914 can work
    Reply  
    umashankar   179 days ago

    But This Circuit is not working properly.Is this want any changes to do?
    Reply  

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