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Battery-level indicator

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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.