LITERATURE REVIEW
2.1 THEORY
The LM3914 is a monolithic integrated circuit that as well as a LED at the same time,so controller senses analog voltage levels and drives 10 LEDs, functions including “staging” control can be providing a linear analog display. A single pin performed. The LM3914 can also act as a changes the display from a moving dot to a bar programmer, or sequencer.
Current drive to the LEDs is regulated and The LM3914 is rated for operation from 00C+70oC. Programmable eliminating the need for resistors. The LM3914N-l is available in an 18-lead PDIP. This feature is one that allows operation of the whole system from less than 3V.
The circuit contains its own adjustable reference and accurate 10-step voltage divider. The low-bias-current input buffer accepts signals down to ground, or V-, oscillations. Yet needs no protection against inputs of 35V above or below ground. The buffer drives 10 individual comparators referenced to the precision divider. Indication non-linearity can thus be held typically to 1/2%, even over a wide temperature range.
Versatility was designed into the LM3914 so that controller, visual alarm, and expanded scale functions are easily added on to the display system. The circuit can drive LEDs of many colours, or low-current incandescent lamps. Many LM39l4s can be “chained to form displays of 20 to over 100 segments. Both ends of the voltage divider are externally available so that 2 drivers can be made into a zero-center meter.
The LM39 14 is very easy w apply as an analog meter circuit. A 1.2V full-scale meter requires only I resistor and a single 3V to 15V supply in addition to the 10 display LEDs. If the I resistor is a pot. it becomes the LED brightness control. The simplified block diagram illustrates this extremely simple external circuitry.
The LM3914 can also act as a programmer or sequencer. The circuit contains its own adjustable reference and accurate 10-step voltage divider The LM39I4N is available in an 18-lead molded package, Drives leds. LCDs or vacuums fluorescents .No multiplex switching or interaction between outputs Input operates down to ground. It has 10 step programmer and Multi-step or “staging” controller LED driver outputs are current regulated and open-
collectors.
The battery level indicator contains the driver IC as the main part of it. Every aspect is internally architecture as will be later shown via the internal block diagram of the driver IC.
Being the vital part, study of it is necessary.
The simplified LM3914 block diagram is to give the general idea of the circuits operation. A high input impedance buffer operates with signal from ground to 12V, and is protected against reverse and overvoltage signals. The signal is then applied to a series of 10 comparators: each of which is biased to a different comparison level by the resistor string.
In the example illustrated, the resistor string is connected to the internal 1.25 reference voltage. In this case for each 125mV that the input signal increases, a comparator will switch on another indicating led. This resistor divider can be connected between any two voltages, providing that they are 1.5 below V+ and no less then V-.if an expanded scale meter display is desired. The total divider voltage can be as little as 200mV.Expanded-scale meter displays arc more accurate and the segments light uniformly only if bar mode is used At 5OmV or more per step, dot mode is usable.
The reference is designed to be adjustable and develops a nominal 1.25V between the REF OUT (pin 7) and REF ADJ (pin 8) terminals. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current Il then flows through the output set resistors R2 giving an output voltage of:
VOUT=VREF(1+R1/R2) +IADJ. R2
Since the 1 2OuA current (max) from the adjustable terminal represents an error term, the reference was designed to minimize changes of this current with V+ and load changes. The voltage at pin 9 is sensed by comparator Cl. nominally referenced to (V+ to l00mV). The chip is in bar mode when pin 9 is above this 1evel otherwise it’s in dot mode. The comparator is designed so that pin 9 can be left open circuit for dot mode. taking into account comparator gain and variation in the l00mV reference level, pin 9 should be no more than 2OmV below V+ for bar mode and more than 200rnV below V+(or open Circuit) for dot mode. In most applications, pin 9 is either open (dot mode) or tied to V+ (bar mode). In bar mode pin 9 should be connected directly to pin 3. Large currents drawn from the power supply (LED current, for example) should not share this path so that large IR drops are avoided.
2.2 LITERATURE
COMPONENT USED:
2.3 REVIEW
The battery level indicator thus consists of IC LM3914, resistors, Light emitting diodes, switch. Combination of these components forms circuit which denotes the battery capacity.
The circuit consists of various resistors which is used to limit the current and also to decide the brightness of the LEDs. The variable resistor is connected to the IC LM3914 which forms the voltage divider network and it is used for calibration purpose. To run the circuit 12V power supply is provided. IC LM 3914 is the comparator IC. The IC runs at a voltage
range of 3-15V
The switch is connected to pin 9. If the pin 9 of IC is left free, it shows DOT mode display and if pin 9 is connected to positive supply, it shows BAR mode (AllLEDs remains lit).