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Led Voltmeter for Battery
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LED Voltmeter For Battery has as many as ten LED’s that are used to indicate the status of battery. This is a simple battery monitor used specially for car batteries. The battery voltage display is in the form of ten LEDs connected to the output of linear voltage display IC1. The voltage display range is from 7.5V to 14V. The lowermost LED D10 lights when battery voltage is 7.5V. The next LED D9 lights when battery voltage is at 8.2V. Thus with a span of each 0.7V, LEDs D10 to D1 glows sequentially or in dot mode by keeping switch S2 open. The uppermost LED D1 glows when battery voltage is at 14V. We can differentiate the glowing of each LEDs as a ‘battery status indicator’. The two lowest LEDs indicate ‘battery low’ condition. The next six LEDs indicate ‘battery well’ condition. And the uppermost two LEDs indicate ‘an overvoltage’ condition.We can show the display in bar mode also by making S2 on. In this case mode pin9 connected to supply line. At an overvoltage state i.e. when battery voltage range is 13 to 14V, all ten LEDs glows. As the voltage decreases LEDs turns off one by one sequentially.About the Circuit : The operation of the circuit is based on linear voltage display IC1, which consists of 11 op-amps as comparators connected internally. The input of IC1 is directly derived from the battery voltage via potential divider R4-R5-P1. This variable input is about 3V for battery potential of 12V. The display range depends on the internal voltage reference and resistors R1-R3. The reference output at pin7, which here is also the upper display level, is always 1.25V higher than the level at reference adjustment at pin8, so that the current from reference output to earth is about 1mA. The potential difference caused by this current across R2 and across R3 determines the lower display level. The lowest LED D10 lights when input voltage is 1.8V, whereas the uppermost LED lights when the voltage exceeds 4V. Since the input signal is divided by four, the display ranges should be multiplied by this figure. Therefore, the actual display range is 7.5-14V, which is 0.7V per LED when P1 is at minimum level.
