LM3914 Based Battery Voltage Monitor
This voltage monitor is made to display the voltage of 12v battery (for UPS) on LEDs. For this purpose LM3914 is used. The voltage range decided to display is 10v to 13.5v for 12v battery. LM3914 is display driver that can be used in dot mode or in bar mode; dot mode , with only one led is lit at a time, and in bar mode where it lights leds progressively when the voltage increases. The circuit needs to be powered from the battery being measured and to be able to adjust the lower and upper voltages that light the first and last leds on the led bar. For the 12V battery, the first led in the bar will lit at 10V and the last one at 13.5V , giving 0.35V per led. These thresholds may be set to other values by adjusting two trimmers in the circuit. Calculation and Adjustments: Current flowing per led is controlled by R3 resistor, by applying ohm's law Ir3 =1.25v/ 4.7kohm =266uA. Where 1.25v is the minimum voltage required to operate the led. To be able to read the supply vo...