LM3914 Making Automotive Battery Detector ----- LM3914 Power Indicator

LM3914 is a point / bar display drive integrated circuit developed by NS Company. Contains input buffer, 10-level precision voltage comparator, 1.25V reference voltage source and point / bar display mode selection circuit, etc. The homogenous input terminal of the 10th-level voltage comparator is connected to the resistor divider, and the resistor voltage divider consists of 10 1kΩ precision resistance series, and the weight of the comparator is equal, and the 10-level linear display driver is constituted for LEDs. The linear scale device of the LCD, VFD) level meter can be driven. The operating voltage is 3V to 25V (up to 48V), the output current is adjusted at 2 to 30 mA, and the output terminal pressure is ± 35V, and the maximum output is limited to 30mA. The input buffer is in the form of follower and improves the input impedance and measurement accuracy. There is a hysteresis circuit inside the LM3914, which is displayed from one LED immediately jumps to a male LED, but is gentle, eliminating noise interference, improving the flashing phenomenon caused by the rapid change of the input signal. Since the internal resistance divider is floating, the voltage measurement range is wide. The drawings are a dynamic dot voltmeter of the exhibition, which can be used in the state of continuous measurement of the 12V battery. The LM3914 4, 6 feet are the low end and high ends of the 10-stage resistor divider, R2, RP2 are used to preset the output current of each voltage comparator, that is, the current through the LED1 to LED 10, this current is a reference reference voltage (1.25 V) 10 times the current supplied. For example, the RP2 is adjusted to the uppermost end, then the preset resistance is 1.2kΩ (R2), and the total resistance of 10kΩ with the inner divider is connected in parallel, 4, the equivalent resistance between 1.25V is 1.07KΩ, 1.25V reference reference voltage source The current provided is 1.25 V, 1.07kΩ ≈ 1.2 μA, and the current of each luminous tube is 1.2 mA × 10 = 12 mA. 7, 8 inside the inside is 1.25V reference voltage, due to R2, RP2 provides 2.50V ~ 3.75V DC basic measurement range, and the input signal is obtained by the positive power source R1, RP1. Therefore, the reading should be a basic amount by preset multiple. The display is red, green, two LEDs, when VCC is in the normal range of 12V to 14V, green LED illuminates; if VCC is 10V to 12V or 14V ~ 15V, the red LED illuminates. There is a logic control network inside the LM3914, and different signals are selected by the ⑨ foot, select the moving point display or strip display. When ⑨, (11) is connected to the moving point display mode; ⑨, 3 (VCC) foot is connected to the bar display mode. This table can be calibrated to this table after all components are installed and inspected. Methods as below: 1. The VCC is connected to 15.0V DC voltage. The RP1 is adjusted to illuminate the LED 10. 2. The VCC is connected to 10.0V DC voltage. The RP2 is adjusted to make the LED1 shine. 3. Repeatedly adjusted several times. This table can be connected to the 12V DC contact between the ground and the ignition switch. Author: Zhang Fengyi