12V battery level indicating circuit

MOS Power IC Full Range

Photocoupler

LM3914

The core of the circuit is derived from the LM3914, a versatile chip developed by National Semiconductor. The LM3914 is designed to sense voltage levels and display them through LEDs, operating in either dot mode (10-point) or bar mode. These modes can be combined by cascading multiple ICs for extended displays, starting with the first stage. It operates within a broad supply voltage range (3V to 25V DC), and its LED brightness can be adjusted using an external resistor. Additionally, the LED output is compatible with TTL and CMOS standards.

Description

In the circuit diagram provided, LED D1’s position (dot or bar mode) indicates the battery’s voltage level. The brightness of the LEDs is controlled via resistor R4, which connects pins 6 and 7 to ground. The combination of resistors R1 and R2 forms a voltage divider network that can be calibrated using potentiometer R2.

This particular circuit is designed to monitor voltage levels between 10.5V and 15V DC. To calibrate it, connect a 12V DC power source and adjust the 10K potentiometer until LED10 lights up (in dot mode) or glows as a bar. Lower the sensitivity further to ensure that LED1 only illuminates when the voltage reaches 10.5V. Switch S1 allows toggling between dot mode and bar mode. When closed, it connects pin 9 to the positive supply, enabling bar mode; when open, it disconnects pin 9, switching to dot mode.

A modified version of this circuit can be adapted to monitor different voltage ranges. Simply remove resistor R3 and connect the input directly to the upper layer. Adjust potentiometer R2 until LED10 illuminates (dot mode), then lower the voltage threshold by removing the lower level setting. Connect a high-value potentiometer (e.g., 500K) in place of R3 and fine-tune it until LED1 lights up. Once set, measure the DC resistance and replace R3 with a fixed resistor of the same value. The horizontal display is now calibrated.

Battery Diagram Using the LM3914 Circuit

Battery Indicator Circuit Using LM3914

Cascading Two LM3914 Chips

Two or more LM3914 chips can be cascaded to create an extended display. Below is an example of two LM3914 ICs cascaded together to form a 20-LED voltage level indicator:

Cascading Two LM3914

Other Related Battery Level Circuits You Might Find Useful

1. Simple Battery Level Indicator: This circuit monitors a 3V battery and uses the Panasonic MN13811G, a CMOS voltage sensor. When the LED D1 flashes, it means the battery voltage has dropped below 2.4V.

2. 3-LED Battery Level Indicator: This circuit uses three LEDs to indicate the voltage levels of a 12V car battery. The LEDs light up at 11.5V, 13.5V, and above 13.5V, respectively.

3. Flashing Battery Monitor: This circuit monitors 6 to 12V batteries and uses a transistor-based design to flash the LED by adjusting the voltage level with a potentiometer.