A 12V battery level indicator circuit using IC LM3914 is an important tool for checking how much power is left in batteries especially in devices that use 12V batteries.
It gives a clear visual display of how charged the battery is helping users take care of their batteries and avoid unexpected power cuts.
The IC LM3914 is a device that can detect different voltage levels and can control a display with 10 LEDs showing the information in either dot mode or bar mode.
This integrated circuit can work with a large range of supply voltages from 3 volts to 25 volts DC.
This circuit has ten LEDs that light up one after the other to show the voltage level, making it great for 12V lead-acid batteries or similar applications.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | 56k 1/4 Watt | 1 |
| 18k 1/4 Watt | 1 | |
| 4.7k 1/4 Watt | 1 | |
| Preset | 10k | 1 |
| Semiconductors | IC LM3914 | 1 |
| Switch | On/Off Switch for dot or bar mode | 1 |
| LEDs | Any 5mm, 20mA | 10 |
The LM3914 chip is used to show different voltage levels by lighting up a series of ten LEDs.
Depending on the input voltage these LEDs can work in two different ways: in DOT mode where only one LED lights up at a time or in BAR mode, where several LEDs can light up at once until a certain voltage is reached.
You can switch between these modes using pin 9 which is the mode selection pin.
When you press switch S1 pin 9 connects to the positive voltage turning on the bar graph mode.
If you do not press the switch pin 9 disconnects and the dot mode is activated instead.
To make sure the 12V input voltage is suitable for the IC1 LM3914s reference input a resistor divider made of resistors R1, VR1 and R3 is used.
The IC1 has an internal reference voltage at pin 7 that sets the voltage levels for when the LEDs will light up.
As the battery voltage changes the LEDs light up accordingly giving a clear and quick visual signal of the current voltage level.
Formulas:
Following formulas can be used for 12V Battery Level Indicator Circuit using IC LM3914:
Input Voltage Scaling:
The input voltage is scaled down to fit the LM3914s operating range.
Vscaled = Vinput × VR1 / R1 + VR1 + R3
where,
- Vscaled is applied to the LM3914 input
- V_input is the voltage from the battery 12V
- R1, VR1, R3 are resistors that create a proportional reduction of V_input.
LED Thresholds:
Each LED represents a fraction of the reference voltage:
VLEDn =n × VREF / 10
where,
- V_REF is the reference voltage set by the LM3914 pin 7 around 1.25V to 5V
- n is the position of the LED e.g. LED1, LED2 etc
- 10 is the total number of LEDs.
How to Build:
To build a 12V Battery Level Indicator Circuit using IC LM3914 follow the below mentioned connections steps to design your own circuit:
- Gather all the components as mentioned in the above circuit diagram.
- Connect pin 1 of IC1 LM3914 to cathode of LED1 and anode of LED1 to +12V DC
- Connect pin 2 of IC1 LM3914 to GND
- Connect pin 3 IC1 LM3914 with the positive supply of 12V DC of the circuit
- Connect pin 3 IC1 LM3914 to one end of resistor R1 and connect the other end of R1 to upper leg of preset VR1, center leg of VR1 to pin 5 pf IC1 and third leg of preset to GND.
- Connect pin 4 of IC1 LM3914 to GND through resistor R3.
- Connect pin 6 to pin 7 of IC1 LM3914 to GND through resistor R4
- Connect pin 8 of IC1 LM3914 to GND.
- Connect S1 switch between pin 9 IC1 LM3914 and 12V DC positive supply
- Connect pin 10 of IC1 LM3914 to cathode of LED10 and anode of LED10 to +12V DC
- Connect pin 11 of IC1 LM3914 to cathode of LED9 and anode of LED9 to +12V DC
- Connect pin 12 of IC1 LM3914 to cathode of LED8 and anode of LED8 to +12V DC
- Connect pin 13 of IC1 LM3914 to cathode of LED7 and anode of LED7 to +12V DC
- Connect pin 14 of IC1 LM3914 to cathode of LED6 and anode of LED6 to +12V DC
- Connect pin 15 of IC1 LM3914 to cathode of LED5 and anode of LED5 to +12V DC
- Connect pin 16 of IC1 LM3914 to cathode of LED4 and anode of LED4 to +12V DC
- Connect pin 17 of IC1 LM3914 to cathode of LED3 and anode of LED3 to +12V DC
- Connect pin 18 of IC1 LM3914 to cathode of LED2 and anode of LED2 to +12V DC
Conclusion:
The 12V Battery Level Indicator Circuit using IC LM3914 is a simple and efficient way to keep an eye on battery voltage.
The LED bar graph gives you a clear visual display, which is super helpful for devices that run on batteries.
This circuit is dependable, easy to build and does not need a lot of parts.
If you learn how it works and use the right formulas you can tweak the circuit to fit different voltage levels or uses.