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🔧 Basic LM3914 Connection Guide
1. Power Supply
Pin 3 (V+) → Connect to your supply voltage (typically +5V to +12V).
Pin 2 (GND) → Connect to ground.
2. Signal Input
Pin 5 (SIG IN) → Connect the analog voltage you want to measure (e.g., audio level, battery voltage).
Input range is defined by the reference voltage you set.
3. Reference Voltage Setup
Pin 7 (REF OUT) and Pin 8 (REF ADJ) form the internal reference.
Use a resistor divider between pin 7 and pin 8 to set the full-scale voltage.
Example: For a 0–5V display, configure resistors so REF OUT = 5V.
📌 Pin 7 (RHI) to GND via 470Ω
This sets the LED current using the internal reference voltage (typically 1.25V at Pin 8).
The formula for LED current is:
So with a 470Ω resistor:
This current flows through each LED when active — ideal for low-power applications.
📌 Pin 8 (REF ADJ) to GND
Grounding Pin 8 simplifies the reference setup.
It disables external adjustment and uses the default internal reference voltage (1.25V).
4. LED Outputs
Pins 10–18 → Connect to the cathodes of 10 LEDs.
LED anodes go to V+ (through a resistor if needed).
Each output sinks current, regulated internally (2–30 mA adjustable via pin 7 resistor).
5. Mode Selection
Pin 9 (MODE):
Leave open → Dot mode (only one LED lit at a time).
Tie to V+ → Bar mode (all LEDs up to the level lit).
6. Expansion
Multiple LM3914s can be cascaded for 20, 30, or more LEDs by chaining pin 10 of one IC to pin 11 of the next.
⚡ Example Applications
VU Meter: Connect audio signal (after rectification/filtering) to pin 5, LEDs show sound level.
Battery Level Indicator: Scale reference to battery voltage range (e.g., 10–15V), LEDs show charge status.
Voltmeter: Directly display 0–5V or 0–12V ranges with LEDs.
⚠️ Key Considerations
Current limiting: LM3914 regulates LED current, so external resistors are optional but can reduce power.
Accuracy: Reference resistor values determine scaling; use precision resistors for stable readings.
Supply voltage: Must be higher than LED forward voltage (e.g., ≥5V for red LEDs).
For, simple wiring diagram (showing pins, LEDs, and reference resistors) you can follow the LM3914 with LED bar graph circuit diagram below.
