Lm3915 Calculator Updated [2021]

This feature ensures uniform brightness across all LEDs regardless of fluctuations in the supply voltage ( V+cap V raised to the positive power Updated Step-by-Step Design Workflow

The analog audio or DC voltage input signal.

VREF=1.25×(1+R2R1)+(IADJ×R2)cap V sub cap R cap E cap F end-sub equals 1.25 cross open paren 1 plus the fraction with numerator cap R sub 2 and denominator cap R sub 1 end-fraction close paren plus open paren cap I sub cap A cap D cap J end-sub cross cap R sub 2 close paren Note: The adjustment pin current ( IADJcap I sub cap A cap D cap J end-sub lm3915 calculator updated

The original LM3915 datasheet provides a brilliant solution for logarithmic display (1 dB/step over a 30 dB range). But the formula for the Reference Voltage (Vref) is intimidating to beginners:

Leave Pin 11 open-circuit for Dot Mode (only one LED lights at a time, conserving massive amounts of power). Connect Pin 11 to Pin 3 ( ) for Bar Mode (stacked display). Power Dissipation Warning: In Bar Mode, if and all 10 LEDs are on at This feature ensures uniform brightness across all LEDs

The LM3915 is not a linear driver; it is logarithmic. This makes it perfect for audio, where human hearing perceives sound pressure in a log scale, but it complicates the resistor math. To get the LEDs to light up at specific decibel levels, you have to calculate three critical reference voltages:

below . If your supply is higher (e.g., 12V), use a dropping resistor in series with the LEDs to prevent the IC from overheating, especially in Bar Mode. Mode Selection (Pin 9) : Bar Mode : Connect Pin 9 directly to Pin 3 ( Dot Mode : Leave Pin 9 floating (open circuit). Input Protection : While the IC can withstand ±35Vplus or minus 35 cap V , adding a Connect Pin 11 to Pin 3 ( ) for Bar Mode (stacked display)

You want a 10V range meter. You already calculated R1 as 1kΩ (for dimmer LEDs, ~1.25mA) for this example:

The LM3915 remains a classic choice for driving 10-segment LED bar graphs, especially for logarithmic audio or signal displays. However, calculating the external resistors (R1, R2) and mapping voltages to individual LEDs can be tedious.