Many newer tools provide a "dB Table," showing exactly what voltage level triggers each of the 10 LEDs based on your chosen reference. The Math Behind the Tool
VREF≈1.25×(1+R2R1)cap V sub cap R cap E cap F end-sub is approximately equal to 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 2. LED Current Formula ( ILEDcap I sub cap L cap E cap D end-sub
VREF1.25=1+R2R1the fraction with numerator cap V sub cap R cap E cap F end-sub and denominator 1.25 end-fraction equals 1 plus the fraction with numerator cap R sub 2 and denominator cap R sub 1 end-fraction
LM3915 Calculator (updated version) is a specialized online tool designed to simplify the design of audio level indicators and VU meters using the LM3915 logarithmic display driver lm3915 calculator updated
To help tailor this design information to your specific electronics project, let me know: What ( VINcap V sub cap I cap N end-sub ) or audio source are you trying to measure? What color or forward voltage ( Vfcap V sub f ) are the LEDs you plan to use? Do you intend to run the display in Dot mode or Bar mode ? Share public link
Typically, the current is about the current flowing out of Pin 7. 2. Recommended Component Values LM3915 Dot/Bar Display Driver - Mouser Electronics
Type V+ = 12V . The tool checks if 2.0V < 10.5V (pass). Many newer tools provide a "dB Table," showing
Displaying logarithmic signal strength in radio receivers.
For decades, the LM3915 has been the undisputed champion of analog bar graph display drivers. Whether you are building a vintage VU meter for a hi-fi amplifier, a DIY audio spectrum analyzer, or a simple battery level indicator, this IC from Texas Instruments (originally National Semiconductor) has been a go-to component. However, one significant hurdle has always plagued engineers and hobbyists:
The chip's design, which has been in production since 1988, relies on a few external resistors to set its operating parameters. This is why a calculator is so useful—it saves designers from performing manual calculations for: What color or forward voltage ( Vfcap V
R2=1200×(5.01.25−1)cap R sub 2 equals 1200 cross open paren 5.0 over 1.25 end-fraction minus 1 close paren
If you are double-checking a calculator's results, here are the two "golden rules" of the LM3915: Common Value Typically 1.25V to 5V LED Current Usually 10mA ( Comparison: Manual vs. Updated Calculator
Because the internal 1.25V reference is multiplied: Vref = 1.25 * (1 + 1800/1200) = 3.125V . Then the step voltage ( Vref/10 ) is 0.3125V. Over 10 steps, this covers exactly 3.125V—which the tool scales to match your 1.875V audio window using the internal voltage divider at pin 5.
: If you require an exact voltage threshold (like exactly 5.00V), replace R2cap R sub 2 with a multi-turn precision trim potentiometer (e.g., a
The current drawn from the REF OUT pin determines the brightness of the LEDs. The internal circuitry mirrors approximately 10 times this current through each of the 10 LED outputs: