Lm3915 Calculator – Extended & Confirmed

0 dBV = 1 Vrms → peak = 1.414 V. -30 dBV = 0.0316 Vrms → peak = 0.0447 V.

[ V_\textin,peak = \sqrt2 \times V_\textrms ]

But for simplicity, designers often set ( V_\textRLO = V_\textLO ) and ( V_\textRHI = V_\textref ) (if ( V_\textref ) is scaled to match highest LED threshold). More practically: The LM3915’s internal divider has a ratio of ~1.25 dB per step in voltage terms, so the voltage at step n is: LM3915 Calculator

[ R2 = R1 \times \left( \fracV_\textref1.25 - 1 \right) ]

Typically ( R1 = 1.2 \textk\Omega ) (recommended min). Example: To set ( V_\textref = 2.5 \textV ), ( R2 = 1200 \times (2.5/1.25 - 1) = 1200 \times 1 = 1.2 \textk\Omega ). If the lowest LED lights at ( V_\textin = V_\textLO ) and the highest at ( V_\textin = V_\textHI ), then: 0 dBV = 1 Vrms → peak = 1

[ \textAttenuation factor = \fracV_\textref,desiredV_\textmax ]

[ V_\textth,n = V_\textRLO \times 10^(n-1)/10 \times \fracV_\textRHIV_\textRLO \times 10^9/10 ] More practically: The LM3915’s internal divider has a

Then choose ( R_\textin1, R_\textin2 ) as a voltage divider. [ R_\textset = \frac12.5I_\textLED ]