Lm3915: Calculator

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

Example: For 20 mA (typical bright LED), ( R_\textset = 12.5 / 0.02 = 625 \ \Omega ). Use 620 Ω standard. Design goal: Audio level meter for -30 dBV to +6 dBV (36 dB range, but LM3915 only does 30 dB, so compress or shift). Desired: LED1 = -30 dBV, LED10 = 0 dBV (30 dB span). Reference voltage = 5.0 V (from 12V supply). LED current = 15 mA. LM3915 Calculator

[ \textAttenuation factor = \fracV_\textref,desiredV_\textmax ] 0 dBV = 1 Vrms → peak = 1

[ V_\textin,peak = \sqrt2 \times V_\textrms ] Use 620 Ω standard

[ V_\textRLO = V_\textLO - \text(offset) \quad \textand \quad V_\textRHI = V_\textRLO + \fracV_\textHI - V_\textLO10^(9/10) ]

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