Lm3915 Calculator -

A dedicated calculator solves these with direct equations. 4.1 Reference Voltage Divider (R1, R2) Given desired ( V_\textref ):

Then choose ( R_\textin1, R_\textin2 ) as a voltage divider. [ R_\textset = \frac12.5I_\textLED ] LM3915 Calculator

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: A dedicated calculator solves these with direct equations

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. Example: To set ( V_\textref = 2