Choose R1 = 1.2 kΩ. ( R2 = 1200 \times (5.0 / 1.25 - 1) = 1200 \times (4 - 1) = 3600 \ \Omega ) (3.6 kΩ).
[ \textAttenuation factor = \fracV_\textref,desiredV_\textmax ]
0 dBV = 1 Vrms → peak = 1.414 V. -30 dBV = 0.0316 Vrms → peak = 0.0447 V.
| Problem | Consequence | |---------|--------------| | Choosing R1/R2 for a specific full scale | Incorrect clipping level | | Converting dBu or dBV to required input voltage | Mismatch with line-level audio | | Setting RLO/RHI for offset display (e.g., -20 dB to +10 dB) | First LED never lights | | Resistor selection for precise 1 mA/LED | Burnout or dim display |
[ R2 = R1 \times \left( \fracV_\textref1.25 - 1 \right) ]
Choose R1 = 1.2 kΩ. ( R2 = 1200 \times (5.0 / 1.25 - 1) = 1200 \times (4 - 1) = 3600 \ \Omega ) (3.6 kΩ).
[ \textAttenuation factor = \fracV_\textref,desiredV_\textmax ] LM3915 Calculator
0 dBV = 1 Vrms → peak = 1.414 V. -30 dBV = 0.0316 Vrms → peak = 0.0447 V. Choose R1 = 1
| Problem | Consequence | |---------|--------------| | Choosing R1/R2 for a specific full scale | Incorrect clipping level | | Converting dBu or dBV to required input voltage | Mismatch with line-level audio | | Setting RLO/RHI for offset display (e.g., -20 dB to +10 dB) | First LED never lights | | Resistor selection for precise 1 mA/LED | Burnout or dim display | -30 dBV = 0
[ R2 = R1 \times \left( \fracV_\textref1.25 - 1 \right) ]
