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The LM3915 operates using an internal 1.25V reference between the (Pin 7) and REF ADJ (Pin 8) pins. The relationship between the resistors and the full-scale voltage ( VOUTcap V sub cap O cap U cap T end-sub ) is defined by the following equation:
Previous versions assumed perfect voltages. The updated calculators now include a drop-down for LED forward voltage (1.8V for Red, 3.2V for Blue/White) and account for the internal voltage drop of the IC. This means your calculated brightness will actually match reality.
You want a 10V range meter. You already calculated R1 as 1kΩ (for dimmer LEDs, ~1.25mA) for this example: lm3915 calculator updated
This quick-lookup table provides calculated resistor values for standard peak voltages, assuming a standard target LED current of approximately 10 mA to 12 mA ( Target Full-Scale Voltage ( VREFcap V sub cap R cap E cap F end-sub R1cap R sub 1 Calculated R2cap R sub 2 Nearest Standard R2cap R sub 2 Approximate ILEDcap I sub cap L cap E cap D end-sub 0 Ω (Wire Link) 2.5V 3.3V (Modern Logic) 5.0V 9.0V 12.0V Modern Design Considerations
This voltage sets the threshold for the 10th (highest) LED. It is programmed by the ratio of R1cap R sub 1 R2cap R sub 2 The LM3915 operates using an internal 1
If you don't want to do the math, use these common configurations for a standard supply: Target Full Scale ( VREFcap V sub cap R cap E cap F end-sub R1 (Program) ILEDcap I sub cap L cap E cap D end-sub 1.25V Ωcap omega Ωcap omega Direct Line Level 2.50V Ωcap omega Ωcap omega High-Output Audio 5.00V Ωcap omega Ωcap omega Standard Logic Level 10.0V Ωcap omega Ωcap omega 10V Log Display Blog Post: Building the Ultimate 30dB VU Meter 1. Mode Selection: Dot vs. Bar LM3915 Dot/Bar Display Driver - Mouser Electronics
The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, providing a logarithmic 3 dB/step analog display. It is widely used in audio engineering for VU meters, power indicators, and signal level monitoring. This means your calculated brightness will actually match
The calculator will suggest the nearest standard E24 resistor value: . Step 3: Calculate R2cap R sub 2 (Full-Scale Voltage) R1cap R sub 1 is set, input your desired full-scale reference voltage ( VREFcap V sub cap R cap E cap F end-sub