Operating at 3.3V or 5V requires precise resistor values to avoid dropping too much voltage across the IC. 2. Updated LM3915 Resistor Calculator Formulas
electrolytic capacitor across the LED supply to ground to prevent oscillations. 4. Sourcing Your Components If you're starting a new project, the LM3915 IC Go to product viewer dialog for this item. is available from various electronic component retailers.
Using an updated calculator is a for hobbyists. It prevents the most common mistake: setting the reference voltage higher than the supply voltage (
The is a classic logarithmic display driver used to power LED bar graphs for audio levels and signal strength. While the original LM3915 datasheet from Texas Instruments (formerly National Semiconductor) provides the fundamental formulas, modern "updated" calculators make the design process much faster.
Let’s calculate components for a standard 12V VU meter with 10mA LED current and a maximum VRHIcap V sub cap R cap H cap I end-sub
Calculating the external resistor values (R1, R2) to set specific LED thresholds (e.g., -20dB to +6dB) is tedious. It requires solving logarithmic equations where one wrong decimal point ruins your entire prototype.
The LM3915 remains a classic choice for driving 10-segment LED bar graphs, especially for logarithmic audio or signal displays. However, calculating the external resistors (R1, R2) and mapping voltages to individual LEDs can be tedious.
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 equipment, signal level meters, and VU meters.
While many forums host static PDFs, the most powerful tool currently available is hosted on DIYStompboxes and ElectroSchematics (version 4.2 as of late 2024).
2.34−1=R2R12.34 minus 1 equals the fraction with numerator cap R sub 2 and denominator cap R sub 1 end-fraction
The calculator then provides a comprehensive set of values, including:
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is small, but an updated calculator must include it for precision. 2. LED Current ( ILEDcap I sub cap L cap E cap D end-sub
Since the LM3915 is a 3dB/step driver, the thresholds are not linear. If your VREFcap V sub cap R cap E cap F end-sub