In , if you are using a high supply voltage (e.g., 12V) and 20mA per LED, the chip can get very hot. The Fix: Drop the LED supply voltage ( VLEDcap V sub cap L cap E cap D end-sub
The formula is:
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). lm3915 calculator updated
What is the of the signal you are measuring?
You want a 10V range meter. You already calculated R1 as 1kΩ (for dimmer LEDs, ~1.25mA) for this example: In , if you are using a high supply voltage (e
VOUT=1.25×(1+R2R1)cap V sub cap O cap U cap T end-sub equals 1.25 cross open paren 1 plus the fraction with numerator cap R 2 and denominator cap R 1 end-fraction close paren
): The maximum peak analog voltage you want the 10th LED to represent (e.g., 5V or 10V). Target LED Current ( ILEDcap I sub cap L cap E cap D end-sub You want a 10V range meter
R1=12.5ILEDcap R sub 1 equals the fraction with numerator 12.5 and denominator cap I sub cap L cap E cap D end-sub end-fraction
R2=3×1200Ω=3600Ωcap R sub 2 equals 3 cross 1200 space cap omega equals 3600 space cap omega Closest standard E24 resistor value: . 4. Quick-Reference Lookup Table
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Old calculators gave you theoretical resistor values like 1,247Ω . A modern "updated" version has a dropdown to snap to (1.2k, 1.5k, 2.2k). It then recalculates the actual dB error (e.g., "Error: +0.2 dB @ step 7").