is set to , the LEDs will trigger at these approximate levels: -27 dB: 0.45V -24 dB: 0.63V -21 dB: 0.89V -18 dB: 1.26V -15 dB: 1.78V -12 dB: 2.51V -9 dB: 3.55V -6 dB: 5.01V -3 dB: 7.08V 0 dB: 10.0V
For years, the go-to tool for calculating LM3915 resistor values was a small, portable Windows application simply called "LM3915 Calculator." Released in 2012 by Elliott Sound Products, this freeware utility was highly valued for its simplicity and efficiency.
The current driving each individual LED is directly proportional to the current drawn out of Pin 7. The LM3915 regulates the LED brightness to approximately 10 times the current passing through R1cap R sub 1 lm3915 calculator updated
The top LED lights up too early. Calculator Fix: You forgot the 200Ω resistor between pin 5 and your input signal. The calculator now includes a mandatory "Input Buffer" recommendation. If your source impedance is high (>10kΩ), the calculator suggests adding an LM358 op-amp buffer before the LM3915.
For most common projects, you can simply use the table below. This assumes a standard LED current of roughly . is set to , the LEDs will trigger
R1=12.50.010 A=1250 Ωcap R sub 1 equals the fraction with numerator 12.5 and denominator 0.010 A end-fraction equals 1250 space cap omega Select a or standard E24 resistor. Let's use ( ), which adjusts our actual ILEDcap I sub cap L cap E cap D end-sub Step 2: Calculate R2cap R sub 2 for Target Reference Voltage
The LM3915 illuminates the 10th LED when the input voltage at Pin 5 reaches the full reference voltage ( VREFcap V sub cap R cap E cap F end-sub ). Therefore, set VREFcap V sub cap R cap E cap F end-sub equal to your maximum expected audio or signal voltage. Calculator Fix: You forgot the 200Ω resistor between
The LM3915 is a legendary chip. For decades, it has been the go-to solution for anyone building audio level meters, battery monitors, or any project requiring a visual representation of a logarithmic signal. While newer microcontrollers offer customizable displays, the LM3915 remains popular for its simplicity—it requires no coding and drives 10 LEDs directly with a beautiful logarithmic decay.
VREF=1.25×(1+R2R1)+(IADJ×R2)cap V sub cap R cap E cap F end-sub equals 1.25 cross open paren 1 plus the fraction with numerator cap R sub 2 and denominator cap R sub 1 end-fraction close paren plus open paren cap I sub cap A cap D cap J end-sub cross cap R sub 2 close paren IADJcap I sub cap A cap D cap J end-sub is typically very small ( ) and can be ignored for standard hobbyist calculations. Equation 2: LED Current Programming ( ILEDcap I sub cap L cap E cap D end-sub
Suppose you want to design a VU meter where the 10th LED lights up exactly at an input signal of , and you want each LED to draw 10mA of current for optimal brightness. Step 1: Calculate R1cap R sub 1 Using the LED current formula, rearrange it to solve for R1cap R sub 1