VRHI=VREF×(1+R2R1)cap V sub cap R cap H cap I end-sub equals cap V sub cap R cap E cap F end-sub cross open paren 1 plus the fraction with numerator cap R sub 2 and denominator cap R sub 1 end-fraction close paren VREFcap V sub cap R cap E cap F end-sub is typically 1.25V. 3. Practical Example: 0V - 10V Logarithmic Input Let's design a 10V peak detector. Let (Excellent brightness). Calculate R2cap R sub 2 for 10V: resistor or a 10k pot for tuning). 4. 2026 Best Practices for LM3915 Projects LM3915 Dot/Bar Display Driver - Micro JPM
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 the "big brother" to the linear LM3914, making it ideal for audio level meters, power indicators, and signal strength monitors.
The LM3915 has a built-in adjustable voltage reference. It develops a nominal 1.25V reference voltage ( VOUTcap V sub OUT end-sub
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. lm3915 calculator updated
cap R 2 equals the fraction with numerator 5 minus 1.25 and denominator open paren 1.25 over 1200 end-fraction close paren plus 0.00008 end-fraction is approximately equal to 3.75 over 0.00112 end-fraction is approximately equal to 3348 cap omega standard resistor) 3. Select Display Mode (Pin 9) The LM3915 supports two visual modes: : Leave Pin 9 unconnected (floating) . Only one LED lights at a time. : Connect Pin 9 directly to . LEDs light up in a continuous "stack" or bar. Reference Values Table
at 0 dB), the internal comparator network activates the LEDs at the following precise input voltages: LED Number Percentage of VREFcap V sub cap R cap E cap F end-sub Voltage Threshold ( VINcap V sub cap I cap N end-sub LED 9 LED 8 LED 7 LED 6 LED 5 LED 4 LED 3 LED 2 LED 1 Critical Circuit Design Tips
If you are currently troubleshooting or prototyping a specific circuit configuration, tell me: What is your ? What is the maximum voltage of your input signal ? Are you running the display in Bar or Dot mode ? VRHI=VREF×(1+R2R1)cap V sub cap R cap H cap
In Bar mode, if the LED supply voltage ( VLEDcap V sub cap L cap E cap D 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.
), it can be ignored for most hobbyist calculations. The simplified formula is: Let (Excellent brightness)
When operating in Bar Mode with a high supply voltage (e.g., 12V), the LM3915 can become quite hot because it drops the excess voltage internally. To counter this, place a 10 Ω to 22 Ω power resistor in series with the LED anodes to drop some of the voltage safely outside the IC.
The LM3915 reads DC voltages at Pin 5. If you feed an AC audio signal directly into it, the display will flicker rapidly and look messy. For a clean audio VU meter effect, pass your audio signal through a simple precision rectifier circuit (using an op-amp and a diode) followed by an RC smoothing filter to extract the clean peak envelope of the music.
The new tools let you set custom Lower and Upper voltage ranges (e.g., 6V to 14V for a car battery) rather than just starting at 0V. This is the #1 requested feature that old calculators missed.