Follow these steps to calculate the exact resistor values for your specific project requirements. Step 1: Establish Your Desired LED Current
The LM3915 is a monolithic IC that drives 10 LEDs, bar or dot display driver with a programmable gain. Here's a Python implementation of a calculator to help you design and calculate the required components for your LM3915 circuit.
To design your circuit using these updated calculations, follow these steps: 1. Determine Desired LED Brightness Choose your target current per LED (typically 10 m cap A 20 m cap A ). Calculate cap I sub cap L cap E cap D end-sub 10 m cap A 0.01 cap A ) brightness:
R2=3⋅1200 Ω=3600 Ω (3.6kΩ)cap R sub 2 equals 3 center dot 1200 space cap omega equals 3600 space cap omega space open paren 3.6 k cap omega close paren A 3.6k Ωcap omega lm3915 calculator updated
4.6 Microcontroller Integration (Optional)
R2=1200×3=3600 Ωcap R sub 2 equals 1200 cross 3 equals 3600 space cap omega Select a standard resistor. Logarithmic Step Thresholds (3 dB/Step)
For more information on the LM3915 and the calculator tool, visit our website or consult the following resources: Follow these steps to calculate the exact resistor
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
Note: To fine-tune the range, replace R2 with a potentiometer or a trimmer resistor.
| Desired Max Voltage | R1 (Brightness) | R2 (Range) | | :--- | :--- | :--- | | | 1.2kΩ | 0Ω (Direct to GND) | | 5V Range | 1.2kΩ | 3.6kΩ | | 10V Range | 1.2kΩ | 8.2kΩ | | 12V Range | 1.2kΩ | 10kΩ | To design your circuit using these updated calculations,
(12V−2V)×0.1A=1Wopen paren 12 V minus 2 V close paren cross 0.1 A equals 1 W This exceeds the package rating. Keep LED supply voltage ( VLEDcap V sub cap L cap E cap D end-sub ) as close to the LED forward voltage as possible ( is optimal). Always place a tantalum or electrolytic capacitor between Pin 2 (
If you do not want to run manual math, use this pre-calculated table using standard E24 resistor values for a target ILEDcap I sub cap L cap E cap D end-sub Desired Peak Voltage ( VMAXcap V sub cap M cap A cap X end-sub R1cap R sub 1 R2cap R sub 2 Actual Peak Voltage (Wire Link) 2.50V 3.30V 5.00V 10.00V 12.00V 5. Logarithmic Scale vs. LM3914 Ensure you are using the correct chip for your application. LM3915 (Logarithmic): Steps down in 3dB increments (
For this example, let's assume we want a standard line-level audio peak of . Thus, Step 4: Calculate R2cap R sub 2 Now we rearrange the reference voltage formula to solve for R2cap R sub 2 . To ensure maximum accuracy, we will factor in the typical IADJcap I sub cap A cap D cap J end-sub value of 75 µA (
The fixes all of this.