Dual-Channel High-Performance RGB Audio VU Meter (Raspberry Pi Pico Based)

This project is a precision, dual-channel audio VU meter designed for professional audio environments such as mixers, studio equipment, DJ controllers, broadcast gear, and installation audio systems. It features 80 WS2812B addressable LEDs arranged in two 20-segment bargraphs per channel, delivering a bright and responsive real-time level display.

Balanced audio inputs are handled by a TI INA1650, providing high-CMRR differential-to-single-ended conversion with excellent noise immunity. The front end accepts balanced line-level signals up to +22 dBu (~10 Vrms) and produces clean, single-ended outputs suitable for the Pico’s ADC.

Each channel is conditioned through a low-noise audio ADC interface, including soft anti-alias filtering, source impedance control, and over-voltage protection. The Pico uses a dedicated filtered ADC reference rail for improved measurement stability.

An onboard rotary encoder with push-button allows software-controlled input sensitivity adjustment, ensuring optimal LED range whether the source is consumer (-10 dBV), professional (+4 dBu), or high-level line drivers. The bottom LEDs across both bars automatically indicate clip events by flashing white when the ADC approaches full scale.

The system is powered through a protected 24 V DC input using a JST-PH connector. Power filtering includes resettable fuse, TVS surge protection, reverse-polarity Schottky diode, and a π-filter (inductor + capacitors), ensuring a clean and stable 24 V rail for the INA1650 and the onboard 5 V supply for LEDs and logic.

The Raspberry Pi Pico handles real-time audio sampling, bargraph rendering, peak detection, gain control, thermal monitoring, and LED driving with smooth animation support.

📐 Technical Specifications

Input / Audio

• Balanced audio input (Left & Right), INA1650 front end

• Maximum input level: +22 dBu (~10 Vrms)

• Common-mode rejection: > 90 dB (typ.)

• AC-coupled and biased for single-supply operation

• Outputs: AUDIO_SE_L / AUDIO_SE_R, centered at mid-supply

ADC Interface

• Channels: ADC_L → GPIO26, ADC_R → GPIO27

• Input filtering:

  • 30 kΩ attenuation

  • 4.7 kΩ bias network

  • 1 nF RC anti-alias filters

• Schottky protection: ±3.3 V clamp using BAT54

• ADC reference: filtered 3.3 V (10 Ω + 100 nF + 1 µF)

LED System

• 80 × WS2812B LEDs, 5 V

• 4 bars: 20 segments each

• RGB color control per segment

• Clip indication uses bottom 4 LEDs per channel (WHITE)

Power Input

• Voltage: 24 V DC

• Connector: 6-pin JST-PH

• Protection:

  • Resettable fuse (PPTC)

  • 24 V TVS diode

  • Reverse-polarity Schottky

  • LC/π-filter

• Onboard 5 V 5A supply for logic and LEDs

• USB back-feed protection to prevent reverse powering

Microcontroller

• Raspberry Pi Pico

• Real-time sampling, LED driving, peak detection

• Internal thermal monitoring for optional brightness throttling

• Encoder interface with push-to-select

• Spare GPIO available for expansion

Controls

• EC11J-series rotary encoder with push button

• Adjustable software gain/sensitivity

• Push action displays current gain level on LED bars