This project aims to create a Bluetooth speaker prototype using a Class D amplifier. The Class D amplifier operates with transistors in either saturated or blocked positions, minimizing losses and theoretically achieving a 100% efficiency.
- Introduction
- System Overview
- Signal Conditioning and Filtering
- Digital Processing
- Class D Amplifier Card
- Final Assembly and Testing
- Conclusion
The system converts the received audio signal into PWM (Pulse Width Modulation), which controls a power electronic switch. This switch increases the PWM voltage from 3.3-0V to 15-(-15)V. A low-pass filter then restores the amplified audio signal.
The Bluetooth module manages all Bluetooth-related actions, enabling connection with various devices like smartphones and computers.
The signal transmission process involves connecting the module via Bluetooth to the desired device, converting the received signal into an analog voltage signal.
The first step involves designing an electronic card to condition the stereo audio signal, ensuring optimal quality for further processing.
The audio signal from the Bluetooth module has values ranging from approximately -0.4V to 0.8V, which are not suitable for our processing system.
The signal must be adapted for the ADC (Analog-to-Digital Converter) of the DE10-Lite card, which samples values from 0V to 5V.
The circuit combines the stereo signals and adds a voltage offset to center the signal at 2.5V.
An operational amplifier (TL081) is used to amplify the signal, increasing its peak-to-peak amplitude for better sampling.
A low-pass filter is designed to ensure the purity and clarity of the final audio signal.
The ADC converts the analog input signal into a digital signal for PWM control.
The clock is divided to create the PWM period, and the comparator generates the PWM signal based on the ADC output.
A dynamic display on LEDs is created to visualize the signal amplitude.
An additional low-pass filter is implemented to modify the music, with a cutoff frequency of 1kHz.
The programs are tested using a function generator and an oscilloscope.
The Class D amplifier card uses a HIP4082 driver to control the H-bridge, which amplifies the PWM signal.
The final card is assembled and tested to ensure proper functioning.
The system is initially tested using a test platform, demonstrating clear sound output.
The complete system is assembled in a resonance box, with a 3D-printed speaker support and reclaimed wood for better sound resonance.
The project successfully demonstrates a functional Bluetooth speaker prototype with a Class D amplifier. Future improvements include adding a protection device for the 12V battery and integrating a volume control circuit.