STMicroelectronics AN2394 STR7/STR9 Audio Generation with PWM Application Note

This application note describes how to use PWM hardware to generate a .WAV audio file. It is targeted for STR7/STR9 microcontroller users.

Brand: STMicroelectronics
Category: microcontrollers
Document type: Application Note
Language: English
Pages: 13
File format: PDF
File size: 174 KB
Published: 07 August, 2012
Updated: 30 September, 2023
Models: STR7, STR9
MD5 checksum: 47167AB72278604D2AE2E9C884BF668F
PDF: STMicroelectronics AN2394 STR7/STR9 Audio Generation with PWM Application Note PDF

About this manual

This document describes a method for audio playback on STR7 and STR9 microcontrollers using Pulse Width Modulation (PWM) to simulate a Digital-to-Analog Converter (DAC). It details the requirements for .WAV file formats, specifically supporting PCM, 8-bit mono audio at sample rates of 8000, 11025, 22050, or 44100 Hz. The solution utilizes a system timer to manage data reading and a PWM timer to generate the analog signal, which is then filtered and amplified.

What's inside

WAV file format
Audio playback
STRx PWM description
Implementation example with STR711F
Hardware description
Firmware description
Revision history

Specifications

Supported Sample Rates	8000/11025/22050/44100 Hz
PWM Output Duty Cycle Range	0% to 100%
Recommended Low-Pass Filter Cutoff Frequency	4 kHz
Example Flash Memory	M25P64 (64-Mbit)
Example Audio Amplifier	TS4871

Frequently asked questions

How is the audio signal generated without an on-chip DAC?

The built-in Pulse Width Modulation (PWM) module is used to generate a signal whose pulse width is proportional to the amplitude of the sample data.

What is the recommended cutoff frequency for the low-pass filter?

The filter cut-off frequency is set to 4 kHz to ensure the PWM carrier is removed while passing the audio spectrum.

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