Five skills of adding audio codec to embedded system

　　 The ability of embedded system to play audio is becoming a very common function . Audio provides users with good feedback , But now there are so many high fidelity audio available , Use beeps and chirps no longer to cut it . Developers can certainly use discrete components and DAC Get good audio from the system , But audio codecs have become very cheap , And it provides a wide range of functions for embedded developers , Otherwise, these functions will take time and cost to realize . In today's article , Let's study some techniques of adding audio codecs to embedded systems .

　　 skill #1 – Use microcontroller as master clock

　　 Audio codecs usually pass I2S(IC Inter voice ) Interface to the system . Many audio codecs provide developers with the flexibility of how to generate clocks for audio codecs . for example , The clock source can be passed by the microcontroller I2S The bus or oscillator connected to the codec generates . The codec itself can act as the master clock source and send the clock to the microcontroller . however , If developers want to minimize the BOM (BOM) cost , The simplest way is to set the microcontroller as the master and generate a clock for the codec . This minimizes costs and the number of components , And simplifies the audio playback system .

　　 skill #2 – Use an external audio amplifier

　　 Most audio codecs have built-in audio amplifiers . These amplifiers can usually output 0.5 To 1.5 Any power between watts , There are exceptions . If the audio application is simple and does not need a lot of output , Then use the internal amplifier to save BOM The cost is favorable . However , In most applications , Internal amplifiers cannot provide sufficient output power or flexibility for applications . For these reasons , Embedded developers often use external audio amplifiers , It can be adjusted through the speaker output system to obtain better performance . In these applications , The audio codec is usually set to bypass the internal audio amplifier , Because they usually expect to drive 4 or 8 Ohmic load . Then use the line output to drive the external audio amplifier .

　　 skill #3 – Use the audio block to adjust the speaker

　　 Many audio codecs are usually digital blocks . This digital audio module allows developers to carefully adjust their audio playback system for their applications . for example , A typical audio block may contain several programmable low-pass and high pass filters and a multipoint equalizer . These programmable components allow developers to carefully adjust their output systems , To maximize audio quality , At the same time, minimize the number of external components required by the system . The way these components are programmed depends on the frequency characteristics of the speakers used in the final application and the type of audio that will be used , For example, instrumental music and human voice .

　　 skill #4 – Store the codec configuration in a table

　　 The configuration of audio codec is usually through I2C Bus transmission , The digital audio stream passes I2S Interface transmission . Most audio codecs have dozens of registers , These registers need to be configured to make the codec run in the way required by the application , A good way for embedded developers to store this configuration information is to save the configuration table EEPROM Or flash memory , Then, during system initialization, the table is loaded into RAM in . then , If you need to adjust the system performance , For example, adjust the current volume , Users can modify RAM value . During initialization before enabling the audio playback system , Can pass I2C Send initial configuration , Then you can provide separate register updates as needed .

　　 skill #5 – stay PCB Add spare capacitor package on

　　 Capacitance is very important , Because sometimes the speaker needs to be pulled out “ A lot of ” Instantaneous energy , And capacitors act as energy storage . Capacitance is too small , Speakers may not move as needed , Therefore, there will be audio defects audible to the ear . The only way to ensure that there is enough is to measure while the system is running . No one wants to waste PCB Rotate to make sure there is enough capacitance , Therefore, a good practice is to set the capacitance as you expect , But add some additional parallel encapsulation , In case you need to adjust the required capacitance .

　　 Conclusion

　　 High fidelity audio is becoming the requirement of many systems , Because it provides users with audible feedback , Help them understand the state of the system . When the embedded development team first worked with the audio codec , They may feel afraid , But the truth is , They are not as bad as you first see from the data table .