Wireless audio amplifier with digital signal processing

Glasba je prisotna povsod in je del nas vseh, zato si nas večina želi imeti zmogljiv prenosni predvajalnik glasbe. Izdelali smo brezžični dvo-kanalni mono ojačevalnik tipa D, ki bo krmilil doma narejen, baterijsko napajan prenosni zvočnik. Zvočnik ima dva gonilnika (dva posamezna zvočnika), en visokotonski in en nizkotonski gonilnik. Prenosni zvočniki v današnjem času niso nič posebnega, saj so zelo razširjeni in lahko dostopni. Cilj naloge je bil zato narediti nekaj svojega in unikatnega, kar smo dosegli s samostojno izdelavo uglašenega lesenega ohišja in ojačevalnika, na katerem lahko po lastni želji obdelujemo zvok, ter ga prilagodimo svojemu okusu. Brezžično povezljivost ojačevalnika smo dosegli z izbiro mikrokrmilnika ESP32, ki ima vgrajen Bluetooth. Poleg brezžične povezljivosti, mikrokrmilnik omogoča tudi implementacijo raznih digitalnih filtrov, s katerimi lahko dodatno obdelujemo zvok. Digitaliziran zvok, s pomočjo digitalno analognega pretvornika (DAC) pretvorimo v analogni signal, s katerim krmilimo dva integrirana ojačevalna vezja. Vsako ojačevalno vezje krmili svoj gonilnik, zato smo lahko z digitalno obdelavo pripravili signal, ki je prilagojen vsakemu gonilniku posebej. Na ta način smo dosegli višjo skupno moč ojačevalnika, boljši izkoristek, ter manjše število komponent. Vezje ima možnost priklopa analognega signala, zato smo dodali tudi analogno digitalni pretvornik (ADC). Oba pretvornika sta zunanji integrirani vezji, saj izbrani mikrokrmilnik ne vsebuje pretvornikov z dovolj visoko ločljivostjo. Programsko koda, ki smo jo razvili na mikrokrmilniku je zasnovana okoli primera za prenos zvoka preko Bluetooth povezave, ki ga je pripravil proizvajalec izbranega mikrokrmilnika. Celotno kodo smo napisali v programskem jeziku C v programskem okolju Visual Studio Code. Pri načrtovanju smo si pomagali s programskimi orodji za simulacije kot sta LTspice ter VituixCAD, ter na ta način pospešili razvoj. Končan izdelek je izpolnil vsa pričakovanja. Prestal je prve teste in se izkazal z zelo majhnim popačenjem pri efektivni izhodni moči 70 W na posamezen kanal. Obdelava signala na mikrokrmilniku se je izkazala za zelo uporabno, saj omogoča zelo preprosto obdelavo in prilagoditev signala, brez da bi potrebovali spreminjati komponente na vezju.Music is everywhere and is part of us all. Therefore, we all want to have a powerful portable speaker. We have built a two-channel, D-type wireless amplifier, which will drive a homemade, battery-powered portable speaker. The speaker has two drivers, a tweeter, and a woofer. Portable speakers are nothing special these days as they are widely available. The aim of the task was therefore to make something unique, which we achieved by designing and building a tuned wooden speaker enclosure and amplifier, on which we can digitally process the sound and adapt it to our taste. The amplifier’s wireless connectivity was achieved by choosing an ESP32 microcontroller that has built-in Bluetooth. In addition to wireless connectivity, the microcontroller also enables the implementation of various digital filters, which can be used to further process the sound. Digitized sound is converted into an analog signal with the help of a digital-to-analog converter (DAC), which is used to control two integrated amplifier circuits. Each amplifier circuit powers its own driver, which means that we can digitally adapt the signal to meet the specific characteristics of each driver. In this way, we needed fewer components on the circuit board and achieved higher output power and better efficiency. Besides the wireless connectivity, the amplifier board has also the possibility of connecting an analog signal to its input. For that purpose, we added the analog-to-digital converter (ADC). Both of the converters are external integrated circuits since the selected microcontroller does not have converters with a high enough resolution. The software code that we have developed on the microcontroller is designed around the example of transmitting sound via Bluetooth connection, prepared by the manufacturer of the selected microcontroller. The entire code was written in the C programming language using the Visual Studio Code programming environment. To speed up the development process we used simulating software tools like LTspice and VituixCAD. The finished product met all expectations. It has passed some initial tests, which showed that it has very low distortion at an output power of 70 WRMS per channel. Microcontroller signal processing has proven to be very useful, as it allows effortless signal adjustments without needing to change circuit components