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Most laptop PCs have an SDĬard reader slot, if not the TA has some USB adapters in the lab. The micro SD card comes with a larger SDĬard adapter and it should be inside the adapter in your kit. MBED COOKBOOK WAVEPLAYER WAV FILE CODEPlease use the constructorĬall in the below sample code that WRITES a simple message to a file on your SD card toĭetermine the pin connections that you need. The micro SD card () or a USB flash driveĬan be used for storage. Also the file to play needs toīe opened each time before playing and once it stops playing, it must be closed. MBED COOKBOOK WAVEPLAYER WAV FILE FULLPlay will need a prefix with the full path name (“/sd/myMusic/”). Note that C++ strings are stored aīit differently than C strings (no null character at end), but there is a function to convert them,Ĭ_str(), that can be found in the earlier filename example code. Style string variable as the argument for the filename to play. “sample.wav”) argument for the filename, this code will need a minor modification to accept a C The existing waveplayer hello world example code in main.cpp plays using a string constant (i.e. Mbed’s small internal flash drive is too slow for the wave player and the external SD card The clock might only work on some SD cards and the breadboard jumper wires would need to be SDFileSystem.cpp from 1Mhz to 20Mhz while reading the SD card file in the SDFileSystemĬlass and claims even higher sample rates, but it will work ‘as-is’ to at least 16Khz. An mbed user in Japan has increased the SPI clock frequency in The bottleneck that limits the sample rate is the read time of the SD card. MBED COOKBOOK WAVEPLAYER WAV FILE PCError messages are displayed with printfs to a PC terminalĪpplication window by the waveplayer code if you need to check them. The sample *.wav files can then be transferred to the micro SD card using a PC with print filename strings from vector using an iteratorįor(vector::iterator it=filenames.begin() it 20Khz?) and they can be resampled at a lower rate inĪudacity. read file names into vector of strings ……put this code somewhere in main, it assumes SD filesystem is setup…………… read all directory and file names in current directory into filename vectorįilenames.push_back(string(dirp->d_name)) Vector filenames //filenames are stored in a vector string It will need to be modified to display filenames individually on the This code shows how the filename stringsĬan be read into a vector. SD card file system is already setup in the program. Used to read the directory entries that makes the code relatively short. There is an existing C++ structure setup, dirent, that can be A sample code snippet is provided below that reads theįilenames from this directory into a C++ vector of strings and prints all of the filenames out to The player allows a user to select one of the files in the SD card’s myMusic directory to play Copy and paste can be usedįor entire C++ source files in the right column in the mbed compiler window. Over into the project, and the include statements for them will need to be added in main.cppĪlong with the code to setup and activate the pushbutton callbacks. Don’t forget the uLCD and PinDetect *.h and *.cpp files need to be copied Pushbutton and setup uLCD code from the earlier mbed lab and add it to the waveplayer Implementation files into your working directory. Skeleton code in previous labs you will need to copy over the appropriate header and In this lab you will need to add the micro SD cardįunctionality. It might be a good idea and save time to use the same pin assignments and breakout board Play on the LCD, play/stop, and adjust the volume using the pushbuttons. YourĪssignment will be to create and add a user interface that allows you to select which song to This code is already included in the waveplayer hello world example. This audio data sample buffer uses C style dynamic memory allocation with Is reading and buffering audio sample values to be sent later to the D/A from a *.wav format file Routine that outputs the next D/A value from a buffer and returns, while the wave player routine These timer interrupts periodically activate a fast interrupt In the wave_player class code used, a timer producing periodic interrupts (mbed Ticker API) is The speaker will notīe quite as loud using the D/A output as the earlier lab that used the PWM output to drive the Hello world program first to verify that the SD card and speaker hardware is setup correctly.ĭon’t forget that a “sample.wav” wave audio file is needed on the SD card. It would probably be a good idea to run the waveplayer Import the waveplayer hello world code example as your initial template. MBED COOKBOOK WAVEPLAYER WAV FILE DRIVERSD card using the speaker with the driver circuit connected to mbed’s D/A output described in There is an existing waveplayer hello world program that will play a wave file from the MBED COOKBOOK WAVEPLAYER WAV FILE PORTABLEIn this laboratory assignment, the mbed inventor’s kit parts will be used to build a portable music ECE 2036 Lab #4 - Build an mbed MP3 Player ![]()
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