![\"\"](\"https:\/\/lh3.googleusercontent.com\/-FvzM728uzLo\/UUYOb1hG-kI\/AAAAAAAAH0E\/c-jtuNIMGGo\/s1145\/20130317_192703.jpg\")
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In this post i will explain how I configured the PI to accomplish the task.<\/p>\n
<\/strong>What I used in this project?<\/strong><\/p>\n <\/strong>The idea<\/strong><\/p>\n The idea is to make a car radio capable of playing music from a usb pen plugged in the PI. My radio can only shuffle the songs found, but that’s just about software, it can be improved in many ways, that is where a lot of customization may take place.<\/p>\n Getting the display working with the PI<\/b><\/p>\n The first thing to do is to understand how to drive the LCD display from the PI. This is made by connecting the display to the PI’s GPIO, and then sending the commands from the programming language, usually using a library for the\u00a0HDD44780 standard.<\/p>\n I did this from python, but I won’t touch this part in this post because I followed a nice tutorial about this from Adafruit<\/a>.<\/span><\/p>\n After I was able to write to the display, I wrote a little python script to print something to the display from the command line, which could be useful to write something to the lcd from a shell script later:<\/p>\n Playing music through USB speakers<\/strong><\/p>\n To play music through a USB device, the PI must be configured properly. In my case, I had some operation to do before everything worked, and my speakers are still showing some problems when playing from the PI (I hear a little noise, but i didn’t search enough to tell it can’t be resolved).<\/p>\n Anyway, if you want to use your PI as a car radio, you probably want the USB speakers to be the default audio device for it. You can do this by editing the\u00a0\/etc\/modprobe.d\/alsabase.conf<\/em> adding the following line, or modifying the relative line if it already exists with another value (which in raspbian should be the case):<\/p>\n options snd-usb-audio index=0<\/p><\/blockquote>\n I had also another problem which seemed to be quite common, and I also had to add another line at the end of that file, to avoid an “expected delay” error which I discovered running\u00a0dmesg<\/em>:<\/p>\n options snd-usb-audio nrpacks=3<\/p><\/blockquote>\n I choose the higher value which didn’t give me errors in the log. After modifying the file i restarted alsa with<\/p>\n sudo service alsa-utils restart<\/p><\/blockquote>\n This wasn’t enough to play music through the speakers, I also had to specify the right device when i played the music with\u00a0mplayer<\/em>. I had to discover the name of the device running the following command:<\/p>\n aplay -L<\/p><\/blockquote>\n which gives a list of the recognized devices, from which i selected the right one, and finally got mplayer to play some mp3s:<\/p>\n mplayer -ao alsa:device=front my_music_file.mp3<\/p><\/blockquote>\n Usb automount and autoplay<\/strong><\/p>\n Now that the display is working correctly and we can play music through the speakers, let’s figure out how to handle the mounting\/umounting actions:<\/span><\/p>\n The next step is to configure the PI to automatically mount any usb drive plugged in. This can be done by using the <\/span>usbmount\u00a0<\/em>software avaiable in the raspbian repository:<\/span><\/p>\n sudo apt-get install usbmount<\/p><\/blockquote>\n Now, I want to autoplay music when the usb is plugged in, so I add a custom script to the default usbmount script folder\u00a0\/etc\/usbmount\/mount.d\u00a0<\/em>:<\/p>\n The first command uses the python script I created before to print something to the LCD when music is starting, while the third line starts the playback.<\/p>\n As you can guess, the $UM_MOUNTPOINT variable contains the path to the mounted drive.<\/em><\/p>\n The -slave<\/em>\u00a0mplayer option is a very useful way to let you send commands to mplayer even if it’s backgrounded. It tells mplayer to read input commands from a file, but if we provide a\u00a0fifo\u00a0<\/em>file instead of a normal one, mplayer will read from it only when we will write something. This allows mplayer to be controlled by writing to a file, from python, shell or whatever you prefer. To create a fifo file you should use<\/p>\n mkfifo \/home\/pi\/fifofile<\/p><\/blockquote>\n If you want to know more on the -slave<\/em> option of mplayer, see here<\/a>.<\/p>\n I had to add the\u00a0sudo -u pi<\/em>\u00a0part because it seemed that the user of usbmount wasn’t allowed to read from the fifo, I don’t know exactly why.<\/p>\n Finally, I also created a script for the umount event, which simply killed mplayer, and placed it in the\u00a0\/etc\/usbmount\/umount.d<\/em> directory:<\/p>\n\n
\n#!\/usr\/bin\/python
\nfrom Adafruit_CharLCD import Adafruit_CharLCD
\nimport sys
\nlcd = Adafruit_CharLCD()
\nlcd.begin(16,1)
\nlcd.clear()
\nlcd.message(sys.argv[1])
\n<\/code><\/p>\n
\n#!\/bin\/bash
\npython \/home\/pi\/lcd\/char\/print.py \"Madre foca:
\nPlaying music..\"
\nsudo -u pi mplayer -slave -input file=\/home\/pi\/fifofile -ao alsa:device=front -shuffle $UM_MOUNTPOINT\/* $UM_MOUNTPOINT\/*\/* $UM_MOUNTPOINT\/*\/*\/*
\n<\/code><\/p>\n
\n#!\/bin\/bash
\npython \/home\/pi\/lcd\/char\/print.py \"Music stopped.
\nI'm a super PI.\"
\nkillall mplayer
\n<\/code><\/p>\n
![\"20130318_214714\"](\"http:\/\/www.nicassio.it\/daniele\/blog\/wp-content\/uploads\/2013\/03\/20130318_214714-e1363639912560-225x300.jpg\")
<\/a><\/p>\n![\"\"](\"https:\/\/lh6.googleusercontent.com\/-baAwETMPko8\/UUeHwlfJjfI\/AAAAAAAAH18\/vpmVDZJzpRI\/s1145\/20130318_222855.jpg\")
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