This time I'll present you a project that I'm particularly proud of. Well, this is a bluetooth remote control for winamp. But it is not everything that it does, as you will see...
Well, let me explain you why I had this idea. Everytime I'm moving around my appartment, there are always things that I would like to do remotely when I'm listening to my music: change the volume, see what track is being played, move to the next track, and why not, stop the music and make a skype call using the remote.
This is the concept, if you haven't understood it let's put it another way:
As you can see on the picture, the microcontroller is connected to the computer using an USB link. This link will be used to charge the Li-Ion battery of the remote, reprogram the microcontroller using the provided bootloader. And since we have a USB connection, why not make the remote be recognized as an external multimedia keyboard? Why? So if you don't have a bluetooth adapter on your computer, you can still change songs when connected through USB ;).
A few words about the choice of components. For the uC, I chose an AT90USB1287 from Atmel, which will be running at 8Mhz, has 128kb of flash memory (used to store the LCD graphics), has an embedded USB bootloader, and whose compiler is free (WinAVR). For the Bluetooth chip, it was the LMX9838 which was pretty hard to get when I did this project, it is a Bluetooth to UART controller with embedded antenna. It can also control an audio codec, that's why I chose the Winbod W681310 which was one of the supported. Finally, for the LCD screen, I found a nokia 130*130 color LCD bought on sparkfun.
Thus, this is the new concept picture with the components:
On the picture you will see the different protocols used between the components. The packets sent to the Nokia LCD through the SPI bus are 9bits long and since the SPI bus controller of the AVR only handles 8bits packets, I had to generate the first bit by hand (command / data bit). The PCM communication between the LMX and the codec is completely handled by the BT chip, no need to worry. For the USB communication, that was a bit more complex to do since you have to send all the appropriate USB descriptors that the PC requests (interesting link here). Implementing a HID peripheral device was not that hard, however when you create a device having 2 HID descriptors (one for the multimedia keys and one for the arrows...), Windows recognizes it as a composite device and thus must have the appropriate driver to install it (wonderful huh?), the solution was to copy the HID descriptors, the vendor ID & product ID of an old multimedia keyboard I found.
Now let's have a look on our global project architecture from a layer point of view:
Here you can see what are the different layers used for the remote to work. I implemented a protocol to know which tracks are being played and to give orders to winamp, which is using a serial port over bluetooth. On the windows side it is very easy to use, you just have to write data into a port you opened, using normal C / C++ functions. On the other side, the LMX just output the data it received so the microcontroller has just to parse it. As usual, all the details / files are given at the end of this article. Here is a brief overview of the protocol (the packet fields are detailed in the source code):
Well, until now you just have seen general pictures, but nothing concrete I know... So let me show you the schematics and the PCB:
You'll notice that the board could be smaller. Why didn't I make it smaller? Because with this version you can produce it yourself, no need for big machines ;). Since a remote wouldn't be a remote without a packaging, let's design a small box:
Finally, let's produce the board & the box (yes, I can hear you say.... of course the first try wasn't completely successful, but here is the final result ;)):
Nice isn't it? Here is the picture of the remote communicating with winamp:
Yes, it displays the playing progression and you can browse through the winamp playlist. A button enables you to switch between player / menu mode where you can enable / disable several functions (power saving, USB keyboard...). Concerning the audio functionality, when pairing the remote, a headset profile is available on the remote. Thus, the remote can be used to make calls through skype or any voip software. It is worth mentionning that the winamp plugin I created will be also declared as a Skype plugin but because of the time I had left, I couldn't implement all the function calls to check if there was an incoming call / to call someone etc... (but however it is possible to do so when you see the plugin source code, you just have to communicate with the Skype API and add some new messages to the remote...)
Some final words about this project. I was really happy that in 3 months, working approx 16 hours a week I was able to create a project that was interfaced to a computer on such a high level (USB & BT). I've now a fully operational remote control for winamp that I can also use as a headset (2 jacks are on the board).
Here are all the files used / created for this project. PS: You'll see that the remote control source code is fully documented using doxygen and all the reports are in english
Bluetooth Remote Code Bluetooth Remote Schematics And Board Bluetooth Remote Final Presentation Bluetooth Remote Final Report (EN) Bluetooth Remote List Of Components Bluetooth Remote Datasheets BTP_Project_Utils.rar BTP_Winamp_Plugin.rar