Whither Pi?

I’ve been aware of the Raspberry Pi for a while. (Despite the long stretches of inactivity on my blog, I don’t live under a rock.) However, until very recently I haven’t felt any particular need to have one.

That all changed in December. As with many families with younger kids, for us playing movies in the car is an essential component of longer car trips. Unfortunately, car DVD players are pretty horrible: unreliable, user-hostile, and just generally permeated with evil and crappiness. For a while I’ve been wanting a device that could play digital videos (i.e., DVD rips) in the car. Our kids are a bit young for tablets, and I’m not sold on the tablet concept in general. Another issue is display hardware: most inexpensive car LCDs take composite video input, but it’s not easy to find a device that does composite video output.

My realization in December was that the Raspberry Pi outputs composite video! Suddenly, I had to have one! The break between the Fall and Spring semesters is an excellent time to work on “fun” projects, so I started ordering hardware. My vision was a handheld device (containing the Raspberry Pi) that the parents in the front seat of the car would control, and which would drive the LCDs in the back seat via composite video. Audio output would feed into the aux input on the car stereo. All of the hassles of car DVD players would be eliminated: no interminable delay waiting for the disc menu, no skipping, no turning around to change discs, etc.

Building stuff

In pursuit of my vision, here is what I did over my break:

Learned how to use the Raspberry Pi: I used Raspbian, so I felt right at home, since my preferred Linux flavor is Debian/Ubuntu.
Learned how to use LibreCAD, specifically to design an enclosure (a durable outer casing to prevent fall apart) made with laser cut acrylic.
Learned about fbtft, a very nifty project to support small LCD displays as Linux framebuffers. I decided to use one based on the ILI9340 controller. These can be found on Ebay for about $6.
Designed a PCB using Eagle CAD for the pushbuttons that would serve as the mechanism for user input. I had originally thought about using a touchscreen, but they are somewhat tricky to interface with the Raspberry Pi, and this would have complicated the software I would need to write for the user interface. I actually designed two PCBs: the first one using standard 12mm x 12mm pushbuttons, and the second using Cherry MX keyswitches. The original pushbuttons felt extremely cheesy, and I also managed to orient the header connecting the board to the Raspberry Pi in a way that would have made the cabling difficult. Going with the Cherry MX switches worked out really well (see below!)
Accumulated massive quantities of parts and hardware from Ebay and other sources. This seems to be an inevitable feature of any hardware project.
Wrote a simple menu system using ncurses. Not only was this a lot easier than an actual GUI, it is less resource intensive, and it allows the LCD to be used as a debug console without the need for an external display or network connection: just plug in a USB keyboard and mouse.

You can read about all of the gory details in the build log if you’re interested.

All of the stuff I did is in a git repository (and, of course, is open source):

https://github.com/daveho/carpi

The weird thing I made

Anyway, here’s what I have so far:

Pretty cool, eh? Just to confirm what you’re probably thinking: it is really fun to press those keys.

What’s next

There are still two things I need to do in order to complete the project:

Finish the software: right now, it plays music, but playing video doesn’t work yet. I don’t anticipate that video will be too hard to get working, because omxplayer works fine from the command line, and my menu system just needs to run it as a subprocess.
Get all of the hardware installed in the car. I believe I have all of the parts I need. One annoying detail is that our 2007 base model Honda Fit didn’t come with an aux input for the car stereo, so we will need to have one installed.

I will update the blog when I have more progress to report.