How to fix SL4A webCamFacade exception

On some phones, if you try starting the webcam using SL4A, you will get the following exception:

java.lang.RuntimeException: setParameters failed


Thankfully, the fix is simple. I found Paola Garcia‘s solution everywhere I looked on the internet. She was cheerfully answering everyone’s questions all over the place. She said she fixed the problem by changing the preview format from JPEG to NV21:


Thanks Paola!

But while the fix is simple, the hard part is you have to build a new SL4A app (APK) with the fix. Good news! It’s not really that hard because someone was kind enough to leave instructions. It was a good learning experience for me.

First, follow the first 2/3rds of this post:
Do only the “compile” steps. The last “how to package your app” part doesn’t really apply to you, since you just want to build SL4A.

I’m writing this post because I ran into some problems using the instructions above. I’m sharing my solutions in case anyone else runs into them too. I think most of the problems are because the post was written in 2011, and the latest libraries and SDKs in 2014 don’t play as nicely together.

The step you’ll want to substitute is when you Import your project source code. Instead of the “official” SL4A, Use hg to clone the SL4A repository from Paola Garcia‘s branch:

hg clone

(FYI: I used Tortoise Hg on Windows.)

Now here are the problems I ran into and how I fixed them. (Just in case anyone else runs into them too.)

  1. Missing Android SDK files when compiling
    SL4A needs APIs from the older Android SDK platforms. Check C:\Users\yourname\AppData\Local\Android\sdk\platforms. If you’re missing the directories android-3, android-4, android-7, android-8, you need to download/install them.

    In Eclipse: Window -> Android SDK Manager. Select all the Android SDKs til API Level 8 (Android 2.2).

    Download & install

    Download & install

  2. conversion to dalvik format failed with error 1
    I got this when trying to export the APK after compiling. I couldn’t figure out what the problem was for a while because stupid Eclipse just gave me the error message with no console logs. I finally found the problem when I did “Project -> Run As…” It gave me a helpful error message I could debug. Something about the JDK libraries was conflicting. I made two changes:

    Download JDK 1.6.0_26 and select it here

    Download JDK 1.6.0_26 and select it here

    Drop the Java compiler to 1.6

    Drop the Java compiler to 1.6

  3. Export APK
    I’m an Android noob so this step tripped me up too.
    Export signed package

    Export a signed package. Create a new keystore. I filled in blanks with B.S. and set passwords to “android”.

Finally, out pops your fresh APK with WebCamFacade fixed. Transfer the APK to your phone, uninstall the old SL4A app and install this new one.

Happy hacking! If these instructions were helpful, leave a comment below. Let us know what silly things you used your camera for. I know I have my eye on OpenCV 🙂

LG Optimus Dynamic – perfect cellbot phone?

It is the cheapest, full-featured Android phone that I’ve found. Only $20 on Amazon NEW. It feels like finding hidden treasure because the only reason it’s so cheap is that the phone is targeted for the bottom market. And, normal people who buy the phone later add minutes to use it as a phone. But not us! If everyone did what we want to do with the phone, they’d lose money because there’s no way this package can be produced and sold for a profit at $20. So shhhh… let’s just keep this between you and me.

Here’s what you do after you get it:

  1. (optional) Root it. That link takes you to a super simple one-click script and all you need is a PC and the USB cable that came with the phone. I don’t know why I rooted mine, but it’s Android and you can, so why not? You could install this custom ROM too if you want (I didn’t). And if you screw something up like I did, you always go back to “stock” with this.
  2. Install SL4A — the Scripting Layer for Android. This lets you interface with Android and everything your phone’s hardware allows… from a Python script.
    * Install the APK
    * Menu > view > interpreters
    * Menu > add > Python
    * Install the Python APK > OPEN the Python app > Install Python (+ whatever modules you want, like pySerial + pyBluez)

  3. In SL4A, go to Menu > view > interpreters > Menu > start server
    (Note the IP address and port, e.g.

  4. From your PC, write a simple Python script called to talk to the server on your phone:

  5. Notice the “import android” above. That’s from here. Download and put it next to above.
  6. python
  7. CHEER

The hardware isn’t great and it’s still on Gingerbread, but I’m pretty sure it’s still more powerful than NASA’s Lunar Lander. It’s just a steal at $20 for the nice package. Battery life is super and everything works fine. It even has an external micro SD slot! Oh one thing you might want to upgrade for our example above is the Text-to-Speech voice. Gingerbread is old so you don’t get Google’s latest TTS software. So I downloaded IVONA. It’s free, it works for Gingerbread and I like Amy’s UK English voice.

By the way, the SL4A website taught me that I’m not the first brilliant person to think of using smartphones for robots. And, the term for robots that use smartphones is Cellbots. But it still makes me wonder why people still want to mess with things like a $30 XBee WiFi module. Especially when phones like the Optimus Dynamic gives you WiFi (plus everything else) for $20. Who knows.

Happy Hacking!

PC to android smartphone recipe

Bao has been taking a break. I think having a robot that moves on its own stresses you out. You’ve been running to flip the off switch after playing with Bao a little. Maybe it’s too much for a 3 year old to deal with. On the plus side, now you know the deal with batteries and recharging, and how Bao gets slow when he’s low on energy. The “energy” and “battery” concept is handy for explaining why you have to eat and sleep.

Anyway, while Bao has been resting, we’ve moved on to the next phase of Bao’s evolution. After some research, I’ve found the perfect recipe. But first, check out the ingredients to see if you can guess what we’re making:

1) LG Optimus Dynamic
This is a $20 prepaid smartphone. Prepaid meaning you can actually buy minutes to use it as a smartphone (e.g. if you need a spare phone for family visiting from out of town). And this one’s nice because it has “triple minutes” for life. So you can buy 200 minutes and the phone will give you 600 minutes magically. But what I’m really buying this for is the hardware and software. It comes packed with the usual sensors: GPS, accelerometer, compass, light sensor; and communication interfaces: Bluetooth, WiFi, PLUS a camera, video recorder, audio recorder, a 1GHz processor, some RAM and 4GB of storage space, AND whatever apps you want and the Android OS to tie it all together. All for $20! In the robot world, each of these devices would cost $20 or more by themselves. But thanks to the economics of smartphones, you can get them ALL for $20. What a wonderful time we live in. I really feel that smartphone tech will accelerate many more industries. (Example: Oculus Rift.) So instead of buying loosey goosey electronics for your robo, the only thing you need is Bluetooth… to pair with a smartphone.

2) Scripting Layer for Android (SL4A)
This is what you install on your Android phone. SL4A lets you tap into every function on your phone from your favorite scripting language (e.g., Python). SL4A can either run a script stored on the phone, or you can connect to SL4A to run a script from your PC. E.g., check this out:

From your PC:

This tells your phone at to, "Capture what I say, then say it back to me." How crazy is that? (Browse the API to see what else it can do.) You can tell it to take a picture, make a phone call, or even drive a robot... (hint hint)

3) web2py
This is what I used to make a toddler-proof web interface or "app" or GUI. The front-end (View) is HTML/Javascript, and the backend (Controller) is Python -- perfect for hooking up with SL4A. Right now, it doesn't do much. But it still has you rolling on the floor laughing, because I send the words you type to the phone and the phone says them (using SL4A). You've been having fun typing different words to see how the text-to-speech voice screws it up. Anyway, this bomb-proof custom toddler web UI works much better than VI, which we were using earlier...

Oh, and here's my latest IR + Ultrasonic car code. It's tuned for the 3-wheel car and my kitchen: