Ovidiu Predescu's Weblog

How to build an Arduino project from the command line

For the projection screen controller I'm building I decided to use an Arduino hooked up to a GuruPlug. This way I offload the communication with the outside world to the GuruPlug, which runs a full Linux server, complete with Ethernet and WiFi connectivity. The Arduino is now used to control the motors and relays, and to receive input from an IR sensor, limit switches and infrared proximity sensors. This solution replaces the relatively cumbersome solution involving an Ethernet shield hooked up to the Arduino.. The software on the Arduino becomes a lot simpler too, without the Arduino TinyWebServer running on the Arduino board itself.

However it does have its own complications. Since the Arduino is now hooked up to a remote computer, I need to be able to build the C++ code for the Arduino on my host development machine (a MacOS X), push it to the GuruPlug running Linux and have the GuruPlug program the Arduino with the new binary.

The build process for the Arduino is handled internally by the Arduino IDE. The logic needed to build a typical Arduino project is hidden inside the Java program, which knows about the Arduino built-in libraries, as well as any additional user-defined libraries. I was hoping I could write a simple makefile to do the actual build, but the library dependencies are determined implicitly from the C header files included by your project's .pde file. It could be done using a combination of shell and awk, and a recursive invocation of make, but it's slightly more complicated. A major problem I hit was with file names containing spaces, which abound at least on MacOS X. Make uses a lot of built-in functions that use space as delimiter between the elements of a list, and it's impossible to use any built-in make functions.

Because of the space character problem, I gave up on make. I was looking for a build system that uses a more programatic approach, and so I found SCons. It's a nice build system built entirely in Python. I was about to write a build file for it when I found arscons, a small build file for Arduino-based projects. The funny thing is that the project was checked in Google Code only two weeks ago. Very timely indeed!

In classic open-source fashion - which I haven't done since I joined Google, back in 2003 - I made few improvements to the code and sent them to the author. I can now build my Arduino project on MacOS X, have it pushed to the GuruPlug and from there uploaded to the Arduino board connected to it.

Prerequisites

For this to work there are a few prerequisites for your development system. Make sure you have Python 2.5 or newer installed. Once you have Python installed, install SCons and the Python Serial module. On a Linux system you can install these by doing:

sudo apt-get install python2.5 python-serial scons

If you're on a Mac, you can get these slightly easier by installing MacPorts. If you do this, make sure you're running the python that comes with MacPorts, and not the default one in the MacOS X distribution. If you decide not to use MacPorts, download and install the packages manually, the process is pretty straightforward.

If you want to push the Arduino binary to a remote machine where the Arduino is connected, you also need to install the Python Fabric package on the host computer. On the remote computer (the GuruPlug in my case), you need to install Python Serial and avrdude. Again if your remote computer is a Linux box like the GuruPlug, you should be able to run apt-get to install the packages.

Once you have these packages installed, download the SConstruct file and put it in your Arduino project's directory. If you plan on remotely pushing the binary, download the pulsedtr.py file and place it in the same directory.

Building your Arduino project

After you install everything, you should be able to build your project using this command:

scons

This will only build the project. To build it and upload it to an Arduino connected to the same computer, run this:

scons upload

If you have a single Arduino board connected to your host computer, scons should be able to identify it automatically. If for some reason it doesn't, run scons like this:

scons ARDUINO_PORT=/dev/<arduino-tty-device> upload

If your Arduino board is not a Duemilanove, you might need to specify the board type using ARDUINO_BOARD. To see a list of possible values for this argument, run scons like this:

scons ARDUINO_BOARD=

Beside the parameters defined above, a few others can be defined in the command line:

• ARDUINO_HOME used to specify the location of your Arduino IDE package
• ARDUINO_VER the version of the Arduino IDE
• EXTRA_LIB if you have additional libraries that you'd like to use for the build, specify that directory using this argument.

For additional parameters that you can specify, look in the SConstruct file.

Deploying to an Arduino board connected to a remote computer

The most complex scenario is when you develop on a machine and push the binary to an Arduino connected to a remote computer (in my case that's a GuruPlug). This usually happens after the development phase, when you deploy your Arduino/GuruPlug project. At this point you don't want to take out the Arduino board from inside your project's box. This option allows you to reprogram the Arduino remotely, directly from your development machine.

To do this, you need to make sure you can login to the remote computer (GuruPlug in my case) using ssh without being asked for a password. You can do this by creating a new RSA key and placing the .pub key in the ~/.ssh/authorized_keys on the remote computer. Let's say your new key is in ~/.ssh/guruplug. You should be able to do this from your host computer, and be logged in to the remote machine automatically (obviously you need to replace user and remote-machine accordingly:

ssh -i ~/.ssh/guruplug user@remote-machine

You can now run scons and have it build, push the Arduino binary to the remote system, and upload the binary to the Arduino board connected to the remote system. Here's how:

scons REMOTE_HOST_STRING=user@remote-machine REMOTE_BOARD=atmega328 \
    REMOTE_TTY=/dev/ttyUSB0 SSH_KEY=~/.ssh/guruplug1 remote

Possible issues

I ran into a strange while trying to push the binary to the remote system using fabric. From the stack trace the error was inside paramiko, the library on which fabric is based. This problem was happening even after I created a new RSA key without a password. Each time I would run scons I got this error:

SSHException: invalid key

The error turned out to be inside ~/.ssh/known_hosts which apparently contained an invalid key, or a key paramiko couldn't parse properly. I removed all the suspect keys from it, and the error disappeared.

How to build a plastic box for a small project

I needed a small box to house some electronic boards for a remotely controlled projection screen project I'm building. The GuruPlug computer I'm using for the project has WiFi on board but no external antenna. A metal box would severely limit the radio waves, if not shield them completely, so I decided to go with a plastic box instead.

I couldn't find any plastic boxes that would fit my project, so I decided to build my own. Luckily there is a TAP Plastics store right in downtown Mountain View, and they carry a large selection of plastics. On their web site they have a lot of videos showing what can be done with plastics.

It turns out you can build a box using acrylic panels very easily. Acrylic is very easy to cut holes into and you can glue the panels of the box almost as easily as you can glue paper. Check out this video showing how.

Below is the finished plastic box. If you don't have the machines at home to cut the panels to length, you can have TAP Plastics cut the pieces for you. I just got a bunch of scrap plastic panels they had on sale for $1 a piece, cut them on my table saw, drilled the holes using a Dremel, and glued them together. The total cost for the box below was $2 (excluding the tools and the time used to build it :)

Pictures that document the building process of the box can be found in this Picasa album.

Here are few tips when building your own box:

• Draw a diagram of how everything fits together and make sure you take into account all dimensions, including the thickness of the panels.
• Measure everything using the metric system, the inches are too coarse grained to achieve a good precision.
• Before glueing make sure the pieces fit the way they're supposed to.
• Use eye and ear protection. Drilled plastic flies around and it's really hot, you don't want this nasty stuff to get into your eyes. The Dremel is loud and I prefer to maintain my hearing to listen to music.
• When cutting with a Dremel the right attachments will make your life a lot easier.

  	If you don't already own a Dremel, this Dremel kit has the basic tool plus a lot of goodies that you'll find useful later on.
  	The circle cutter attachment for cutting circles. If you have the Dremel kit above, this accessory is included in it.
  	The Dremel router attachement for cutting straight lines. The circle cutter attachment above has a little metal piece that allows you to cut straight lines with it as well. The router attachment however is much easier to move in a straight line while you push on it.

• Here are additional accessories I found very handy when building the box.

  	When gluing panels together at a 90° it's a lot easier to align and hold if you use an adjustable clamp like this.
  	If you cut the plastic yourself on a table saw, get a high quality blade for cutting plastic. With this blade I didn't need to route the edges of the plastic pieces I cut prior to gluing.

Panasonic LX5

Whoa, it looks like I missed a slew of new camera announcements. The one I'm particularly interested in is the announcement of the new Panasonic LX5 camera, the successor of the LX3. I own the LX3 and it's a really great camera, especially in low light.

The LX5 camera extends the zoom range to 90mm from 60mm, it is now 24-90mm f/2.0-3.3, versus the LX3 which had a 24-60mm f/2.0-f/2.8. Sensor size is the same but it's a brand new one which supposedly has an increased dynamic range and even less noise. It looks like the sensor changes will improve movies in low light, since the minimum illumination is as low as 3 lux in movie recording mode.

Another addition is the new AVCHD Lite recording format for movies, which allows longer movies to be shot. The movies are no longer limited to the maximum 2GB file size. I haven't heard about the AVCHD Lite version before, but I find AVCHD a pain to work with. At least on Mac, you can't see the movies by opening them in QuickTime, you need to convert them first using an editing program.

Overall it looks like the LX5 is a nice incremental improvement over the LX3. I can't wait to see some side-to-side image comparison of the two cameras. For my usage, I think the LX3 is good enough. I don't shoot movies that long using the camera, so the new movie recording format doesn't affect me. With a 16GB SDHC card, I have plenty of space to shoot movies and pictures for a whole day.

Judging by the performance of its predecessor, I heartedly recommend buying the LX5 camera. Its low light performance is astounding for a compact camera.

Here are some pictures I've taken at various concerts using the LX3.

Umphrey's McGee at the Warfield, San Francisco:

Arduino and GuruPlug

Few months ago I attempted to make an Arduino-based project accessible via a web browser and/or a phone using an Ethernet shield (see here and here). The results were a bit disappointing, as the Ethernet shield tends to behave strange when the files to be transferred are large. Everything seems to be fine if the file to be transferred is just below the Ethernet MTU (1492 bytes by default), with extremely fast transfers all the time. When the file exceeds that threshold, there are a bunch of inexplicable timeouts which make the file transfer to be seconds instead of milliseconds.

I then discovered the GuruPlug. For $100 you get a full computer running on a Marvell 1.2GHz processor, with 512MB RAM and 512MB flash as the hard drive, 1 Gigabit Ethernet, 802.11 b/g and 2 USB 2.0 ports! The best part is that the GuruPlug consumes less than 5W, so you can have it on at all times.

The company making the device is positioning the GuruPlug as a general purpose computer, but I think that's a mistake. I'm not going to trust such a puny computer to run my file server. However it's powerful enough to run a bunch of dedicated little applications. I've been running my home's internal DNS server for more than a year now on the previous generation SheevaPlug.

Since the GuruPlug has 2 USB ports and has both Ethernet and WiFi, you can easily connect it to an Arduino and have the web server run on GuruPlug, while having the actual interface with motors and sensors done by Arduino. The communication between the two can easily happen over USB using a custom made protocol. More on the software side of things in a different post

Since I want my project to go inside a single box, and not have lots of wires running around, I disassembled the GuruPlug and removed the main board. Doing so voids the warranty, so do this at your own risk! You need to provide 5V at 1A to the board. I removed the USB connectors on both the GuruPlug and the Arduino board, and ran some wires directly between them. This way I don't need to run a dedicated USB cable between the two boards. On the downside, I lost a USB port which could have been exposed outside of the box.

Right now I'm in the process of building a small box for the project. Since the GuguPlug doesn't have an external WiFi antenna, I needed to build the box from plastic instead of metal. Another thing to keep in mind is that the metal part that's on top of the GuruPlug board is a heat sink that runs very hot. I'll most likely put a fan right on top of it, even though the original GuruPlug doesn't have any. More on the building of the actual box in a later post.