Channels ▼

Al Williams

Dr. Dobb's Bloggers

Leonardo's Code

June 07, 2013

If you know me at all, you know I have an ongoing love/hate relationship with Arduino. I like that it has launched a whole ecosystem of inexpensive and readily available peripherals. I don't like the clunky IDE, the bizarre terms (like sketch), and the fan boy culture surrounding it. Perhaps part of what I don't like is the lack of innovation. At the core, the Arduino is nothing more than an Atmel chip, a bootloader, and the GNU C compiler. There's also a very simple (and hardly necessary) C language framework and a truly bad Java-based IDE that's only good feature is the way it integrates libraries (well, until you look at how it does it under the covers, but that's another topic).

More Insights

White Papers

More >>

Reports

More >>

Webcasts

More >>

All that applies to the traditional Arduino. However, I recently picked up an Arduino Leonardo board. It still suffers from the horrible IDE (and I talked about how to avoid the IDE before). It does, however, add something very powerful. USB support.

It is true that some Arduino boards — maybe even most — have a USB port. But that USB port essentially was a serial-to-USB adapter built on the board, not an integral part of the Arduino. The Leonardo's USB port is a real USB port accessible by the CPU. It still looks like a serial port for downloading and debugging your software. It can also look like a keyboard or a mouse! It can even look like all three devices at the same time.

As usual, the Arduino provides a clean library that's easy to use, so building an alternate keyboard or mouse becomes drop-dead simple. I've talked about building HID devices before and it wasn't that simple. Actually, it wasn't simple at all.

In the past, when I've used an Arduino it has been because they are readily available, but it wouldn't be my first choice for a project. However, if I were building a custom HID device, I would not hesitate for a second to select the Leonardo (or a similar USB-integrated Arduino). The ease of use is amazing.

How easy it is? Here's how to send Dr. Dobb's to your PC as though it were typed from the keyboard. This is the function that drives the sensor board (you can also download the entire file):

Keyboard.begin();
Keyboard.print("Dr. Dobb's");
Keyboard.end();

If you need to press modifier keys, you can use Keyboard.press and Keyboard.release, so the system is pretty flexible. The mouse is just as easy to use.

Compare that to how much code it takes to stand up an HID device without using a library (and yes, I know there are other libraries). In addition, having the serial port through the same line for debugging is very convenient (although, if you were writing a serious HID device, you might want to use the second serial port for printing debugging messages).

So what were the three things I learned?

1. How to get the IDE to work on Linux

The Leonardo's serial port shows up on Linux as /dev/ttyACMx (where x is some number like 0 or 1). That didn't throw me, but the IDE couldn't find it. I had read that the IDE actually figures out where the board is by putting the board through a reset. Because the serial port is software running on the Leonardo, the port disappears and then reappears. The IDE assumes any port that suddenly appears is probably the Leonardo and downloads to it. I just couldn't get this to work at all.

I tried to download the latest Arduino IDE but it still couldn't see the ACM port. I know the Java-based Arduino IDE uses the RXTX library for serial ports, so I tried removing the ones that come with the Arduino IDE and let the software use my default ones. That didn't work.

It turns out, you really do need to use the supplied RXTX libraries. You also need to modify the arduino executable (don't worry; it is just a shell script). The very last line is a Java command line that starts the actual IDE. You need to add –Dgnu.io.rxtx.SerialPorts=/dev/ttyACM0 to the arguments on that line (of course, use the right number if your Leonardo doesn't show up as port 0). While you are there, you might take out the swing option that sets the GTK look and feel — I hear some machines run the IDE faster without that option, although I didn't notice much difference.

2. !Serial really waits for the PC to open the port, not just connect.

Because the serial port disappears on every reset, it is common to see Leonardo programs use this idiom to wait for the serial port:

while (!Serial); 

This doesn't hurt anything on other Arduinos, so you see it in a lot of example code. I always thought this code would just wait for the serial port enumeration to complete (which takes a fair amount of time, by the way). However, it actually waits for something to open the port on the PC. So if you don't open the serial monitor, this will hang your program forever.

In the past, I've peppered my code with serial output statements for debugging and just left them in when I was done. You can still do that, but you better comment out that while statement, or your program won't run without an open terminal on the Leonardo's com port.

3. The IDE doesn't save before it compiles.

I actually ran into this before, but it bit me again this week. If the IDE crashes, any unsaved changes you made are gone. That might seem obvious, but most IDEs I've used save your code on each compile. So the most you lose is what you've done since the last build. The Arduino IDE does not do this. If you never saved your code then you'll get an empty file after a crash no matter how many times you've built your project.

Of course, the IDE has to save your code somewhere. It actually mixes it in with a bunch of other things and saves it in a temporary directory. In my case, I found the code in /tmp/build6606660780136176668.tmp (you can do a directory listing in /tmp sorted by date and find the most likely candidates). My program was called ranger, so the ranger.cpp file had my code in it, interspersed with extra stuff added by the IDE (#include and #line directives, mostly). It just took a minute to remove the extra lines and recover my file. Another reason I don't care for the IDE.

What could you do with the USB capability of the Leonardo? A host of custom keyboard ideas come to mind. Foot pedals for common input sequences. A detector that sends keys when an infrared beam breaks, or a temperature is too hot. Sure, you don't need to do this through a keyboard, but (as you'll see next time) you don't need any software on the computer to make it work. Most computers have some way to translate keystrokes into actions (AutoHotKey on Windows, for example; many different ways on Linux either built-in or using something like xdotool). So starting a video, for example, when someone breaks an infrared beam should require no custom software on the PC at all. It is easy to imagine a Leonardo and an accelerometer becoming a customized mouse. Again, the PC already knows how to read the mouse input, so you don't need any special software.

Next time, I'll show you a quick project that uses a cheap ultrasonic sensor and makes use of these ideas. I still won't say I'm a rabid Arduino fan, but I'm getting a lot of ideas related to custom HID devices that take minutes to create instead of days.

Related Reading






Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

 
Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.
 

Comments:

ubm_techweb_disqus_sso_-e7026b2453824be5e0212e054cedae10
2014-01-18T02:56:57

The main reason for the strange terms is that the people who already know how to do the things that aurdino and its followers are doing is that those who know are to snotty nose to teach those who dont know using simple terms that the average joe can understand ,where is a easy to understand book teaching java xxxxx that any 12 year old kid with no background in programing can understand ...years ago the kind of crap you people are writing was called job security and once all of you idiots retire then your nightmare will be over...WCH


Permalink
ubm_techweb_disqus_sso_-109f5c5e8eecf04eeb4ed7dfdbe0eca3
2013-06-18T15:05:19

Yes you have written some very nice articles but mainly focused on Linux and none cover the Visual Studio plugin which provides a very complete Arduino development tool for windows users. Keep up the good work and we hope to see Arduino on windows as the focus of a future article.


Permalink
ubm_techweb_disqus_sso_-b51f7a869a1175412e56da18be4810cb
2013-06-14T23:14:51

Thanks for the links. I have written before about how to use Eclipse and a few other options for Arduino, especially on Linux.


Permalink
ubm_techweb_disqus_sso_-109f5c5e8eecf04eeb4ed7dfdbe0eca3
2013-06-12T19:56:32

Windows users have the option to use Atmel Studio IDE and the Visual Micro plugin for Arduino. Atmel Studio is free and created by the manufacturer of the Arduino micro-controller, it is based on Visual Studio and is very mature. The Visual Micro plugin also provides an Arduino USB debugger. http://www.visualmicro.com


Permalink
ubm_techweb_disqus_sso_-ab14ca0cdf7f7bfadb8329c45d8b341d
2013-06-11T21:04:50

Sketch isn't any worse than script. It's just a term, but one familiar to artists. Guess who the Arduino was developed for ....


Permalink


Video