Welcome to the third instalment of Dive Into JeeNodes. Some real hardware now!
Both the remote sending side and the more nearby reeiving side of the wireless sensor link are handled by a JeeNode – which is essentially an Arduino-like microcontroller with some support circuitry, plus a low-power wireless radio module.
The JeeLink is a modified version of a JeeNode in a USB-stick form factor and enclosure.
But let’s start with that remote JeeNode first. What we’re going to set up is a little self-contained unit with a light sensor, a battery pack to power the whole thing, and the proper software pre-loaded onto the ATmega328 microcontroller inside that JeeNode.
The whole point of this “node” is that it’s completely autonomous. You’ll set it up once, take it to the place where you want to perform the light level measurements, hook up the battery pack, and that’s it. Its only task is to periodically measure the current light intensity, and report it over wireless – so that we can pick up the signal and pass it to the Raspberry Pi in a central location in the house, collect the data, tie it into the web server, and make it available on the local Ethernet network for visualisation in the browser.
Let’s set up that node now – except that it won’t be the final measurement code. Let’s start with a simpler goal first: sending out a counter value once a second, to see if we can pick up that value. With a little blink “blip” to let us know that the node is doing its work. But no light sensor for now…
As it so happens, JeeLib now includes an example sketch which does exactly that – see test1.ino on GitHub for the code (make sure you have the latest version of JeeLib!).
To get this code into the JeeNode, we need to communicate with it. This is done by connecting the JeeNode to our workstation / laptop – the one where we installed the Arduino IDE. That connection is created via a USB cable and “BUB”, as follows:
The next step is to tell the IDE which serial port to use to reach our JeeNode:
Go to the “Tools -> Serial Port” menu in the IDE, and select the serial port under which the USB BUB has registered itself. The actual name will depend on the platform (Windows, Mac OSX, or Linux) and in the case of Mac OSX, also on the unique name of that particular USB BUB.
Now, we need to load the proper sketch into the Arduino IDE:
Go to the “File -> Sketchbook -> libraries -> JeeLib -> DIJN -> test1″ menu. This will load the test sketch.
To check whether the code is in good shape, click on the leftmost round button with the checkmark in it (or go to the “Sketch => Verify / Compile” menu – same thing).
rf12_sendNow was recently added to JeeLib, make sure you’re using a recent version)
If all is well, you’ll get one line from the compiler, reporting something like:
Binary sketch size: 3,958 bytes (of a 32,256 byte maximum)
The value may differ a bit, but this indicates that the sketch is ok and can be uploaded.
The last step is where the real upload takes place, and since it includes the compile step, you could in fact have skipped that last instruction above.
Click on the second button from the left (the one with the arrow pointing right).
If all is well, you’ll see some LEDs blink the USB BUB, and when all is done a promising message “Done uploading.” will appear in the IDE (in the middle green bar).
If you get an error, make sure you have selected the proper board type (menu “Tools -> Board -> Arduino Uno”). Still no luck? Check that the USB serial port connection, the cable, the BUB, and the JeeNode are all hooked up as shown above. When in doubt, disconnect and reconnect gently.
Getting through this first upload is an important milestone. There are a few trouble spots, depending on the platform you use. You may have to install the latest FTDI USB driver. You may have to check that the serial USB drivers are present. There is not much generic advice to give here – other than “google for the error message you get”, in the hope that others have run into the same issue and that you’ll find a page with solution or tip.
At this point, you should see a brief LED flash once a second. This indicates that the JeeNode is running the test sketch and sending out its counter packet once a second.
Congratulations, you have set up a live test node for your wireless sensor network!
(This series of posts is also available from the Dive Into JeeNodes page on the Café wiki.)