(These tips are mostly identical for the JeeNode, JeeNode USB, and JeeLink)
FIRST-TIME POWER UP OF THE JN2 / JN3 / JN4 / JU2 / JL2
Do not plug the ATmega chip in yet (or remove it if you did so already).
Connect a 4.5 .. 6V power source to the board.
Check that the regulator (IC2) stays cold - if it gets warm, switch the power off immediately:
IC2 might be soldered on the wrong way around or you may have a short circuit. Fix it.
Now disconnect power and plug in the ATmega chip. If it came with the kit, then it has the bootloader and "RF12demo" already pre-loaded. If not, you'll need to use an ISP programmer to first program the bootloader into the microcontroller. This can be done through the SPI / ISP connector on the JeeNode.
INITIAL TEST
The first step is to hook up the JeeNode to the Arduino IDE via an FTDI cable of breakout board (such as the USB-BUB from Modern Device). This will supply power to the board and set up a serial connection.
If you don't have the Arduino IDE installed and working yet, do that first:
http://arduino.cc/en/Guide/HomePage
Launch the IDE and set the board type ("Arduino Duemilanove or Nano w/ ATmega328") and serial line from the Tools menu. Then launch the Serial Monitor (last button, after the three arrows) and set the baud rate to 57600. The moment you do, you should see the following text lines appear:
Available commands:
<nn> i - set node ID (standard node ids are 1..26)
(or enter an uppercase 'A'..'Z' to set id)
<n> b - set MHz band (4 = 433, 8 = 868, 9 = 915)
<nnn> g - set network group (RFM12 only allows 212)
<n> c - set collect mode (advanced, normally 0)
t - broadcast max-size test packet, with ack
...,<nn> a - send data packet to node <nn>, with ack
...,<nn> s - send data packet to node <nn>, no ack
<n> l - turn activity LED on PB1 on or off
Remote control commands:
<hchi>,<hclo>,<addr>,<cmd> f - FS20 command (868 MHz)
<addr>,<dev>,<on> k - KAKU command (433 MHz)
If you get this far then the main parts and microprocessor are working properly. Bravo!
TROUBLESHOOTING
If you didn't see the above text, then something is wrong. Is the power properly connected? Measure it with a volt meter or a LED + series resistor. Is the ATmega chip the right way around on the board? Any solder bridges which are causing trouble? Or perhaps a bad solder joint on one of the connections? Is the USB serial link properly connected? Is the serial monitor running with baud rate 57600? Did you select the correct serial port?
WIRELESS TEST
Once you have one JeeNode running, you can build a second one and test it in the same way. You'll need two JeeNodes powered on to perform a wireless radio test. Once both units pass the above intial test, you can take it a step further and try the wireless communication. This is described in the README:
http://jeelabs.org/view/libraries/RF12/examples/RF12demo/
Make sure to configure both JeeNodes for the same frequency band and net group. And make sure there is an antenna wire attached to the radio module, or you might not get any signal - even if the units are next to each other.
If all went well: congratulations, you're done!
If not, hop over to the forum at http://talk.jeelabs.net/ and look / read / ask - hopefully a solution is near...
NEXT STEPS
The Ports library offers a simple way to control the I/O pins on a JeeNode.
The RF12 driver can be used to control the wireless module.
For quick reference, you can print out the JeeNode pinout diagram.
Here's a good page to get started with wireless nodes: http://wiki.jeelabs.net/pof/71
Some notes about connecting external power: http://news.jeelabs.org/2009/12/07/jeenode-power-pins/