01 October 2008

Xbee Arduino Shield Kit

Yow. I've soldered a few things in my day but I kinda struggled putting together the NKC Electronics Freeduino Arduino Xbee Shield V2.0 Kit. Sure laugh it up, look at the very few parts in the picture. But this took me almost 3 hours of intensive labor, smelling caustic fumes, and burning fingers. I clearly over estimated my solder-foo.

The kit is great, well marked, pieces are minimal, the assembly instructions are clear, I just need practice soldering the many header pins. I'm so glad there wasn't any Surface Mount (SMT) because I couldn't have done it.

Now that it's built ... Now what? I need to interface this thing to the Pololu LV168 Orangutan Robot Controller. The shield is intended to work with an Arduino not an Orangutan. Both are based on the Atmel ATmega168 microcontroller but different form factor, different layout. Hmm ... Did I buy the wrong Xbee thing? Why was the shield thing the way to go? This click-to-buy option on web pages is starting to get me in trouble. I buy before I really know if it's the right solution. Hell, at least I got to practice my soldering skills.

The great thing about an Arduino shield is that it lines up with the sockets on the Arduino board and makes all the necessary electrical connection auto-magically.

The bad thing is that an Orangutan isn't the same form factor as an Arduino and that shield wasn't going to just line up and plug in. I need to connect the pins myself.

The best that I can tell, the Xbee really only needs 4 pins connected. Many other options but in the dirt simple mode, just these four:
  • +VCC
  • Ground
  • Din (Tx)
  • Dout (Rx)
The shield has a TLV2217 voltage regulator that takes the Orangutan's +5V and outputs a nice +3.3V for the Xbee. I knew that I wanted that shield for something. So, I need to power the shield with +5V but where? Where does the voltage get applied? Looking at the schematic, it was still not clear. The only place I see +5V is to the ICSP. Could that be it?

I posted a few forum questions at various boards and received the usual RTFM responses. Those are really helpful. I'm struggling, just have a question that I can't find the answer to anywhere, I really have read the flippin' manual and searched till I'm blue, and the experts don't help. Instead they write, "If you look at the pins on an arduino, you can see which pins get connected to what". Great, thanks much.

In the ICSP link above, the Tinker It Now dude says "connect the 5v only if you want your Arduino to power the target board". That was the first clue (thanks Tinker It Now) that I found about how a shield gets powered.

So I hook +5V to the shield's ICSP pin 2, GND to the shield's ICSP pin 6. Half way there.

What about Rx/Tx (Din/Dout)? What pins do they get hooked to? On an Arduino, digital pins 0/1 are Rx/Tx. Are they the same for an Orangutan? Pololu's excellent docs come to the rescue yet again. TTL-level communication are with pins PD0 (RX) and PD1 (TX).

But it can't be that easy, can it? After I hooked it up, I didn't seem to transmit. Something's wrong. Stupidity is what's wrong. Don't hook Rx to Rx and Tx to Tx. The Rx from Xbee goes to Tx on the Arduino/Orangutan. The Tx from Xbee goes to the Rx on the Arduino/Orangutan. That's better. Make the right connection and the damn thing works. Cool. What's next?

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