{"id":748,"date":"2010-06-21T04:33:07","date_gmt":"2010-06-21T08:33:07","guid":{"rendered":"http:\/\/www.etotheipiplusone.net\/?p=748"},"modified":"2010-07-05T04:40:50","modified_gmt":"2010-07-05T08:40:50","slug":"deathblades-the-birds-and-the-xbees","status":"publish","type":"post","link":"https:\/\/www.etotheipiplusone.net\/?p=748","title":{"rendered":"Deathblades: The Birds and the XBees"},"content":{"rendered":"

I’ve been waiting to use that title for a long time.<\/p>\n

Building the ‘blades has been quite an exercise in unfamiliar territory. First, the skates will be using the Maxon DEC modules<\/a>, which are essentially experimental with respect to the project, me having seen no other vehicles that use them (seriously – all other Google results seem to just be press releases). Having access to the DEC modules was the impetus behind me finally learning PCB design and layout<\/a>.\u00a0 I just discovered the magic that is force-sensing resistors<\/a> and how they can be used as an analog throttle.<\/p>\n

And now, as the final and pivotal step in closing the proverbial control loop of the Deathblades, I shall link the throttle with the DECs using XBee radio modules.<\/p>\n

\"\"<\/p>\n

SOOOOOO CUUUUUUUUTE. It’s just like a really obese centipede with a silly hat! That transmits and receives data!<\/em><\/p>\n

These little 2.4GHz, 802.15.4<\/a> radio modules are very popular in the DIY and maker crowd because of their level of flexibility. They can form star, mesh, and mixed topology networks, and can act as wireless serial bridges. But much of their popularity (at least of the Series 1, not so much the newer models which adhere more closely to the standard) is the ability to act as an airwire. The XBee can be configured to pass two analog signals in the form of 0-100% digital PWM, and then up to 6 more digital I\/Os, all without involving another microcontroller in the loop. To make my life even easier, Digi International provides X-CTU<\/a>,a useful GUI tool for configuring the radios to do your bidding.<\/p>\n

\"\"<\/a><\/p>\n

I yoinked two Xbee Adapter<\/a> boards from MITERS’ neighboring student activities so I could easily throw together a breadboard assembly.\u00a0 Each unit here is receiving 3.3 volts from the FSR board regulator. I set them up such that the transmitting unit receives the analog FSR voltage on AD0\/DIO0<\/strong> and an “enable” signal, on AD1\/DIO1<\/strong>.<\/p>\n

On the receiving side, the radio has PWM0\/RSSI<\/strong> hooked to the oscilloscope, along with its own AD1\/DIO1<\/strong>. Digital I\/Os are paired, but the analog ones have their own pins.<\/p>\n

Conveniently enough, RSSI was connected to a red LED on the boards.<\/p>\n

\"\"<\/a><\/p>\n

Configuring the radios to act as analog and digital airwires. There are relatively few settings to change, and most of them revolve around how to use the I\/O pins. I referenced Rob Faludi’s XBee I\/O page<\/a> (props for being the number 1 Google hit for the exact words “Xbee Direct I\/O”) and Digi’s own knowledge base page<\/a> on the matter. Needless to say, RTFM<\/a> came in handy also.<\/p>\n

The things I changed from the default firmware settings for the transmitting<\/strong> side, all values in hex:<\/p>\n