ECE497 Project: XBee

Team members: Stephen Shinn, Matt Moravec, Josh Dugan.

Executive Summary
The XBee project involves taking two series-one XBee modules (Include a link to these) and interfacing them with the various sensors that have been documented in our ECE497 group. Our goal was to create wiki sections which expand on the sensors to include sample wireless communication documentation and source code.

We have successfully connected to the XBee radios from the Bones and sent data using the  file system. We have also successfully done wireless implementations of the force sensitive resistor, the magnetometer, and the joystick alone a set of functions for expanding this to any sensor.

In conclusion, we're using XBee modules to communicate from one Bone to another. We have successfully communicated wirelessly with three sensors: the force sensitive resistor, magnetometer, and joystick. We hope that these instructions and code libraries are useful to hobbyists who wish to implement their own wireless solutions with the BeagleBone.

Hardware
The very first step is to solder your XBee module, see the instructions here. Once the module is assembled, you may wire-up the XBee module to the BeagleBone's serial ports. The table below describes how to hook up the module to UART2 on the Bone:

The image below shows the configuration:



Software
Our git repo for this project is available here: https://github.com/duganje/ECE497_XBEE.git. To begin, run beagle$ git clone https://github.com/duganje/ECE497_XBEE.git to clone the repository. This contains three folders with examples of XBee implementation for specific sensors and, which contains helper functions for using the XBee. You are now able to send data wirelessly using the  and   functions after running. Clone the repository on a separate BeagleBone and use the same functions to receive and reply data.

0.5" Force Sensitive Resistor
These instructions are for interfacing the 0.5" Force Sensitive Resistor with the XBee.

Required Items

 * 2 x BeagleBone
 * 2 x XBee Module
 * 2 x XBee Adaptor Kit
 * 1 x 0.5" Force Sensitive Resistor
 * 1 x 27kΩ resistor

Hardware
First we will connect the force-sensitive resistor to the Bone (P9 header). A 27kΩ resistor is used to connect the 3.3V source (pin 3) from the Bone to one pin of the force-sensitive resistor. Then, the other pin of the force-sensitive resistor is connected to ground (pin 1). An analog pin (AIN) on the Bone connects to the node containing both resistors, and values can be read off of that AIN. AIN5 (pin 36) is being used to read values on the Bone.

Next we will connect the XBee module to the Bone. The table below describes the necessary wiring.

With everything wired-up, your connections should match the image below. Click on the image to view the full resolution.



Software
We're going to start with these two pieces of code as a reference and combine them:


 * Code to interface with the force sensitive resistor
 * Code to interface with the XBee module

Running the code for the force sensitive resistor produces a value from 0 to 4096 depending on how much pressure is applied to the resistor. The harder the resistor is squeezed, the lower this value is. On line 46 of the force sensitive resistor code,  is constantly updated and stores this number.

The instructions now fork depending on whether you're setting up the sending XBee code or the receiving XBee code. When you're done you will have two C programs, one running on each Bone.

Sending
Start with the resistor code as a base and add the following include to the top of the file to add our XBee library (available here):


 * 1) include "XBee.h"

Next, add a call to  in   of the resistor code before the while loop begins.

In the  loop after the value of   is updated, add this line:

sendIntXbee(analogValue);

This will send the integer analog value to the receiving XBee. Now the number is constantly being sent in the while loop.

Receiving
Start with the XBee code as a base and create a  function. First in, add a call to   to setup the Bone to use the module.

Next, add a while loop to  which continuously receives the integer analog value from the other Bone using the   function. Once the integer value is received, you're free to use that information for whatever purpose you wish. The example code below should give you an idea of how this is done:

void main(int argc, char **argv, char **envp) { // Initialize XBee initializeXbee;

// Keep going while (1) { int analogValue = receiveIntXbee;

// Do anything based on analog value if (analogValue < 1000) ButtonPressedFunction; } }

Required Items

 * LED
 * 220Ω resistor

Instructions
Based on the instructions above, I've created a sample set of programs. Using two Bones, the send program runs on one and the receive program runs on another. The "send" Bone includes an XBee module and the force sensitive resistor, hooked-up as described here. The second Bone includes the XBee module hooked-up in the same way with the addition of an LED connected to pin 12 (GPIO1_28) of the Bone. Connect the ground pin of the LED to the Bone's ground (pin 1) using a 220Ω resistor.

Running both programs emulates the original function of the force resistor sample code, the only difference being that the data is now sent wirelessly from one Bone to another.


 * Send Program
 * Receive Program

To easily run the programs, follow these steps (you can skip the first step if you have already clone the repository): beagle$ git clone https://github.com/duganje/ECE497_XBEE.git beagle$ cd ECE497_XBEE beagle$ cd ForceResistor beagle$ make

This will create 2 executables: sendResistor and receiveResistor. Run the programs by running:

beagle$ ./sendResistor

on the Bone connected to the XBee and the force sensitive resistor and

beagle$ ./receiveResistor

on the Bone connected to the XBee and the LED.

You will then be able to squeeze the force sensitive resistor and see the LED light up on the other BeagleBone. We've created a YouTube demo of this program in action.

Wireless 2-Axis Thumb Joystick
These instructions are for interfacing the 2-Axis Thumb Joystick with the XBee. This application could be useful in a wireless controller setting.

Required Items

 * 2 X BeagleBone
 * 2 X XBee Module
 * 2 X XBee Adaptor Kit
 * 1 X 2-Axis Thumb Joystick

BeagleBone Wiring Instructions
On your first BeagleBone, wire pins 36 and 38 to your two analog inputs. Wire the Beagle's 1.8V VCC output, pin 32, to the VCC input of the Joystick. Finally, wire the select GPIO signal to the GPIO_7 pin or pin 42.

Wire the XBee as shown in the table below:

The pinout and visual implementation are shown below.



On the second BeagleBone, wire the XBee exactly as the first XBee (as described in the table above).

Don't hook up any other hardware to the second XBee as it will be acting as an information hub.

Usage Instructions
On both BeagleBones, clone this repository: https://github.com/duganje/ECE497_XBEE.git Use the following to run the joystick code (you can skip the first step if you have already cloned the repository):

beagle$ git clone https://github.com/duganje/ECE497_XBEE.git beagle$ cd ECE497_XBEE beagle$ cd 2AxisJoystick beagle$ make

This will create 2 executables: joystickSend and joystickReceive. Run the code by doing:

beagle$ ./joystickSend

on the Bone connected to the XBee and the joystick and:

beagle$ ./joystickReceive

on the Bone connected to just the XBee.

Magnetometer
These instructions are for interfacing the HMC5883L Magnetometer with the XBee.

Required Items

 * 2 x BeagleBone
 * 2 x XBee Module
 * 2 x XBee Adaptor Kit
 * 1 x Magnetometer Breakout Board
 * 2 x 4.7kΩ resistor

Hardware
The XBee radios should be connected to both Beagles as shown in the table below.

The Magnetometer should be connected to one BeagleBone as described in the hardware section of the Magnetometer page. Ground and Vcc on the Magnetometer should be connected to pins 1 and 3 respectively on header P9 of the bone. SCL and SDA on the Magnetometer should be connected to pins 19 and 20 on P9 to use I2C bus 3. Two 4.7kΩ resistors should also be connected between SCL and Vcc and between SDA and Vcc. Below is a picture of the Beagle connected to the Magnetometer and the XBee.



Software
The goal is to have the two BeagleBones attached to XBee radios with the one connected to the Magnetometer taking data and transmitting this data to the other Bone which will print the measured data.

I started with the code to collect data from the Magnetometer and the code to send data using the XBee radios. Here are the links to these two programs:
 * Code to gather magnetometer data
 * Code to interface with the XBee module

The code for the magnetometer uses I2C to read the values for the X, Y and Z-Axes and print these values to the terminal. The XBee code contains helper functions to transmit data wirelessly. I have written two programs: one to collect and transmit the magnetometer data and the other to receive and display this data.

Sending

 * Tranmitting Magnetometer Data Code

The code uses I2C code from EBC Exercise 12 I2C and helper functions from XBee.c.

The program uses:

i2cget(i2cbus, address, daddress);

to get the data from the magnetometer and

sendShortXbee(val);

to send these values to the receiving XBee.

Receiving

 * Receiving Magnetometer Data Code

The receiving code uses:

receiveShortXbee;

to read the values for each axis.

Because we do not have a way to synchronize the two XBees, the receiving program must be started first to ensure the data is receive in the correct order.

In the Highlights section, there is a video demo of the complete program.

Running the Code
Use the following to run the magnetometer code (you can skip the first step if you have already clone the repository):

beagle$ git clone https://github.com/duganje/ECE497_XBEE.git beagle$ cd ECE497_XBEE beagle$ cd Magnetometer beagle$ make

This will create 2 executables: receiveMag and sendMag. Run the code by doing:

beagle$ ./sendMag

on the Bone connected to the XBee and the magnetometer and:

beagle$ ./receiveMag

on the Bone connected to just the XBee.

General Usage
These instructions are a general how-to for using the XBee with any sensor.

After cloning our repository to your favorite location, include the necessary header file,. In your  file or your program, first run: initializeXbee; which sets the pins we will need to communicate with the XBee using UART 2. Then in your  file, call: sendIntXbee(yourInt); with   being any integer data you would like to transmit. On your 2nd BeagleBone, call: receiveIntXbee; which will return the integer which was sent through  on the 1st board.

The send and receive functions can be easily modified to send any data type, as shown in  with the following functions:

sendShortXbee(short yourShort); receiveShortXbee;

Highlights
Our project is able to send and receive wireless data for a whole range of possible implementations. We've created YouTube demos for the three sensor implementations we've described so far:

Theory of Operation
The main theory of operation is based on Linux's use of files. UART files on the Bone represent serial connections. With an XBee connected to the Bone's UART 2 as shown above, sent and received messages are written to  (the O is an uppercase O, not a zero). The BeagleBone's UARTs are accessed through, where   is the UART number. Our code uses this and reads the file to receive a message and writes to the file to send a message. Any XBee's on the same network wil receive the message and we can do anything we want with it.

Milestones

 * Monday, 10/29 - XBee hardware received. (done)
 * Thursday, 11/1 - XBee Bones are connected and commands can be sent. (done)
 * Monday, 11/5 - Initial sensor implementation. (done)
 * Thursday, 11/8 - Package language implemented between Bones. (done)
 * Sunday, 11/11 - YouTube demo uploaded. (done)
 * Monday, 11/12 - All documentation complete. (done)
 * Tuesday, 11/13 - Everything complete & all code makes. (done)

Completed Work

 * Soldering XBee's - Matt Moravec
 * Initial communication methods - Stephen Shinn
 * Expanded communication methods - Josh Dugan
 * Initialization method - Josh Dugan
 * Force Sensitive Resistor implementation and demo - Stephen Shinn
 * Magnetometer implementation and demo - Josh Dugan
 * 2-Axis Thumb Joystick implementation and demo - Matt Moravec

Future Work
The following are some additional things that could be done with this project:


 * Create and document interfaces for more sensors
 * Back-and-forth 2-sensor communication
 * Create a practical application such as a wireless doorbell

Conclusions
In conclusion, we created an XBee wireless communication library for BeagleBone and adapted three sensors to use it. We've also documented general usage instructions for adapting XBee to use any type of sensor. We have not found a comprehensive source for how to use XBee modules with the BeagleBone, so our code and instructions are online with the intention that others use them as a reference.

We were unable to get a working program with 2-way communication with 2 XBees each sending and receiving data because of synchronization problems. Addressing this would require the development of a communication protocol to prevent deadlocks and to ensure the receiving program knows what the data is when it receives it. This would be a logical next step in terms of future work for this project.

Using the wireless modules is interesting, and there is a number of things you can do with them. We've listed a few ideas above which could be done in the future. One interesting idea would be to create a practical XBee application that someone could actually use in their home or work life. With a few XBees around the house, one could have a small network for sending data and using a sensor to control Christmas lights or something.