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By: Vlad Cazan
I had two XBee modules that I really wanted to use with the mbed. These are the standard OEM RF Modules one with an antenna and one with a ANT chip. For one of the chips I will be using the Xbee Explorer USB from Sparkfun. http://www.sparkfun.com/commerce/product_info.php?products_id=8687
According to the datasheet (and Simon) of the Xbee modules, the following should be used as the pin layout. Main thing we are looking for first is power, ground, serial rx + tx, and a digital out for the reset.
1 VCC -------------- 3.3v 2 DOUT ------------- mbed serial rx (e.g. p10) 3 DIN -------------- mbed serial tx (e.g. p9) 4 not connected 5 RESET ------------ mbed digital out (e.g p11) 6-9 not connected 10 GND ------------- 0v/GND 11-20 not connected
| It is important to use the 3.3v pin (VOUT) and not the 5.0V (VU) or you might damage your Xbee module. Another important consideration is that the Xbee module has 2mm pin headers which will not fix on a standard breadboard. For this experiment I will be using male to female wiring. Sparkfun does have a breakout board which would work much better for a more permanent solution. http://www.sparkfun.com/commerce/product_info.php?products_id=8276 |  |
I have wired the pins accordingly using pin 9, 10 and 11 as the digital in, out and reset for the xbee. The second XBee is connected to a USB breakout board from sparkfun.
Using Simon's example from the forum I edited the code so that one xBee would "talk" and the other one would "listen". Since I still need power for the xbee unit the USB cable is still plugged into the computer but the communication is happening through the air. Using any terminal application if you type something from one mbed, the other will display. Nothing fancy, just a proof of concept. Will try creating something more interesting soon.
/**
* XBee Example Test
* A test application that demonstrates the ability
* of transmitting serial data via an XBee module with
* an mbed microprocesor.
* By: Vlad Cazan
* Date: Tuesday, September 29th 2009
*/
#include "mbed.h"
Serial xbee1(p9, p10); //Creates a variable for serial comunication through pin 9 and 10
DigitalOut rst1(p11); //Digital reset for the XBee, 200ns for reset
DigitalOut myled(LED3);//Create variable for Led 3 on the mbed
DigitalOut myled2(LED4);//Create variable for Led 4 on the mbed
Serial pc(USBTX, USBRX);//Opens up serial communication through the USB port via the computer
int main() {
rst1 = 0; //Set reset pin to 0
myled = 0;//Set LED3 to 0
myled2= 0;//Set LED4 to 0
wait_ms(1);//Wait at least one millisecond
rst1 = 1;//Set reset pin to 1
wait_ms(1);//Wait another millisecond
while (1) {//Neverending Loop
if (pc.readable()) {//Checking for serial comminication
myled = 0; //Turn Led 3 Off
xbee1.putc(pc.getc()); //XBee write whatever the PC is sending
myled = 1; //Turn Led 3 on for succcessfull communication
}
}
}
For the previous example I used the USB Explorer to mount the second XBee. For this example I have connected both XBee's to the mbed. Again the wiring is very easy, you only need 3 pins per each module and power and ground.
This code example takes a character from the terminal and adds 1 to its ascii value. Again not very useful, but proof it works. Imagin having two mbed's, they can now talk to each other wirelessly for up to 100 feet!
// basic xbee example
// - take chars from the terminal, push them out xbee1
// - listen on xbee2, and print value + 1 to terminal
#include "mbed.h"
Serial xbee1(p9, p10);
DigitalOut rst1(p11);
Serial xbee2(p13, p14);
DigitalOut rst2(p15);
Serial pc(USBTX, USBRX);
int main() {
// reset the xbees (at least 200ns)
rst1 = 0;
rst2 = 0;
wait_ms(1);
rst1 = 1;
rst2 = 1;
wait_ms(1);
while(1) {
if(pc.readable()) {
xbee1.putc(pc.getc());
}
if(xbee2.readable()) {
pc.putc(xbee2.getc() + 1);
}
}
}
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Do you have any thoughts on the best xbee modules to buy for development purposes? I am confused by the wide range of available options but my initial thinking was to buy two medium / high power with rpsma connections as this seemed to offer the best flexibility / price trade off ie: could be used to develop both short range and longer range projects. eg: http://www.sparkfun.com/commerce/product_info.php?products_id=8768.
Is there any reason to prefer Series 1 over series 2.5?
Thanks for the write-up.