How can I send strings of data to an XBee with a python library?

Question

Which library should I be using, and how?

Python XBee seems to be only able to send commands in API mode, and I can't find an example of anyone using it to send a string. Maybe I'm misunderstanding what API mode is, but I can't find a payload in the documentation...

Are Digi's Python Socket extensions baked into Python? I can't seem to get any of the constants they claim to have defined in my Python (2.7.3rc2), nor can I find a mention of how to get these extensions on their site. It seems like that could be a way to pass around strings, but how do I use it?

Ruffina

Answer 1

If the Xbee is connected to the computer as a serial device you can just use a serial library such as pySerial. Here are some code snippets from a project I just finished.

# Connect to Xbee
self.ser = serial.Serial(port, baud, timeout=timeout)

# Send data (a string)
self.ser.write(packet)

# Read data
self.data += self.ser.read()

We were using the Xbees in transparent mode - each byte you write on one end is visible on the other end with a read. There was no need for a special Xbee library.

Hadlock

So the XBee on the serial port will repeat that string onto the XBee network, and also write all data it receives from remote XBees to serial? I assume both XBees need to be in transparent mode? – Ruffina

I have only ever worked with two Xbees communicating directly, never with a larger network. If both are in transparent mode than any byte you write on one end will appear on the other end, just like normal serial. – Hadlock

Answer 2

I would also recommend using pySerial if you have a very simple setup and only two XBees, but if you have anything more complicated then you are better off with a library.

The python-xbee library is quite simple to use but does lack any sort of comprehensive documentation. To send and receive simple message using it:

from xbee import XBee
from serial import Serial

PORT = '/dev/ttyUSB0'
BAUD = 9600

ser = Serial(PORT, BAUD)

xbee = XBee(ser)
# Send the string 'Hello World' to the module with MY set to 1
xbee.tx(dest_addr='\x00\x01', data='Hello World')

# Wait for and get the response
print(xbee.wait_read_frame())

ser.close()

You can send AT commands by doing:

xbee.at(frame_id='A', command='MY')
reply = xbee.wait_read_frame()
print(reply)

# Getting the integer value out of reply
import struct    
print(struct.unpack('>h', reply['parameter'])[0])

You can set the frame_id to any string, and it is used to identify the correct reply.

Detonate

I recently took over the management of python-xbee (the one you pip install) as it hadn't been updated for years. I'm happy to accept pull requests that improve documentation! github.com/nioinnovation/python-xbee/blob/master/docs/source/… – Wanton

Answer 3

The first question is "Are you sure your devices are in API mode?". You are seeing this error because the receiving end is seeing a frame of type 'tx' (type 0x01) coming in. Although this is the frame you have requested to be sent I believe you would expect it to be received as type 'rx' (type 0x81) by the receiving end.

If you look at the code in /xbee/ieee.py you will see two lists: * api_commands = Outgoing: You would never expect one of these frame types incoming. * api_responses = Incoming: You should only see these frame types incoming.

If the library detects one of the api_commands incoming it will throw the error you see: "Incoming frame with id 1 looks like a command frame of type 'tx' (these should not be received). Are you sure your devices are in API mode?"

I am not 100% sure of your situation but it looks like your outgoing 'tx' frame is not being translated to an incoming 'rx' frame at the other end - possibly API mode not enabled on all XBees?

Also see https://github.com/nioinnovation/python-xbee/issues/44

Loeb

Answer 4

ser = serial.Serial(SERIAL_PORT, 9600)
bee = ZigBee(ser) # <--

Try to use ZigBee instead of XBee, if it fails.

Blanco