A small demo app for the python-xbee library

We used this script as a starting point for an XBee/ZigBee project when we were trying to figure out how to get an Arduino and a RaspberryPi talking to each other over ZigBee (Xbee chips).

What does it do?

The script implements basic ping-pong messaging. The hub (RaspberryPi) waits for a message, prints the message to stdout, and replies with a "PONG" message.

The edge node sends an initial "PING" message after which it prints out any received messages and replies to the sender with another "PING" message.

We ran the script in hub mode on a Raspberry Pi and in edge node mode on a laptop (the XBee chip was connected to the laptop over a USB cable and one of these.

How do I run the scripts?

The hub:

export XBEE_PORT=/dev/ttyAMA0
export IS_HUB=True
python xbee-demo.py

The edge node (laptop):

export XBEE_PORT=/dev/tty.usbserial-A1011HQ7
python xbee-demo.py

The hub out put should look something like this:

$ python xbee-demo/xbee-demo.py
run...

current status:

AT - ID = 00000000deadbeef
AT - SH = 0013a200
AT - SL = 40acc066
AT - MY = 0000

hub node - waiting for data
RX - {'source_addr_long': '\x00\x13\xa2\x00@\xb4\x175', 'rf_data': '\x03\xae', 'source_addr': 'k\x08', 'id': 'rx', 'options': '\x01'}
tx_status - {'retries': '\x00', 'frame_id': '\x01', 'deliver_status': '\x00', 'dest_addr': 'k\x08', 'discover_status': '\x00', 'id': 'tx_status'}
RX - {'source_addr_long': '\x00\x13\xa2\x00@\xb4\x175', 'rf_data': '\x03\x96', 'source_addr': 'k\x08', 'id': 'rx', 'options': '\x01'}
...

The edge node output should look something like this:

% python xbee-demo/xbee-demo.py
run...

current status:

AT - ID = 00000000deadbeef
AT - SH = 0013a200
AT - SL = 40b41735
AT - MY = 6b08

edge node - send frame to
tx_status - {'retries': '\x00', 'frame_id': '\x01', 'deliver_status': '\x00', 'dest_addr': '\x00\x00', 'discover_status': '\x00', 'id': 'tx_status'}
RX - {'source_addr_long': '\x00\x13\xa2\x00@\xac\xc0f', 'rf_data': 'PONG', 'source_addr': '\x00\x00', 'id': 'rx', 'options': '\x01'}
...

As you can see, the edge node initiates the messaging by sending the first message (the edge node log starts with a tx_status).

How to configure the XBee chips?

I won't go into a lot of detail on how to configure the chips. Basically we used X-CTU on a Mac to flash the Coordinator API firmware on the hub node chip and the End Device API firmware on the edge node chip.

We then set the PAN ID to 0xDEADBEEF in our case (come up with your own PAN ID for you project ;-).

Addressing

One of the key discoveries for us was to work out how to address the hub node. In our use case the edge nodes will initiate comms with a request to the hub and the hub will reply to the edge nodes.

The python-xbee ZigBee.tx calls require both a long destination address (dest_long_addr) and a short destination address (dest_addr). To address the hub (ie a Coordinator node) we can use a long destination address of 0x0000000000000000 and a destination address of 0xFFFE (unknown / breadcast address). These addresses allowed us to send a message successfully from the edge node to the hub.

The hub can pick up the sender addresses from the packet and use those when replying to the edge node.

Requirements

This demo works with the python-xbee library.

XBee vs. ZigBee

The python-xbee library provides both an XBee class and a ZigBee class. Turns out that the ZigBee class implements the ZigBee protocol, whereas the XBee class implements the lower level IEEE 802.15.4 protocol.

Our example script uses ZigBee rather than XBee.