(French version)

• Author: Jérôme Abel (Reso-nance)
• Date: 09/2014
• License: GNU/FDL3
• Files: codes.zip
• Thanks to: Martin Peach, Hans-Christop Steiner, Vincent Pillet

Xbee modules are used to transmit wireless data (radio waves). If you don't know anything about that and you are brave, you should follow a tutorial or mine but it is in French : Xbee & Arduino.

On the last tutorial we've seen how to make a “point-to-point” network, instead of wires. One Xbee talk to another one. Now, I focus on the star network topology wich allows two setups : one emitter (coordinator) send data to few receivers (End Devices) ; and in return, few emitters send data to one receiver. This article describe how to do this with XBee Series 1, Pure Data and Arduino. Some of my art projects (Patatas de goma and Chimères Orchestra) will use this technique.

• Basics of Pure Data, Arduino
• Basics of Serial Communication (in French)
• Basics of Xbee & Arduino (in French)

Used for tests:

• 3 XBee series 1 + 3 mini-boards
• 3 Arduinos
• 2 Serial converter ou XBee explorers
• 3 Breadboards
• 4 Leds
• 2 Battery couplers 1,5V AAA + 4 batteries
• Jumper wires

To install:

• Pure Data Extended, which contains [mrpeach/packxbee] and [mrpeach/unpackxbee]
• Arduino
• Processing
• xbeeterminal.zip (made in processing), to setup XBee
• Additional libraries (in “codes.zip”): xbee-api, xbee-arduino et SerialCommand

• XBee Datasheet : xbee_product_manual.pdf
• XBee Arduino : XBeeAPIsTutorial, XBee Arduino Developers Guide etXBee series 2 quick reference guide
• XBee Pure Data : xbee_io_reader.pat et lists.puredata.info

Some precautions et common mistakes :

If you open twice the Arduino software, you can upload codes into two different Arduinos. It avoids change the board name each time.

The first example is to control directly digital and pwm outputs of XBees with Pure Data, without Arduino. We connect LEDs on the D0 (digital) and PW1 (PWM) pins of the XBee.

Schematic : Pd/AT/SERIAL/XBEE1 —> XBEE2/LEDS, XBEE3/LEDS, …
Code : to-xbee-star.pd

Open the xBeeSerialTerminal with Processing and setup XBees :

• XBEE#1 Coordinator: ATRE, ATID1111, ATAP2, ATCE1, ATWR
• XBEE#2 End Device : ATRE, ATID1111, ATMY2, ATWR
• XBEE#3 End Device : ATRE, ATID1111, ATMY3, ATWR

The main difference between last setups is that we do not write the destination address. The address is part if the message sended by Pure Data to the coordinator. It is because we use the API mode (ATAP2). See appendices at the bottom to know more.

Notes :

Send commands with Pure Data :

Remote AT commands (RAT)

We can understand what is in Xbee packets with serial monitoring.

Schematic : Pd/SERIAL/XBEE1 —> XBEE2/RX/ARDUINO
Fichiers : to-xbee-serial.pd, from_serial.ino, from_xbee_serial.ino (get packet), from_xbee_serial_2.ino (get one data)

Note : when I use simply the serial converter without Arduino, I catch nothing… I don't understand.

• XBEE#1 Coordinator: ATRE, ATID1111, ATDL2, ATWR
• XBEE#2 End Device : ATRE, ATID1111, ATMY2, ATWR

One Arduino send data to two other to understand how to send and receive Xbee packets. We wire a LED to pin 9 of each End Devices Arduinos to see what it is happen.

Schematic : ARDUINO/TX/XBEE1 —> XBEE2/RX/ARDUINO/LED et XBEE3/RX/ARDUINO/LED
Codes : to_xbee_api.ino, from_xbee_api.ino

• XBEE#1 Coordinator: ATRE, ATID1111, ATAP2, ATCE1, ATWR
• XBEE#2 End Device : ATRE, ATID1111, ATAP2, ATMY2, ATWR
• XBEE#3 End Device : ATRE, ATID1111, ATAP2, ATMY3, ATWR

To use Pure Data and send Xbee packet, I had no success in using only a serial converter. I needed use an Arduino to make real XBee packets for the receivers. I use the SerialCommand library in Arduino to parse 6 data from Pure Data (a list). These data are formatted by Arduino and the XBee library. Receivers get only the good data from the packet. The LED is connected to the pin 9 to see what it's going on.

Schematic : Pd/CMD/ARDUINO/XBEE1 —> XBEE2/RX/ARDUINO/LED et XBEE3/RX/ARDUINO/LED
Codes : to-xbee-cmd.pd, to_xbee_api_cmd.ino, from_xbee_cmd.ino

• XBEE#1 Coordinator: ATRE, ATID1111, ATAP2, ATCE1, ATBD6, ATWR
• XBEE#2 End Device : ATRE, ATID1111, ATAP2, ATMY2, ATBD6, ATWR
• XBEE#3 End Device : ATRE, ATID1111, ATAP2, ATMY3, ATBD6, ATWR

The coordinator get data directly from sensors connected to XBee senders whithout Arduinos, with Pure Data or Processing. Very useful to get data from a network of sensors.

Schematic : SENSOR/XBEE2 et SENSOR/XBEE3 (only) —> SERIAL/XBEE1
Codes : from-xbee-star-1.pd, from-xbee-star-2.pd

• XBEE#1 Coordinator: ATRE, ATID1111, ATAP2, ATMY1, ATWR
• XBEE#2 End Device : ATRE, ATID1111, ATAP2, ATMY2222, ATDL1, ATWR
• XBEE#3 End Device : ATRE, ATID1111, ATAP2, ATMY3333, ATDL1, ATWR

Les adresses des destinataires doivent être celles du coordinateur.

Without [mrpeach/unpackxbee]

With [mrpeach/unpackxbee]

processing-codes

In AT Command mode (Transparent Mode) , everything got in RX of XBee will be sent out via antenna , the incoming data from antenna will go to TX. But in API Mode , it won't send out anything until it received the correct form of commands from serial interface. (xbee introduction)

Data Structure in API Mode:
7E 00 0A 01 01 50 01 00 48 65 6C 6C 6F B8

Series 1 radios support both AT and API modes with a single firmware version, allowing you switch between the modes with X-CTU. However, Series 2 requires a specific firmware for API mode. As of now there are two firmware versions for Series 2 API mode: ZNet and ZB Pro. ZNet is recommended as it is the easiest to work with.

What is API (Application Programming Interface) Mode and how does it work? (digi.com)
API (Application Programming Interface) mode is a frame-based method for sending and receiving data to and from a radio's serial UART. The API is an alternative to the default transparent mode. The API allows the programmer the ability to:

• Change parameters without entering command mode (XBee only)
• View RSSI and source address on a packet by packet basis
• Receive packet delivery confirmation on every transmitted packet

XBee product manual :
The API operation option facilitates many operations such as the examples cited below:

• Transmitting data to multiple destinations without entering Command Mode
• Receive success/failure status of each transmitted RF packet
• Identify the source address of each received packet

To send data to few modules, another way would be to send messages to everyone (broadcast). Then the receivers parse data to get only what they want. I think the API mode seems to be “The” way to achieve that. In real, the message is physically send throuh air (radio waves) like a broadcast. XBee modules seems manage data to know which data are the good ones, etc.

Series 2 (forum.sparkfun.com) :
Transmitting data using broadcast addressing with XBee ZB modules will generally give you much, much less performance than transmitting an individual unicast to each node you want to talk to. This is because broadcasting works very differently on the XBee ZB modules than with the XBee 802.15.4 modules.

Series 1 (forum.sparkfun.com, electronics.stackexchange.com) :
If you don't want to use API, and strictly want to use AT mode, then I suggest you simply put a destination prefix string at the beginning of each of your messages, and then broadcast all messages to all end-nodes. On the receiving end-nodes, write some code to check whether the destination prefix string of a received message matches that particular end-node's address/name (which you can assign randomly yourself in code). I don't think it's a good idea to change ATDL dynamically for each message. Not only might it affect the timing and require re-pairing but also remember that ATDL is written to the Xbee's EEPROM – which only allows a finite number of rewrites.