Description

Not all sensor network applications can deal with the wiring involved with a wireline CAN solution. Sometimes there is a just a gap that cannot easily be crossed with a wire. Other times it is just not practical, for example because the system is a temporary setup, which does not warrant clean installation of the wiring involved.

CAN-bus is really just intended a wire-based technology and must of it's features depend on the physical medium. However, if we don't bother too much about priorities and bus error features, then there is no reason not to route CAN-bus telegrams over a wireless medium. This is also acknowledged by CAN in Automation, the group behind CANopen, with their publication CiA 315 "Generic frame for wireless tunneling of CAN messages and for transfer of diagnostic data".

WiCAN is a wireless solution for CAN-bus connectivity. Concentrators connect to various CAN-bus devices or segments and pair them wirelessly. Or they receive data from CANopen devices with build-in WiCAN connectivity.

Functionality

• Wireless networking for CAN-bus data
• Bridges operate as CANopen^® device with device monitoring & configuration and SYNC regeneration
• Transparent for J1939 or other 29-bit CAN applications
• Supports more than 100 nodes in the wireless domain
• Configuration via CANopen or via PC application on micro-USB port
• Possibility for branding or custom firmware with specific behaviour

Specifications

• IEEE 802.15.4 protocol using XBee technology
• Globally approved 2.4GHz ISM band
• Maximum wireless bandwidth ~100kbps
• Distance 60m indoors, up to 1200m outdoors
• Large FIFO buffers allow for buffering of bursts on either side
• Separate priority FIFO helps in preserving timing of messages with ID ≤ 0x100
• CANopen SYNC message PLL on receiving devices to reduce radio latency jitter effects
• Supports LSS node ID assignment and Fastscan (CiA 305)
• Supports firmware update via wired or wireless CAN interface, including firmware of the XBee radio module
• Supports power management & monitoring features (CiA 302-9 + custom)

Devices

Bridges or concentrators are needed to connect the WiCAN wireless sensors to the physical CANopen network. The concentrators also enable CAN-bus bridging over the air.

Bridge/concentrator

Wireless CAN-bus Bridge & concentrator.

Ambient sensor

Wireless CANopen Temperature, humidity & VOC sensor.

Digital Multimeter

Wireless Digital Multimeter (DMM) using CANopen protocol.

Wireless performance & limitations

Connecting CANopen devices over a wireless link strips some of the reliablity and ruggedness features of the CAN bus protocol. Additionally, there are bandwidth limitations that are less easiliy defined than with a wireline approach. Use of more than 2 bridge devices in a network results in multicast transmissions, which decreases effective bandwidth proportionally to the number of bridges. When the wireline feed bitrate and message rate exceeds the available RF bandwidth, increased message latency may occur and ultimately message loss.