CANopen or SAE J1939? Choosing the right CAN protocol for joysticks

As construction machinery and other mobile equipment increasingly move towards electrohydraulic control, CAN communication is becoming an important part of joystick integration. But choosing a CAN joystick is not simply a matter of selecting a CAN output. OEMs also need to determine which protocol fits their machine architecture: CANopen or SAE J1939.

Both protocols are widely used in mobile machinery, but they serve different purposes and are not directly compatible. J1939 is strongly established in powertrain and vehicle networks, while CANopen is commonly used for working functions such as hydraulic valves, joysticks, I/O modules and sensors.

In this article, we look at the differences between CANopen and J1939, where each protocol is typically used and what OEM engineers should consider when specifying a joystick.

• Predefined messages Data is grouped in Parameter Groups, each identified by a Parameter Group Number (PGN). The individual signals are Suspect Parameter Numbers (SPNs), such as engine speed or coolant temperature. Because PGNs and SPNs are standardised, devices from different suppliers work together with little configuration. 
• Fixed bit rate 250 kbit/s is the classic J1939 bit rate; 500 kbit/s is defined in J1939-14. 
• Addressing Every node has a source address. Through address claiming, nodes can negotiate their address on the network. 
• Diagnostics Standardised diagnostic messages such as DM1 report active fault codes to displays and service tools. 
• Family ISOBUS (ISO 11783) in agriculture and NMEA 2000 in marine share the same higher-layer principles. 

J1939 is not limited to the powertrain. The standard also defines joystick messages, the Basic Joystick Message and the Extended Joystick Message, which carry axis positions and button states. Machines built around a J1939-based controller therefore often run their joysticks on J1939 as well. 

CANopen: the implement and working bus 

CANopen comes from industrial automation and is maintained by CAN in Automation (CiA). It is standardised as EN 50325-4. In mobile machinery it is widely used on the working side: hydraulic valves, joysticks, I/O modules and sensors. 

• Object dictionary Every device has a table of all its parameters and process data. The Electronic Data Sheet (EDS) describes this table in a file that configuration tools can read. 
• PDO and SDO Process Data Objects carry real-time data such as a joystick position. Service Data Objects give access to parameters, so settings such as filters, zero points and transmission intervals can be changed over the bus. 
• Network management NMT and heartbeat messages let the controller start, stop and monitor each node. 
• Flexible bit rate From 10 kbit/s to 1 Mbit/s, depending on cable length. 
• Device profiles Profiles standardise how a type of device presents its data. CiA 401 covers I/O devices, with a dedicated part 2 for joysticks, and CiA 408 covers proportional hydraulic valves. 
• Functional safety CANopen Safety (EN 50325-5) adds safety-related data objects that are sent twice, the second time bit-wise inverted, and is approved for use in systems up to SIL 3. 

The strength of CANopen is configurability. It suits machines where the OEM designs the working function itself, such as cranes, aerial work platforms, drilling rigs, material handling equipment and many European construction machines.

Two buses in one machine 

In practice the question is rarely "CANopen or J1939 for the whole machine". Many machines have two or more CAN networks: a J1939 bus for the powertrain and a CANopen bus for the working functions. The machine controller sits on both and acts as a gateway. It reads engine data from J1939, reads the joysticks from CANopen and commands the proportional valves for boom, arm, bucket and swing. 

Separating the buses also keeps bus load under control. A joystick that sends its position at a high rate does not compete with engine and aftertreatment messages for bandwidth. 

Which protocol for your joystick? 

The joystick follows the bus of the controller it talks to. A few practical rules: 

• Your controller reads operator inputs on a CANopen bus: choose CANopen. You gain configuration over the bus and, where needed, a route to CANopen Safety. 
• Your machine has a single J1939 network or a J1939-based controller: choose J1939. Standard joystick messages keep integration simple. 
• You build telehandlers, cranes, aerial work platforms or other lifting equipment: CANopen is the common choice, because load moment control and boom sensing are usually CANopen devices. 
• You use two joysticks, as on an excavator: make sure each can have its own node ID or source address, so both can share one bus. 
• You retrofit or build a simple machine without a CAN controller: an analog output, if required redundant, can be the most practical solution. 

CAN joysticks from Althen Controls 

Althen Controls supplies Hall effect joysticks for mobile machinery with either protocol. The C25, H4 and H6 series are available with CANopen output from 10 kbit/s to 1 Mbit/s or with SAE J1939 at 250 kbit/s. The J1939 versions can be ordered with different node addresses, so a left-hand and right-hand joystick can share one bus. For machines without CAN, the same joysticks are available with analog and redundant analog outputs. 

Building construction machinery? See how these joysticks are applied in excavators, wheel loaders and telehandlers on our Construction Machinery page.