[mizlplix]

Greetings to all:

I started this thread to gather information/experiences with CAN Bus communication. It seems to be a future technology that extends from vehicles to even large buildings.

I see at my workplace, the use of CAN Bus in our fire systems as well as our HVAC central controls. It is very flexible as well as precise in coordinating multiple units to allow them to operate as a whole. Even among units from different manufacturers.

I also gather that it has been building and growing for several years and finally emerging as THE common choice for inter-unit-communications.

My AC50/Curtis controller came with a nice wiring diagram. It lists a CAN Bus interface point. Has anyone used it to communicate with it?

The newer OBD2 vehicle scanners utilize CAN Bus in their software. Would one of these read a Curtis controller?

The interface plugs with attached wires exist for sale to facilitate this.

I was just wondering what the controller could do over this link?

Miz

[tomofreno]

Originally Posted by mizlplix

Greetings to all:

I started this thread to gather information/experiences with CAN Bus communication. It seems to be a future technology that extends from vehicles to even large buildings...
Miz

There's this: http://www.canbus.us/
Just started looking at it myself for similar reasons, so don't know much at this point.

[DaveAK]

While CANBus can be used to connect various systems it's a protocol for message transfer and the messages themselves are system specific. While the major auto manufacturers may have collaborated on a standard messaging systesm such as OBD2 there's no guarantee that any particular system will take with another, unless they speak the same language. It might well be that in the HVAC industry they have developed their own messaging standard to be delivered by CANBus. I'm not aware of any such efforts in the controller industry, i.e. I don't know if a Curtis Spyglass will work with a Sevcon controller, although they both use CANBus for connectivity. (At least I think the Spyglass is CANBus, but the principal of what I'm trying to convey is the same.)

So an OBD2 scanner that's CAN compliant might read the data from your Curtis, but it wouldn't be able to interpret it because the Curtis doesn't spit out OBD2 messages. The scanner might not even respond at all if it doesn't get OBD2 messages.

There are CAN interfaces that will read the CAN output from the Curtis and present you with the raw data, but then you need to have something that will interpret the messages. I've been working on cracking the Sevcon Powerpak controllers. You can read about my efforts here: http://www.davescomputerstuff.com/sevcon/sevcon.html.

[frodus]

note: spyglass is RS232, just a dumb terminal.

but I get what you're saying.

Curtis supports some J1939 messages via canbus and PID's. It's really not the adapter as much as the software that is running on your device (desktop, laptop, etc). The one's I've looked at seem to pass everything through to the canbus, it doesn't filter messages. That gets done in the software, which at this point, isn't written for the Curtis.

I'd love to work with people on this, I've got some ideas.

[DaveAK]

Originally Posted by frodus

note: spyglass is RS232, just a dumb terminal.

but I get what you're saying.

Curtis supports some J1939 messages via canbus and PID's. It's really not the adapter as much as the software that is running on your device (desktop, laptop, etc). The one's I've looked at seem to pass everything through to the canbus, it doesn't filter messages. That gets done in the software, which at this point, isn't written for the Curtis.

I'd love to work with people on this, I've got some ideas.

So does J1939 cover the actual messages themselves, or just the message format?

OK, found this on wikipedia "A PGN identifies a message's function and associated data. J1939 attempts to define standard PGNs to encompass a wide range of automotive, agricultural, marine and off-road vehicle purposes. A range of PGNs (00FF0016 through 00FFFF16, inclusive) is reserved for proprietary use."

Use of bold is mine to highlight what I said above. Also apparently J1939 did not original include CAN, but does now.

CANBus is like a telephone. You can use a phone to make a connection to someone in France, but unless you can speak French or they can speak English you're not going to be able to communicate.

[DaveAK]

One other caveat. All devices on the system have to be set to the same baud rate to be able to communicate. My Sevcon has a fixed baud rate of 100kbps. If Curtis supports J1939 it will most likely be communicating at either 250kbps or 500kbps and might be switchable between these two speeds.

As you can see, getting multiple devices to work together on one CAN Bus depends on many factors. Having said that it's pretty straightfoward to actually hook a PC to a CAN Bus device and get the data. It's also pretty easy to sniff the data going between two devices. What you do with the data, or what data you can inject in to the bus is where the fun starts.

[bjfreeman]

For the physical layer you can get a Canbus to USB adapter for you laptop.
I have a Java applet that show the raw messages, and then tries to Identify the type of messages and display them.
even J1939 is proprietary and can not be entirely decoded.
If someone wants to provide formats I wil be glad to add them to the app and provide it free off my website.