Near Intersection of I-35 & I-90 Southern Mn. | Portfarm. This might work fine but I would recommend using doing it the suggested method. The terminator idea is to prevent reflections and interference. I agree that it seems like a bunch of extra parts at the very end but I think you should get them and install the terminator at the last most distant junction. You really don't want to have some issues anytime due to communication but especially with a newly installed system as there may be other areas of confusion.
I worked with these as a Tech and also as an end user of my own equipment. I happened to catch a YouTube video last week that added some information. I am far from an expert on the topic.
The Ag Leader CAN system and others use 4 wires. The red is power, the black is ground, the green and yellow carry the pulses of information so the various modules can communicate with each other. These colors are somewhat of an industry standard.
Part of the reason for using two wires to carry the information rather than just one is for interference issues. If a single wire was used, electrical noise (from an Alternator, radio etc.) could introduce a "spike" on the information line causing misinformation to be delivered to the other modules. Instead these pulses of information are delivered using both the green and yellow wires simultaneously. One wire goes to a positive voltage while at the same time the other wire goes to a negative voltage. A valid pulse is then the "difference" between the two. If your alternator created a spike which reached the wires, both the wires would be subjected to the spike but the difference would still be valid. This means they can use a green and yellow wire twisted together about one turn per inch rather than needing the more expensive and difficult to work with CoAx cable.
Ag Leader systems often involve several CAN cables that may connect several modules to the display cable. CAN extensions are available in various lengths. These extensions have the same connector on both ends. To connect them to each other either to gain length, allow a split or connect to a stub cable to a module requires the use of a "Y" connector. These "Y" connectors can be connected in various ways and even though the branches are different colors they are all equivalent. There is no magic in the "Y" connectors. They are equivalent a Tee in plumbing terms.
Ag Leader systems use "plugs" in various locations. One type is called a terminator. It plugs into one of the branches of the "Y" connectors. It contains a 120 ohm resistor. If you look at a terminator you will see that only two sockets are present. These mate with the green and yellow wires. If you should dig out the rubbery material, you would see a 120 ohm resistor connected between the two sockets.
The other type of plug is just a dust plug. It plugs into one of the branches of a "Y" connector also. It has no electronic purpose. Its only purpose is to act as a dust plug to prevent damage to that branch.
Each system should have two terminators involved. Their purpose is to prevent/eliminate "electronic reflections" and "interference". Generally speaking each system should have a terminator at each "end" of the CAN chain of connections. Early Ag Leader display cables had a branch where a terminator could be installed in the display cable. Newer display cables have this built in.
This means that ideally there should be a loose terminator plug installed at the very last "Y" before the most distant module. This is the one that you are considering leaving out. I think you should have one there.
On simple systems with only one module this is very straight forward. Insert a "Y" connector between the CAN cable and the stub cable leading to the module and insert a terminator on the unused branch. The system would then have a terminator on the module end and also a terminator on the the display end that is built into the display cable.
Many systems get more complicated with several modules. If you think of them as a long chain of modules, then you would again insert the terminator in the most distant "Y at the junction to the that module. You would use "Y"s along with way to branch off to a module and an extension to the next "Y" module another extension and so on. Again put a terminator at the most distant "Y".
Suppose your extension is not long enough and you need to put two together to gain the length needed. This is done with another "Y". This is where the dust plug is used. You do not want to use a terminator on that "Y" so use a dust plug which protects the unused branch. You have in effect made two short extensions into a longer one.
I noticed on my combine CAN cable layout that excess cabling seemed to be used. Since 3 modules are used, it would seem that they could have just split the CAN connections right out of the cab with two "Y"s to lead to the 3 modules. Instead they ran the CAN cables in a long loop from one to the next with the terminator at the last module.
I had a personal installation where it was desirable to split the CAN bus and run one branch out the side of the tractor and another out the back. There was a single module out the side but a pair of modules out the back. The terminator question then was should I put a terminator on the "end" of each branch or should I put a single terminator at the end of the longer branch going out the back and use a dust plug for the branch going out the side.
I opted to just use a dust plug on the short branch and the terminator on the long branch and it worked fine. I believe putting a terminator on the short branch also would have been undesirable but may have worked. The idea of the two terminators of 120 ohms each is that they are then connected in parallel across the green and yellow wires. Two 120 ohm resistors wired in parallel result in a resistance of 60 ohms. Had I used an "extra" terminator, the system would then have had 3 - 120 ohm resistors in parallel or 40 ohms equivalent. This might have caused problems.
So wrapping it up, two terminators are desirable in any system, one at the display (built into present display cables) and one at the most distant end of the CAN chain. Could you get by with only 1? Could you have problems by using too many terminators? I'm not certain but I suggest "playing the game".
Edited by tedbear 5/27/2023 07:16
|
Agleader CAN terminator required?
