For what it’s worth, our RJ11s have have four pins installed and six channels, just like a normal teleco connector.
Hugh,
How did you get a good crimp on the cable with the round(ish) Ethernet cable? It would seem like with most of the wires removes the top part of the connector might not grab the outside shell of the cable very well. Did they tend to come off, did you do something special, or did it just happen to work?
Dale
Al, are you sure you’re not thinking of the handset plug (sometimes incorrectly called an RJ9)? An RJ11/12/14* jack has all of the necessary “slots” for the spring wire contacts on the Jaguar side and should not allow those spring contacts to move and touch each other. The only difference between the RJ11, RJ12/RJ25, and RJ14 is that the RJ11 has only 2 positions populated with contacts, the 14 has 4 loaded, and the 12/25 has all 6 loaded (but all 6 positions still exist in each case).
If anything, I would expect that an RJ14 would allow the outside spring contacts to sit even deeper in the plastic “slot” than an RJ12 because without a contact in the outside positions of the plug, the “slot” is actually deeper than a populated one.
Dave,
There is a lot of confusion out there on these jacks including the Jaguar docs. The cheaper RJ11 jacks do not always have the depressions you speak of where the two outside contacts of a six position plug would normally be located. However, I have seen teams using the handset plug (which is narrower than a standard RJ11) this year. Specifying the six position connector prevents any ambiguity. Although one pin of the connector is labeled +5volts, that is not connected to any power supply internal to the Jaguar. If other sensors are used to that provide power on that pin, misalignment could cause some other serious issues. Also a crimper that is designed for four position plugs will not push in on the outer contacts of a six position plugs when assembling these plugs.
Dale,
It clamps down about like on a RJ45 network connector. We just try to push the outer insulation into the connector before making the crimp. Even if it comes out the wires are still securely held by the crimp pins deeper in the connectors.
Hugh
That would kind of defeat the advantages of CAN networking though (the added complexity of the “router”)
But there is no reason CAN can’t be used in a star topology. We use a star topology in the cars where I work, on both the 125 kb/s and 500 kb/s networks. The key is proper terminations.
Terminating resistors are intended to prevent the signal reflections that occur at the end of an open-circuited wire. What happens is the signal hits the open wire end (at the speed of light) and bounces back into the network (at full amplitude). Do this just wrong and your data bits turn into garbage.
A good tool to see if your star network is well-terminated is an oscilloscope. Compare a known-good signal to your network.
Regarding noise: A CAN-Bus is inherently resistant to noise, since it uses differential signaling. It is the difference between CAN-H and CAN-L that determines logic 0 or 1. In theory, both wires of the network will be affected equally by some induced noise, while the difference between the wires remains constant. In practice, the noise induced into each wire is “same” enough to work against noise very well.