# Best practices for “bus wiring”?

I have a device which implements a CAN bus and I need to connect 10 other devices to it. The descriptions I've seen of how these are wired show pictures like this:

The rig I'm making is a one-off (well, two-off actually, to support 20 devices total). I'm just trying to see if there is a some normal way one would make a pair of wires and then "tap it into them" at 10 different places. Obviously I can chop the wire and make a soldered connection at each point. I could also just run a separate pair of wires to each of the 10 points, all converging back to one point (but this makes a "star" instead of a "bus" which may screw things up).

Maybe this is a dumb question but is there some common tool that is used for this? To clip onto/into a wire in a case where you want to attach something to the line without having to cut it, solder the 3 contacts together, re-insulate it, etc.? (Wire nuts are an option too but also seem like it may be an inappropriate approach.)

EDIT: So far it looks like daisy-chaining them is the most practical approach. Whether it's with screwed-in contacts or other type of connector, just make sure I have two connectors on each device and then chain them together. That's where I'm at after looking at this off and on over a few days (and taking into account @Araho's advice).

• Generally, I've seen a set of paired screw terminals on the device, such that wires go all the way to the device, and then the next ones go on from there - but this does not apply equally to automotive solutions etc, so I won't post it as an answer. – Araho Apr 5 '17 at 22:21
• @Araho Thanks, yeah that's an option I hadn't yet considered. – bgp Apr 5 '17 at 22:22

There are indeed products that do this. Search for "solderless T tap connector".

The connector's metal contacts are designed to to cut into the insulator and grip the metal inside when crimping the connector onto the cable. I believe this is used in the automative industry though the last time I saw something like this was in industrial automation.

Before computer Ethernet LANs used RJ45 connectors and twisted pair cables they used BNC connectors and coaxial cables. There used to be BNC connectors that you can clip on to the cable that cut into the plastic and top the copper inside so you can quickly build an entire lab's network using a single long coax cable. But I can't find them on google anymore.

Another option, especially good for hobby projects, is to use a ribbon cable. Ribbon cable connectors are designed to bite directly into the cable without stripping or soldering. This has the side effect that you can tap into the ribbon cable at multiple places. Back in the day before SATA, IDE drives used this trick so you can install two hard disks onto a single ribbon cable. For serial communications, a 10-strand cable is just right.

• What you are referring to for coax were the "AUI vampire tap" interfaces. But they were used only for "thick" coax (the big yellow one used for 10base5 backbones, not the regular 10base2 coax that were brought to computer stations). – dim Jan 15 '18 at 12:07
• @dim: I distinctly remember the Engineering department at the University of Essex when I was an undergrad there wired their labs with 10base2 using such taps. So such things must exist because I physically saw them being used. – slebetman Jan 15 '18 at 14:26
• OK, I wasn't aware of this. But it is indeed possible. I think it was probably rather unusual on 10base2, though. – dim Jan 15 '18 at 14:35
• "solderless T tap connector" is exactly the thing I was looking for. Thanks. – bgp Jan 16 '18 at 9:03

The best way to daisy-chain "bus wiring," is to use T connectors for each device connected to the bus. The left side of the first T gets a terminating resistor as well as the right side of the last T. The same impedance cable is used from a right side to a left side of each T connector. This way, the chain can be very easily expanded or contracted, without affecting the impedance of the bus.

            ----      ----          ----
| 1 |     | 2 |         | n |
----      ----          -----
|         |             |
R--|---------|-------------|---R