Repairing cut wires on 1200

[ahutcheon]

CANBUS is a two-wire (normally) multiplex network with a (rather elegant) priority-base arbitration scheme to ensure that only one message appears on the bus at any one time. The driver circuitry is pretty robust (I used to write software that runs the networks in, amongst other things, Volvos (cars and buses) and Fords). As a software guy hooking up prototype hardware I probably committed most of the short to earth/12v crimes that the designers protect against. I even ran CANBUS signalling between devices in different labs using the building's structured cat6 wiring, so the physical wiring specs have a bit of leeway...

CANBUS is a bit like baby ethernet, and there is no way you could fake a signal packet by shorting wires (even with a very shaky hand you won't manage a sequence of 129 bits + bit stuffing and the error correcting code). I'd bet you could cut an active CANBUS, solder it back together, and the message interrupted by the cut would send as the wires rejoined. You won't turn anything on or off by accident.

Ah, nostalgia. Apologies that the technical content probably resembles gibberish...

 

[MattW]

Wow.
This is the longest thread about sticking a couple of wires together that I've ever seen

(although the technical stuff about controller area networks is very interesting)

 

[Doofus]

...there is no way you could fake a signal packet by shorting wires (even with a very shaky hand you won't manage a sequence of 129 bits + bit stuffing and the error correcting code). I'd bet you could cut an active CANBUS, solder it back together, and the message interrupted by the cut would send as the wires rejoined. You won't turn anything on or off by accident...

you will if you short two wites together that run to switch - you might not generate the bit stream, but the controller will generate it for you when your short pulls up / down the corresponding input to the controller.

 

[darkhorse]

Dave

If you haven't soldered for a while get some practice in first. Pull a few wires out of your PC and see if you can rejoin those.



Get some heat-shrink tubing. The higher the ratio, the better.

Get some soldering flux (in a tin) and use fluxless solder. Dab the bare wires in the flux and then drag through a dob of molen solder on the end of your iron without trying to join the wire at this stage. When you have all the wire ends 'tinned', then start joining them (you won't need any more flux and only the smallest amount of solder on your iron (which acts as a heat-transfer medium only).

If you have three hands, so much the better.

Job done



Greg

PS Put a length of heat-shrink onto the wire before you join them. Use Mrs Darkhorse's hair dryer to shrink the tubing. Don't get flux on the hairdryer.

Cheers Greg, I got there in the end, but not quite in the above order!! Was pleased with the end result and the bike got me to meeting on time this morning and then to the office

 

[Engineer]

Wow.
This is the longest thread about sticking a couple of wires together that I've ever seen

(although the technical stuff about controller area networks is very interesting)

It is complex stuff and most 'old timer' mechanics understandably have trouble getting their heads around this stuff, because you can no longer just 'hit wiv an 'ammer' or weld a few bit of metal together to make it work - and they are quickly out of their depth.

I get out of my depth pretty quickly with the mechanical stuff, not least because I don't have the training or the tools - so I will always defer to the mechanical experts; but I have been doing electronics manufacture, software, production engineering and design for almost 40 years so do know a little bit about it.

 

[Engineer]

you will if you short two wites together that run to switch - you might not generate the bit stream, but the controller will generate it for you when your short pulls up / down the corresponding input to the controller.

Yes exactly - so better to have the power disconnected when working on the circuit.

 

[Bear]

Ah, nostalgia. Apologies that the technical content probably resembles gibberish...

Technical content resembles knowledge and understanding. I've no experience of Canbus but I remember when Ethernet used a cable as thick as a broomhandle but bright yellow. Your description of Canbus makes perfect sense.

 

[ahutcheon]

Technical content resembles knowledge and understanding. I've no experience of Canbus but I remember when Ethernet used a cable as thick as a broomhandle but bright yellow. Your description of Canbus makes perfect sense.

Me too, and Cambridge ring was a plausible alternative for a while...

One of the neat things about CAN is that it's collision sense multiple access, rather then ethernet's collision detect. Packet start is synchronised, and the output driver design means that a node pulling the bus low prevents any other node pulling the bus high. Transmitters monitor the bus state, so drop out of arbitration silently if they try to send a high bit but read back low. Which gives priority based message transfer on a shared bus, so you can use rate monotonic scheduling theory and its more sophisticated friends to analyse how long a message will take to actually get sent.

So don't connect anything to the CAN bus unless it only listens: something that attempts to send will mess up message timing even if it doesn't use a message id that already belongs to another ECU.

But soldering wires is fairly safe if you're sensible...