Myke Rocks
Registered user
This document is a preliminary for anyone working on a BMW R1200 & is in regard to the Canbus system & the worries one may have in regard to making modifications.
I have, in this document, referred to the CPU as “Canbus”. This is a misnomer, but, for the purposes of working on the bike, I will use this incorrect term, since this is how most people refer to the group of CPUs which make up the network.
I wished to try and modify (Slightly) the Canbus wiring associated with the desire to have auxiliary driving lights which came on & off with main beam, also were switch controllable. Since I have an R1200RT, There is nowhere neat on the bike to fit an auxiliary switch.
I therefore bought an Autoswitch along with a set of PIAA lights from the States.
Lights were compact, but not very good, &, as supplied, fouled the front guard. I moved the pivot holes up 10mm & this fixed that problem.
I fitted the Autoswitch & it worked until the fuel pump SSR started to go faulty. It then started randomly switching itself off.
As you will see from my other documentation on the subject, the Autoswitch is prone to interference from harmonics generated by devices round the bike E.G. Fuel Pump SSR, HDI lights.
I started to investigate how BMW sends signals to the Canbus system, & discovered a very robust system which is not prone to interference, or to damage by people doing silly things with it.
Thus:
All signals E.G switches into the Canbus system, which we shall call inputs, are individually supplied from the Canbus system with a 12v +ve via a resistor.
As a consequence, when not connected to anything, a voltmeter will show 12v+ at any input. To send a signal to the Canbus, the input is grounded to 0v.
So, whether you connect 12v to the input from a battery, or 0v from ground, you cannot do any harm.
Once one recognises this, one realises that it is practical to connect up a realy or timer in parallel to any input. E.G Indicator canel. The Coil +ve comes from the Auxiliary socket power supply, & the -ve from the cancel switch circuit. When the cancel button is pushed, the relay ernergises, without interfering with the signal to the canbus system.
I have not “played” with the outputs from the Canbus system other than to discover they are internally & closely protected from overload (much to my annoyance), so I cannot comment on their properties.
Regards:
Michael
I have, in this document, referred to the CPU as “Canbus”. This is a misnomer, but, for the purposes of working on the bike, I will use this incorrect term, since this is how most people refer to the group of CPUs which make up the network.
I wished to try and modify (Slightly) the Canbus wiring associated with the desire to have auxiliary driving lights which came on & off with main beam, also were switch controllable. Since I have an R1200RT, There is nowhere neat on the bike to fit an auxiliary switch.
I therefore bought an Autoswitch along with a set of PIAA lights from the States.
Lights were compact, but not very good, &, as supplied, fouled the front guard. I moved the pivot holes up 10mm & this fixed that problem.
I fitted the Autoswitch & it worked until the fuel pump SSR started to go faulty. It then started randomly switching itself off.
As you will see from my other documentation on the subject, the Autoswitch is prone to interference from harmonics generated by devices round the bike E.G. Fuel Pump SSR, HDI lights.
I started to investigate how BMW sends signals to the Canbus system, & discovered a very robust system which is not prone to interference, or to damage by people doing silly things with it.
Thus:
All signals E.G switches into the Canbus system, which we shall call inputs, are individually supplied from the Canbus system with a 12v +ve via a resistor.
As a consequence, when not connected to anything, a voltmeter will show 12v+ at any input. To send a signal to the Canbus, the input is grounded to 0v.
So, whether you connect 12v to the input from a battery, or 0v from ground, you cannot do any harm.
Once one recognises this, one realises that it is practical to connect up a realy or timer in parallel to any input. E.G Indicator canel. The Coil +ve comes from the Auxiliary socket power supply, & the -ve from the cancel switch circuit. When the cancel button is pushed, the relay ernergises, without interfering with the signal to the canbus system.
I have not “played” with the outputs from the Canbus system other than to discover they are internally & closely protected from overload (much to my annoyance), so I cannot comment on their properties.
Regards:
Michael
