CANBUS question
Discussion
For Christmas my wife bought me a DAB radio adaptor and paid for it to be fitted to my Skoda Superb estate (AKA Dogmobile)
When I got home I realised that the adaptor is only live when the ignition is in the full ’on’ position but doesn't work with the key in the auxiliary position.
I rang the fitting centre and spoke to the technician who said the DAB adapter unit can't stay on as the power is cut by the CANBUS unit and he can't connect it unswitched as it would drain the battery. It was only later thinking it through that I realised if he had taken the power supply from the same source as the radio then it must sty on with the radio.
Still unhappy I called at the fitting centre this morning and they are adamant that they cannot get an auxiliary switched supply for the unit.
I just cannot believe this. As I pointed out to him, the radio stays on when the key is in the auxiliary position as does the cigar lighter so why not utilise those circuits. He says they can’t and the CANBUS unit only uses 4V.
Please tell me this is BS or my head will explode.
I know I'm old school and my knowledge of electrical circuits is limited but…
When I got home I realised that the adaptor is only live when the ignition is in the full ’on’ position but doesn't work with the key in the auxiliary position.
I rang the fitting centre and spoke to the technician who said the DAB adapter unit can't stay on as the power is cut by the CANBUS unit and he can't connect it unswitched as it would drain the battery. It was only later thinking it through that I realised if he had taken the power supply from the same source as the radio then it must sty on with the radio.
Still unhappy I called at the fitting centre this morning and they are adamant that they cannot get an auxiliary switched supply for the unit.
I just cannot believe this. As I pointed out to him, the radio stays on when the key is in the auxiliary position as does the cigar lighter so why not utilise those circuits. He says they can’t and the CANBUS unit only uses 4V.
Please tell me this is BS or my head will explode.
I know I'm old school and my knowledge of electrical circuits is limited but…
The dash cam in my Skoda Octavia is powered from a switched 12v feed. The cam is designed to be run from the lighter socket, but in my car they are 'always live' so I had an auto mechanic fit an additional lighter socket behind the dash with a switched feed. The dash cam now never moves but only records when the ignition is on.
So it is possible but the installer may not have wanted to fit additional non standard wiring.
Edit: missed the fact that the DAB unit seems to draw power from the car's CANBUS system, where CANBUS is involved I tend to give up, it makes things so much more complicated.
So it is possible but the installer may not have wanted to fit additional non standard wiring.
Edit: missed the fact that the DAB unit seems to draw power from the car's CANBUS system, where CANBUS is involved I tend to give up, it makes things so much more complicated.
Edited by GoodDoc on Monday 30th December 10:56
I think they are correct.
There is no ignition feed to the radio, not from my experience with VWs, they use CANBUS, ie the radio is told to turn on via the electronics. It doesn't turn on because it has received a second live 12v when the ignition is turned on.
They can supply a feed when the ignition is on, this is an extra wire they would have installed, but it is live with the ignition on, i.e., fully on, not on the auxillary position.
There is no ignition feed to the radio, not from my experience with VWs, they use CANBUS, ie the radio is told to turn on via the electronics. It doesn't turn on because it has received a second live 12v when the ignition is turned on.
They can supply a feed when the ignition is on, this is an extra wire they would have installed, but it is live with the ignition on, i.e., fully on, not on the auxillary position.
I have recently upgraded the head unit/speakers etc in my A3, and what the fitting centre are telling you is unfortunately correct.
The standard headunit uses the ECU to be told when to be on or off, not a 12v feed, an aftermarket one can't do this. Therefore the ignition live wires are only live when the ignition is on, not in the auxilary position.
It can be wired by piggybacking on the ECU fuse, allowing you to listen whilst the car isn't running, however in mine that requires all the electrics to be on, as the key is basically in the on position. The blower motor/glowplugs etc would all be live, so I now don't listen unless the engine is running.
Out of interest how many positions does your key have? Mine only has On or Off as permanent positions that the key can rest in, the third is "Start" but the key can't be left there obviously, so there is no auxillary position?
The standard headunit uses the ECU to be told when to be on or off, not a 12v feed, an aftermarket one can't do this. Therefore the ignition live wires are only live when the ignition is on, not in the auxilary position.
It can be wired by piggybacking on the ECU fuse, allowing you to listen whilst the car isn't running, however in mine that requires all the electrics to be on, as the key is basically in the on position. The blower motor/glowplugs etc would all be live, so I now don't listen unless the engine is running.
Out of interest how many positions does your key have? Mine only has On or Off as permanent positions that the key can rest in, the third is "Start" but the key can't be left there obviously, so there is no auxillary position?
Yep I also believe the installers are correct. In my 2002 Audi A2 there's also no switched live.
It was slightly complicated but I solved it with an additional relay and a hidden toggle switch when I fitted an aftermarket headunit.
The relay switches a permanent live to the radio, in position 1 on the switch the radio comes on with the ignition fully on, flick the switch and the radio is on. Note just like your DAB adapter the aux position on the key doesn't turn on the radio.
Another possibility might be if there's an amp control wire on the factory headunit that is live when the headunit is on this could be used to switch a relay to power the DAB adapter.
One of the advantages of not having a separate switched live is you'll find the factory headunit will switch off with the ignition, but if you then press power on the headunit without the key in the headunit will turn on, usually for a preset time.
It was slightly complicated but I solved it with an additional relay and a hidden toggle switch when I fitted an aftermarket headunit.
The relay switches a permanent live to the radio, in position 1 on the switch the radio comes on with the ignition fully on, flick the switch and the radio is on. Note just like your DAB adapter the aux position on the key doesn't turn on the radio.
Another possibility might be if there's an amp control wire on the factory headunit that is live when the headunit is on this could be used to switch a relay to power the DAB adapter.
One of the advantages of not having a separate switched live is you'll find the factory headunit will switch off with the ignition, but if you then press power on the headunit without the key in the headunit will turn on, usually for a preset time.
The radio will be getting a permanent 12v feed. Canbus tell it when to switch on.
To be clear the radio does not have a switched 12v power feed. On a Merc I get around this using power off the back of the cigarette lighter which is switched.
Sounds like the fitter has used a clever box that takes a feed off the canbus circuit, and probably integrates the steering wheel buttons also.
To be clear the radio does not have a switched 12v power feed. On a Merc I get around this using power off the back of the cigarette lighter which is switched.
Sounds like the fitter has used a clever box that takes a feed off the canbus circuit, and probably integrates the steering wheel buttons also.
I had this issue on my Audi - partially solved by buying a canbus interface like this -
http://www.ebay.co.uk/itm/Universal-Can-Bus-Interf...
- I say partially because the "ignition" doesn't properly replicate the OEM signals. It does generate a live when IGN is on however. The bit it doesn't do is that the OEM radio stays in if you turn off the engine and leave the key in place - the interface doesn't do that.
The reason is that the interface "senses" the Ign on state by voltage drop rather than using the CAN BUS signals. The "key in" aux is switched in the ign key barrel and feeds back to the CAN BUS module - but I am reluctant to tap into that as (as your installer observed) it's low voltage low current and interfering with it could bugger it up.
We really need a manufacturer to a proper job on the interface - that signal must be available on the CAN BUS, but I haven't been able to find a supplier to do this.
http://www.ebay.co.uk/itm/Universal-Can-Bus-Interf...
- I say partially because the "ignition" doesn't properly replicate the OEM signals. It does generate a live when IGN is on however. The bit it doesn't do is that the OEM radio stays in if you turn off the engine and leave the key in place - the interface doesn't do that.
The reason is that the interface "senses" the Ign on state by voltage drop rather than using the CAN BUS signals. The "key in" aux is switched in the ign key barrel and feeds back to the CAN BUS module - but I am reluctant to tap into that as (as your installer observed) it's low voltage low current and interfering with it could bugger it up.
We really need a manufacturer to a proper job on the interface - that signal must be available on the CAN BUS, but I haven't been able to find a supplier to do this.
Edited by V8forweekends on Monday 30th December 13:12
Edited by V8forweekends on Monday 30th December 13:13
As said about 10x up there^^^ modern cars just use a battery positive feed and use a CAN bus data packet to trigger slave devices into a "ignition on" status (replacing the hardwired "KeyLine" 12v signal for ignition on that used to come from a switch on the ignition key barrel switch).
As such, slave devices, such as the radio, are permanently feed with power directly from the vehicle battery, and power themselves up (and down) based on receiving the correct command over the CAN bus (which is a DATA only bus, i.e. you cannot take "power" off it)
Some radio units do have a switched output available to power up remote devices like CD players and the like, which would be one option (if available on your unit)
Alternatively, you could connect your DAB adaptor directly to a Battery positive source, and whilst this will result in it being powered up the whole time, the actually power draw will, most likely, be minimal.
(if you regularly leave you car unused for weeks at a time it could be an issue, but not for a few days here and there)
You could also get them to fit a subtle manual "on/off" toggle switch somewhere up under the dash, which you leave on most of the time, but turn off if you ever park your car up for weeks (like at an airport when on a 3week holiday etc)
As such, slave devices, such as the radio, are permanently feed with power directly from the vehicle battery, and power themselves up (and down) based on receiving the correct command over the CAN bus (which is a DATA only bus, i.e. you cannot take "power" off it)
Some radio units do have a switched output available to power up remote devices like CD players and the like, which would be one option (if available on your unit)
Alternatively, you could connect your DAB adaptor directly to a Battery positive source, and whilst this will result in it being powered up the whole time, the actually power draw will, most likely, be minimal.
(if you regularly leave you car unused for weeks at a time it could be an issue, but not for a few days here and there)
You could also get them to fit a subtle manual "on/off" toggle switch somewhere up under the dash, which you leave on most of the time, but turn off if you ever park your car up for weeks (like at an airport when on a 3week holiday etc)
I think DAB radios do use a fair bit more battery power than analogue. Seen a lot of comments about home DAB radios wasting the batteries up real fast when I was thinking about getting one for the kitchen, so that could be the thinking behind having ignition full on before powering up. Pity your radio on button doesn't give an hour over-ride like a lot of radios do.
I develop OEM infotainment systems, and as said above, the head unit will have a permanent connection to the battery and will be switched on by a CAN message.
Most cars do have somewhere that a 12v connection can be taken from that is also switched by CAN, for instance in the Fiat 500 you can actually get a switched 12v feed from the head unit. I'm not really au fait with the VAG system, so can't advise if there is somewhere better to take the 12v feed.
I image that the 4v is the voltage on the CAN signal, which is useless for powering anything, it is more of a network cable.
Most cars do have somewhere that a 12v connection can be taken from that is also switched by CAN, for instance in the Fiat 500 you can actually get a switched 12v feed from the head unit. I'm not really au fait with the VAG system, so can't advise if there is somewhere better to take the 12v feed.
I image that the 4v is the voltage on the CAN signal, which is useless for powering anything, it is more of a network cable.
Craikeybaby said:
I image that the 4v is the voltage on the CAN signal, which is useless for powering anything, it is more of a network cable.
Worse than that, if you attach a low impedance current sink to the CAN bus (less than ~60ohms) the bus will fail, and actually prevent the rest of your car from working at all!As such, if we assume a 50:50 mark space ratio, with the nominal +-2.5v voltage the most power you could ever pull from a CAN bus is theoretically just 0.104 Watts, and with that load the bus would fail dominant low.
/CANGEEK
Plenty of switched live feeds in most VAG cars in the fusebox. Any installer with more than half a braincell will know where to pick one up from. Generally (in VWs anyway) the mini-blade fuse terminals are nearly always switched live, but I will admit I've been out of the fitting game for a few years now.
5 seconds of googling suggested this: http://www.briskoda.net/forums/topic/225484-gainin...
5 seconds of googling suggested this: http://www.briskoda.net/forums/topic/225484-gainin...
Max_Torque said:
Worse than that, if you attach a low impedance current sink to the CAN bus (less than ~60ohms) the bus will fail, and actually prevent the rest of your car from working at all!
/CANGEEK
I tried to install a parrot hands free on a CANBUS car and had this. The car just shut down and refused to go. There was an error message on the dash and nothing more. Another frustration is that I took a radio out of one car and put it into another car. Even though they were the same year and same manufacturer it did not work because they worked on different CANBUS protocols. Very frustrating./CANGEEK
h0b0 said:
Max_Torque said:
Worse than that, if you attach a low impedance current sink to the CAN bus (less than ~60ohms) the bus will fail, and actually prevent the rest of your car from working at all!
/CANGEEK
I tried to install a parrot hands free on a CANBUS car and had this. The car just shut down and refused to go. There was an error message on the dash and nothing more. Another frustration is that I took a radio out of one car and put it into another car. Even though they were the same year and same manufacturer it did not work because they worked on different CANBUS protocols. Very frustrating./CANGEEK
h0b0 said:
I tried to install a parrot hands free on a CANBUS car and had this. The car just shut down and refused to go. There was an error message on the dash and nothing more. Another frustration is that I took a radio out of one car and put it into another car. Even though they were the same year and same manufacturer it did not work because they worked on different CANBUS protocols. Very frustrating.
It could also be that the head unit was coded to the VIN of the car, which I think is (or at least was) a Thatcham requirement, I know for some of the head units I have worked on we needed to flash them with special software to move them between development cars.Mr Happy said:
What car was it if you don't mind me asking?
I was taking a radio out of a Dodge Journey and putting it into a Chrysler 300. After looking at eBay I discovered that there was a difference in CAN BUS and so not compatible. I think there was a voltage difference. The 300 being higher. It have the bus error message. I realize this is not UK related but the Chrysler radios pop up in all sorts from lancias to Ferraris (looks bloody horrid in the California and is ridiculed by Hammond in his review)
h0b0 said:
Mr Happy said:
What car was it if you don't mind me asking?
I was taking a radio out of a Dodge Journey and putting it into a Chrysler 300. After looking at eBay I discovered that there was a difference in CAN BUS and so not compatible. I think there was a voltage difference. The 300 being higher. It have the bus error message. I realize this is not UK related but the Chrysler radios pop up in all sorts from lancias to Ferraris (looks bloody horrid in the California and is ridiculed by Hammond in his review)
After numerous misspent years fitting hands free kits and other accessories to all sorts, in my experience it's generally not the CAN side of things that causes the problems. It is ensuring that everything on the bus is still connected when you're finished!
I did have problems with some integration kits that hijack the OEM phone controls for Parrot kits, so stuck to installing the boxed kit with the minimum of 'extras' and achieved greater success in doing so
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