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Associate

Join Date: Jan 2008
Location: Bangalore , India
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Induce Change in Voltage on a Wire

03/01/2016 10:53 PM

Hi

I am working on a bus of DC wires (2 wires ) which is having a DC voltage of 2.5 and 3.5 respectively. (CAN bus)

I would like to send some signals on to the bus without touching the bus.

I am thinking of inducing voltage by changing the field. I am little scratchy on the Electrical side. Require assistance on the same.

Thanks

Franklin Francis

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Pathfinder Tags: automotive CAN bus communication
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Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

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#1

Re: Induce Change in Voltage on a Wire

03/02/2016 4:55 AM

It depends what sort of signal you want to send.
It's easy enough to induce a simple pulse onto the wire if you wrap it round a transformer core and apply a pulse of voltage to another winding on the same core.

Del

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#2
In reply to #1

Re: Induce Change in Voltage on a Wire

03/02/2016 8:14 AM

Hi

Thanks.

But the other end is just a wire. Just plain conductors but not coil.

Please refer the link below.

https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/CAN-Bus_Elektrische_Zweidrahtleitung.svg/220px-CAN-Bus_Elektrische_Zweidrahtleitung.svg.png

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#4
In reply to #2

Re: Induce Change in Voltage on a Wire

03/02/2016 9:55 PM

It is 2 wires, i.e. a shielded twisted pair. And your link shows this. Note the 120ohm termination on each end. Both these wires are floating relative to ground. You can connect a node anywhere along this bus. Is there something your not indicating about where the bus is located, that prevents you from attaching a node?

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#7
In reply to #2

Re: Induce Change in Voltage on a Wire

03/03/2016 2:35 AM

No.. I'm, not going to look at your link.
I gave you an answer... it's up to you to use it rather than just raising another problem or objection.

Del

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#3

Re: Induce Change in Voltage on a Wire

03/02/2016 10:03 AM

Sounds like you're trying to hack gain access into the CAN Bus without having physical access to it. That is difficult to do since it is specifically designed to be highly impervious to the normal electrical noise found in its usual operating environment.

Perhaps you can be more specific as to your goal.

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#5
In reply to #3

Re: Induce Change in Voltage on a Wire

03/03/2016 12:19 AM

Hello RAM

You have exactly pinned my requirement.

I want to hack it without touching the wires.

Thanks

corners

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#6
In reply to #5

Re: Induce Change in Voltage on a Wire

03/03/2016 1:08 AM

There is no practical way of achieving what you want

Give up

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Guru

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#10
In reply to #5

Re: Induce Change in Voltage on a Wire

03/03/2016 8:57 AM

This is the best description I have found of the physical structure of a CANbus:
http://marco.guardigli.it/2010/10/hacking-your-car.html
With a twisted pair wire the idea of radiating a signal to influence the bus signal is a non-starter. You may find that the vehicle OBD-II connector has two pins for the CANbus signal.

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Guru

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#8

Re: Induce Change in Voltage on a Wire

03/03/2016 5:16 AM

CAN bus wires are shielded to prevent normal industrial electrical interference. To hack as you describe would require you to interrupt the shield but if the shield becomes discontinuous then the normal operation will fail. I don't think CAN wiring was originally designed to foil hackers but it is 100% effective in doing so. In generating your post you will have triggered some key words in both the NSA and GCHQ computers (and if your post has not then my reply will have done so). They will relay your intention to the Indian security forces. It may take a few days for the data to be interpreted and distributed but expect a knock on you door at 05.00 one morning soon.

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Associate

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#9
In reply to #8

Re: Induce Change in Voltage on a Wire

03/03/2016 5:43 AM

tell this bedtime story to ur kids

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#11
In reply to #9

Re: Induce Change in Voltage on a Wire

03/03/2016 12:03 PM

In the straight cable, all noise current is flowing in the same direction, just like in an ordinary transformer coil. When the cable is twisted, in some parts of the signal lines the direction of the noise current is the opposite from the current in other parts of the cable. Because of this, the resulting noise current is many factors lower than with an ordinary straight cable.

Likewise, any introduced signal (if you can get past the shielding) without direct contact, would tend to cancel out.

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Associate

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#12
In reply to #11

Re: Induce Change in Voltage on a Wire

03/04/2016 3:22 AM

Thank you ....

your answer is convincing

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