Read differential signal through induction? - Page 1
Forum section: electronics / projects

author: mayor
author_rank: Regular Contributor
timestamp: October 22, 2023, 01:23:44 pm
content: Hi,I'm interested in reading a differential signal (CAN bus) without having to splice wires. Something like:https://mechatronics.by/wp-content/uploads/2018/07/InCAN_en.pngNot too sure what the best approach is. Any help or reference circuits appreciated!

author: moffy
author_rank: Super Contributor
timestamp: October 22, 2023, 01:45:12 pm
content: According to the patent in russian:https://patentimages.storage.googleapis.com/19/d3/1c/b507c68a6f1488/RU2446604C1.pdfIt looks like they use two capacitive sensors, one for each of the wires but it is patented so there could well be legal ramifications to what you are attempting.

author: mayor
author_rank: Regular Contributor
timestamp: October 22, 2023, 02:24:12 pm
content: Hah, my russian's a bit rusty!

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 22, 2023, 07:23:38 pm
content: I don't know how much of that you can patent anyway, but if you read it carefully, I think you should find a way to circumvent it. It's a russian patent anyway, not sure it covers any other country. Or if you should even care, if you don't intend to make this a product.It looks pretty simple.But your initial idea was inductive, and so you could go that path instead indeed, for instance by wrapping a couple turns of wire around each CAN wire and some conditioning circuit.

author: mayor
author_rank: Regular Contributor
timestamp: October 22, 2023, 08:03:51 pm
content: Quote from: SiliconWizard on October 22, 2023, 07:23:38 pmYeah, I'll experiment a little, I think. I can't make much of that russian patent, not sure I care to google translate it.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 22, 2023, 08:40:01 pm
content: The english text is already available;https://patents.google.com/patent/RU2446604C1/en

author: fourfathom
author_rank: Super Contributor
timestamp: October 23, 2023, 03:10:05 am
content: You might try a wideband ferrite clamp-on core with the CANbus wires passing through it in opposite directions (a differential current-sense), with a multi-turn secondary winding, resistive load, going to your monitoring system. Depending on the frequency response of the current-transformer you might need some de-emphasis filtering to give you a usable signal.

author: mayor
author_rank: Regular Contributor
timestamp: October 24, 2023, 06:31:52 pm
content: Change of plans :-) I want to also write on the bus after all. Taking a chance that _someone_ might recognize this connector (attached) from the following videohttps://youtu.be/ISvH6xe-usE?si=vKFKg4PYAlkGwttR&t=384. I'd ideally find some sort of Y-Cable.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 24, 2023, 10:24:07 pm
content: It reminds me of JST connectors.I know BMW uses a number of Deutsch connectors in their cars:https://www.deutschconnector.com/products/deutsch_connectors/but I couldn't find this particular one in their catalog. (But you can have a look, may have missed it.) You'll probably reccognize other connectors under the hood though.As I said, it looks like the kind of connectors JST would make - haven't found this exactly in the JST catalog either, but haven't spent much time on it. So, something to look at as well.

author: mayor
author_rank: Regular Contributor
timestamp: October 25, 2023, 01:44:29 am
content: Whoa! That's a trip back to 1995!

author: Terry Bites
author_rank: Super Contributor
timestamp: October 30, 2023, 04:53:11 pm
content: A differential signal pair will cancel electric and magnetic fields. A shielded cable hides emissions even further. But not perfectly.To exploit the imperfect balance, make a simple down converter, couple it to an SDR dongle, snoop with a small antenna. Get SDR# and its data plugins.Orwww.semanticscholar.org/paper/A-Coreless-Current-Probe-for-Multicore-Cables-Liu-He/0d1c3f4c700862538d71b3bb2b8dbaadbab3bfc1