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I have a PCB with some connectors and wanted to identify which type there are of.

How do the experts approach the problem, to identify the type?

For example, the picture below shows a connector, obviously written CAN on it. So it seems easy to say, it must be a CAN Bus. The L and H could be CAN-High and CAN-Low, - maybe for Ground and + for Vcc. So it already turns into guessing.

enter image description here

If you look into the CAN Bus specification, maybe on automotive part, there are always much more wires than just these 4. So is it really a CAN Bus?

Another one:

If you look closely, there is BUS written on it, so good indication for a BUS connector. When searching around the internet, BUSes which wires are sometimes labelled A or B, may lead to the idea, it maybe a RS485 Bus connector. But this is again a wild guess. Also it seems that many companies, label + and - or A and B differently, from what i read so far.

If this is really a RS485, why it has 4 wires, the only types I could find are 2 wired or 4 wired, but the 4 wired has actually 5 wires in the schematic description TD+,TD-,RD+,RD-,GND. Again confusing.

enter image description here

So is there an expert approach or best practice for identifying connectors or electric components in general or is this only possible by experience?

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  • \$\begingroup\$ Experts will use the schematic of the circuit board and the BoM. \$\endgroup\$
    – Andy aka
    Jul 26, 2020 at 8:56
  • \$\begingroup\$ off course the schematic and BoM does not exist \$\endgroup\$
    – gantners
    Jul 26, 2020 at 12:08

1 Answer 1

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CAN bus needs only 3 wires 2 signals and a ground so a 4 wire terminal with an added power terminal seems plausible. the two transistors and two large 120-ohm resistors are also consistent with a CAN driver

The second one probably is RS485, you can see that the traces for + and - are wide and come from elsewhere on the board, so they are probably power terminals.

Check the part number on the SO8 that's behind the terminals, Im expecting that that's an RS485 driver.

As for how to be sure: figure out what parts on the board are connected to which the terminals on the connector.

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  • \$\begingroup\$ Thank you, is there any reliable source on the internet which gives a great overview about connectors/buses and their accompanying components, like CAN is at the end of the line terminated by 120 -ohm resistors? \$\endgroup\$
    – gantners
    Jul 26, 2020 at 12:11
  • \$\begingroup\$ Pinouts.ru is sometimes useful. but that just says which terminal is which. wikipedia has pointers to the stanadrds documents, and often useful overview information too. \$\endgroup\$ Jul 26, 2020 at 12:16

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