My USB panel mount receptacles metal body is connected to the ground pin.
If I twist DM and DP wires together and the USB.VBUS and USB.GND together can I just connect the USB ground wire to the ground pin on my receptacle?
Or do I still need to use shielded cable? I should add the receptacle will be housed in plastic so no contact with the car ground system.
And if I do need shielded, it should only be connected at the ADU end, correct? So 3 core and shield with the shield connected to the USB.GND pin at both ends?
To the ground or shield pin?
A proper USB socket should have five connections.
Two contacts for 5V and ground.
Two contacts for data wires.
And outer metal should be connected as a shield.
Can I not just used twisted pairs without a shield? The other issue I have found is that all the ‘pre cabled’ USB sockets have conductors too small for secure crimping in the ADU connector pin terminals.
I was wondering if I could just use 2x twisted pairs for the data, 2x twisted pairs for the supply and ground. Shouldn’t that reduce any interference?
There are sockets like you posted, but with five pins instead of 4.
You can try without a shield, but it’s impossible to tell if it will work reliably.
It depends on the overall harness design and electrical interference sources.
The only way to know is to test.
P.S.
Twisting and shielding are not interchangeable.
Those are ways to minimize two different noise coupling modes.
Twisting removes inductive coupling (fast current changes, magnetic fields).
Shielding is removing capacitive coupling (fast voltage changes, electric fields).
What I mean is, do people commonly run separate wire to a separate USB connector?
Or use a pre wired USB socket? If so, any recommendations?
Or something else?
It looks like I’ll need to buy some more parts so I want to make sure I get the right ones.
We use these micro SD card readers. They work excellent for the USB logging. The whip is about 36 inches long, just cut off the USB connector and wire direct to the ADU or ECU. Format the card correctly and you are done.
Thanks again. The only issue I’ve run into doing that is that the conductors are too small for the ecu terminals. I’ve been trying to find some with at least 0.75mm conductors but no luck so far.
I tried crimping them but even on the smallest crimp setting I was still able to separate them from wires without too much difficulty.
Looks like I’ll need to make up a mini loom with 4 core shielded 0.75mm cable and a USB A female socket.
So, to be clear, connect the 4 cores to the respective ADU pins (with no shield connection), then at the USB socket connect the 4 cores and the shield to the shield terminal?
I know the shield must only be connected at one end so as not to induce a voltage on the shield wiring, but I thought it should be connected at the ‘host’ end, which in this case would be the display would it not?
Thanks to this discussion, I noticed something I hadn’t considered before.
The best connection will depend on the flash drive itself.
According to the USB specification, the host device should provide shield termination (ECU in this case). However, manufacturers of USB devices don’t always follow these rules.
For example, I have two flash drives from SanDisk.
One has a plastic case, including the outer shell of the connector.
That means there is no shield connection for the flash drive itself.
The second one has a metal case, which is also the connector’s outer shell.
This flash drive has an internal connection of the ground pin and the outer shell for shielding.
Safe connection method that will work with any flash drive:
No requirements for the flash drive.
Ground and shield must be connected together at the USB socket side (might not be possible with USB sockets that are molded together with the cable).
Shield on the ECU side must be floating (not connected to anything)
The best connection method:
It requires a flash drive without an internal connection between the ground and the shield.
The USB socket cannot have an internal connection between the ground and the shield.
The shield must be connected to the power ground on the ECU side.
The shield must be connected to the outer shell of the USB socket (there is no connection between the shield and the ground on the flash drive side).
If your pen drive does not have an internal connection between ground and shield (you can check with a continuity test), connect the shield wire to the power or main ADU ground (Pin 22 or 23).
If your pen drive does have internal connection between ground and shield you have to leave the shield floating on the ADU side. It will be connected to ground through the drive.
Thanks for the reply, however I am still confused.
I have now bought a 2nd ‘5 pin’ version of the 4 pin one above you recommended I didn’t use.
If I understand you right, the 4 pin version I can use as per your ‘safe method’ if I connect the shield and ground together at the USB adapter end and leave the shield disconnected at the ADU end. Is this correct?
If I use the 5 pin version, I connect it as per my image? Is that correct?
Any chance you could put up a drawing showing both the 4 and 5 pin connections for clarity?
@mkuklis_ECUMASTER
Can you please advise on the images I posted? I should have the parts arrive tomorrow or Friday and want to get the job done at the weekend.
