USB Diagnostic Board: What Connectors To Include? - Page 1
Forum section: electronics / general

author: EPAIII
author_rank: Super Contributor
timestamp: June 27, 2023, 10:40:29 am
content: I am making a USB Diagnostic PCB. It will be an in-line device where I can scope the signals, interrupt the signals, connect the lines on either side to Hi or Gnd, and perhaps more. I plan to have two of the various types of USB connectors, one on each side of the board with switches between and test points on both sides so I can scope either end of the cable to see what both connected devices are doing.I do not plan to have more than five pins connected: just using the basic four and I am not completely sure what to do with the fifth yet. There is a lot more reading to do. And I am not going to worry about speeds. This is mostly for the earlier, slower versions of USB. But it may get pressed into higher speed circuits. As it is a diagnostic tool, I am not sure on that.What I want some input on is the types of USB connectors to include. So far I have started an order that includes types: A, B, B-mini, B-micro, and C. The type C is presently going to be an Arifruit 5180 Simple USB C Socket b/o board which only brings those five basic pins; none of the others.I do definitely want to include that type C along with the A and B types. I am not so sure about the A and B mini and micro versions, some of which are listed as "deprecated".When I said "in line device" above I meant that it would be placed between two USB devices where a single USB cable with the same or different connectors would normally be.I intend to look through all my devices for guidance on which to include, but any ideas or suggestions would be appreciated.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2023, 11:27:50 am
content: This isn't going to go well. Even at USB 1.1 'Full-Speed' (12 Mbps), signal integrity is important and D+/D- need to be routed as a controlled impedance differential pair to within a few cm of the host or device USB controller, minimising or preferably avoiding any stubs, length mismatch or extra capacitance. Seehttps://resources.altium.com/p/routing-requirements-usb-20-2-layer-pcbGiven that you want to use this breakout for diagnostic purposes, the idea of introducing a bunch of stubs to provide different connectors in parallel doesn't seem like a good idea. Using USB micro-B connectors on your breakout and *short* adapter cables either side of it is far more likely to do what you want. If I had to do a hack job, I'd cut up some USB cables to get the ends I wanted, fit female DuPont connectors on the cut end, and simply put 0.1" pitch pin headers on the breakout board, taking care to keep D+ and D- adjacent and in between Vbus and Gnd in the header pin order.

author: ataradov
author_rank: Super Contributor
timestamp: June 27, 2023, 03:32:30 pm
content: Also, with Type-C it is electrically impossible to make an in-line cable tap with connectors. You will end up with a board that works only with certain orientation of cables. It may not be an issue for a test device though, you will just have to keep that in mind when using it.

author: EPAIII
author_rank: Super Contributor
timestamp: June 27, 2023, 11:07:07 pm
content: And that is precisely why I took the trouble to state that it is to be used as a test or diagnostic device only.Quote from: ataradov on June 27, 2023, 03:32:30 pm

author: EPAIII
author_rank: Super Contributor
timestamp: June 27, 2023, 11:26:25 pm
content: OK, good sanity check. I just gotta start going to bed before 3AM. Thanks a million!You mention two types of connectors for my board; female DuPont connectors and USB micro-B. Assuming I could use either, which would stand the best chance of preserving signal integrity?And I have never hacked into a USB cable. What are the chances that the conductors will work in what you call a "DuPont" style, header connector that was intended for ID attachment to standard ribbon cable?I DO see that the kit you suggest uses crimp pins, not iD style. That kit is inexpensive and I think I have tools to crimp the pins so I may get it in any case.Quote from: Ian.M on June 27, 2023, 11:27:50 am

author: thm_w
author_rank: Super Contributor
timestamp: June 28, 2023, 09:10:00 pm
content: Your idea will work fine for robust and low speed devices for testing.For the type C you can use a 12-pin type C connector which is easier to solder. You'll lose access to all those extra pins, which you probably don't care about.Here is a module I've used in the past:https://www.aliexpress.us/item/3256801708764885.html

author: EPAIII
author_rank: Super Contributor
timestamp: July 04, 2023, 03:27:54 pm
content: That looks great. Thanks, I think. I plan to connect two of them with mini toggle switches and probably at least one threaded spacer. Then it looks like I can add some header pins on each of them. Then if I can find a way to tack on some test points and I will have my USB diagnostic device.I just had my first experience with AliExpress and it was not fun. At least two hours to order several of that device, some switches, and some test points to add to the boards. But I suppose it saved me the time and trouble of designing my own PCB.So, yes, THANKS! And thanks for all the other responses as well. It will be a while for the delivery from China, but I will try to remember to post a photo when it is all together.Quote from: thm_w on June 28, 2023, 09:10:00 pm