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I have a PCB that has USB OTG on it, and I use it to update my PCB firmware. It is USB 2.0. Now I wanted to do it through pogo pins, and I was thinking of skinning the cable and soldering the data lines and ground to the pogo pins. However, I know that USB cables are shielded, and my pogo pins are not. I thought of adding ferrite toroids around them, but there is not enough space in between the pins. Would this possibly create a problem, and should I get shielded pogo pins, or could it be viable and work without them? I know that trying is a way to find out, but I believe it is better to think first and then do.

Cable length is about 1 meter, and pogo pin is some generic Chinese pogo pin, approximately 4cm length. Speed is 480mbit/sec

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  • \$\begingroup\$ what is the length of the cable you are planing to use, also share more info about pogo pin you are referring to please \$\endgroup\$
    – User323693
    Commented Aug 26, 2019 at 10:11
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    \$\begingroup\$ What speed? Are you trying to hit high speed (480mbit/sec) or full speed(12mbit/sec)? \$\endgroup\$
    – Lior Bilia
    Commented Aug 26, 2019 at 10:22
  • \$\begingroup\$ @LiorBilia 480mbit/sec \$\endgroup\$
    – Willy Wonka
    Commented Aug 26, 2019 at 10:53
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    \$\begingroup\$ Are you sure? What makes you confident that speed is used? As for your goal, it is out of spec but might work, at least until it doesn't. You could build it and also try it with some extension cables in the hope they would increase any problem to give you an idea of the margin when used without. What are the consequences if it "only works sometimes?" \$\endgroup\$
    – Chris Stratton
    Commented Aug 26, 2019 at 11:46
  • \$\begingroup\$ Also if you plug a high speed device into a full speed host or hub, it will typically run at full speed. Only rare incomplete implementations or timing critical uses would likely fail. How big is the firmware update? Sometimes you can make a PC full speed by not loading the high speed mode core driver on OS startup. \$\endgroup\$
    – Chris Stratton
    Commented Aug 26, 2019 at 11:47

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What works in practice?

On most desktop PCs, USB 2.0 ports on the front/top of the case are connected to the motherboard via a cable terminated with standard 0.1" connectors. Notice there is about 1-2cm of exposed unshielded wire, and 0.1" headers are not really "high-speed"...

enter image description here

The USB connector shield can make contact with the metal case, for shield continuity, but it is not always the case. Sometimes it's all plastic everywhere and it still works. I'm not sure about EMI certification though...

enter image description here

I don't think your pogo pins will be worse than this abomination... And there are zillions of motherboards working without trouble using just that... Real-world tested!

I'd rather use the USB ports at the back of the PC as these are directly mounted on the motherboard, in order to avoid culumative signal degradation from the 0.1" headers and wires on top of the pogo pins.

If this does not work I'd try to solder the pogo pins on a USB male connector and plug that into a hub directly without using a cable. A few cm long USB connection (between the hub chip and your board) without extra cable length should be short enough to reduce transmission line effects substantially.

I'd also program the microcontroller with a USB2 bulk echo program, then use libusb on the PC to transfer lots of data back and forth, let it run for a few hours, check if it works, how fast it is, add some extender cables to degrade the signal to see what margin you have, etc.

Note the loose wires are no longer an option for USB 3.0... but it still uses 0.1" headers!

enter image description here

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There are full spec USB 3.1 Pogo Pin connectors from vendors like CCP Contact Probesenter image description here

They have a plug tail which u can either solder into a pcb or solder it to shielded cables. The alternative are magnet connector cables, that you can get from alibaba or amazon. Some of them have the full USB 2 spec.

Also an option, if you want to go really fast is the new thunderbolt 3 connector from innerexile

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There are coaxial pogo pins, however, they are matched to 50 Ohm single ended, while you need 90 Ohm differential. Your best option, assuming you absolutely have to maintain 480mbit/sec data rate is to use 2 50 mil pogo pins at ~2mm pitch, for the data, and as many pogo pins for ground, around them. Keep the cable as short as possible, with no hubs along the way.

If your design actually requires just full speed, then any 75 or 100 mil pogo pin will do the job.

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  • \$\begingroup\$ This is overkill for 480 Mbps USB-HS for a connector within a couple of inches of the PHY. You can use pretty much any connector with no special design attention and it will be fine. Your advice would be on point for 5 Gbps USB-SS. \$\endgroup\$
    – pericynthion
    Commented Jan 22, 2020 at 5:08
  • \$\begingroup\$ @pericynthion: The circle of ground pins is not only for impedance matching, but also to make sure ground makes contact before data \$\endgroup\$
    – Ben Voigt
    Commented Apr 28, 2023 at 19:13

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