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I have wired some custom USB-C cables from scratch in the past, where the USB-A connector is plugging in to a host PC. If I wired a USB cable where the USB-C connector was plugging into a host receptacle (a USB-C to Mini-USB cable for example), would there be any additional wires/pins that need to be connected in order for the cable to function properly? Typically, I am using a 4-wire cable, connecting VBUS, Ground, D+ and D- pins.

Thanks in advance!

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2 Answers 2

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If you want the cable to act as Type-C host to mini-B plug (to plug into a device with mini-B receptacle), you should connect A5 pin to ground via 5.1k 5% resistor inside the Type-C overmold. This will inform the Type-C host that the cable is "a device". Although the mini-B is not in the official list of allowable cables in Type-C specifications, you can use the wiring schema for Typ-C to micro-B plug, it is there, and mini-B is one-to-one wired to micro-B.

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  • \$\begingroup\$ I may not be able to do this with the connectors I have, not sure. Here is a picture of what I'm working with: imgur.com/a/RSkxc Wiring directly to the tiny pin may be an option, but I don't trust my hand steadfastness enough for that :) \$\endgroup\$
    – rockwell
    Oct 2, 2017 at 19:24
  • \$\begingroup\$ @rockwell, this connector-interposer should already have footprints for 0603 SMT chip resistors, for two options - for a "host end" (5k1 to ground), and for "device end" (56k to VBUS). Do some reverse engineering of this little PCB. \$\endgroup\$ Oct 2, 2017 at 19:40
  • \$\begingroup\$ Yes, the connector has two little SMT chips already on there (with one empty), but frankly I don't understand what they do. I guess that's part of what I'm trying to understand. \$\endgroup\$
    – rockwell
    Oct 2, 2017 at 19:56
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Those two little SMD chips or rather the left one (the one on the right is a capacitor and can be ignored) is how a device detects what type of connection is supported when plugging it in.

Think of it as the USB-C equivalent of the hardware style Master/Slave config on old IDE Hard drives where one of a group of 3 2x1 header pins was jumpered to set the drive into either Master, Slave or Cable Select mode.

What ale-chenski means in his last comment is that the connector pcb in question was made with your use-case in mind; To reconfigure it into a Host-type start by measuring the resistor already on the board (very likely to be a 56kOhm) as well as which pins both pairs of pads connect to (measure between the pad on the connector side and the pins themselves).

Doing these two steps is what he means (I believe ^^) by reverse engineering the pcb since you need to know both in order to be able to remove and/or replace the current resistor with a new 5.1kOhm one connected to the appropriate pin (A5).

Hope this doesn't leave you with more questions than before at least.

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