USB Type C connector and cable - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: January 19, 2020, 10:08:33 pm
content: Hi,I am thinking to use a USB type C connectors and cable between two units for a new product. The signals are low speed and the only reason for using this solution is the large number of contacts in a compact connector and relatively flexible cable without making it custom. I want to use it as a straight cable withOUT any ICs, just to transfer signals and few mA of power.1) do USB type C connectors in cables which transfer data (i.e. all pins connected/active) contain electronics or are they just plain simple cables with straight copper wires between the connectors?2) what is the best and simplest (!) way to implement such solution?Thank you

author: wraper
author_rank: Unknown
timestamp: January 19, 2020, 10:23:48 pm
content: There is no electronics in the cable. Be aware that in USB 3.x cables number of actual wires is only half of the total pin count. USB 2.0 cables have only 4. GND wire usually is connected to a shield. Also if you use it, be ready that people will certainly plug something non compatible on the other end like charger, laptop, whatever. So circuit should tolerate such conditions, not blow up.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 19, 2020, 10:46:40 pm
content: Only about half the pins or fewer on the USB-C connector are wired up on any given cable. For instance, the D+ and D- pins are duplicated on the connector, but only one side is wired up. Likewise, the power and ground pins are all connected together in parallel.Also, some cables are USB2 only--they do not have any superspeed pairs. Many USB-C chargers come with this kind of cable only intended for charging. Other cables may have 2 or 4 pairs present.One of the two CC pins is normally wired through, but there are electronically marked cables in which case there will be a chip hanging off the CC pin (and powered by the "other" CC pin). All cables supporting USB 3.1 or higher, supporting alternate modes (like thunderbolt or HDMI) or 5A charging need to be electronically marked.So all you can really guarantee are the basic USB-2 pins: VBUS, GND, D+, and D-. Anything else is going to be at the least more complicated and may not be present in whatever cables you use.Of course, you also want to consider the possibility of someone plugging an arbitrary USB type-C device into yours.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 19, 2020, 11:00:25 pm
content: Oh, you said "product" -- I would not recommend doing this in any sort of product. That is just going to lead to frustrated customers and possibly equipment damage.

author: nctnico
author_rank: Super Contributor
timestamp: January 19, 2020, 11:17:27 pm
content: USB-C connectors are pretty cheap and cables are readily available. I've used a USB-C connector to take a PCIexpress bus to a daughterboard in a price sensitive product. There is one catch though: you can plug a USB C in in any direction and the connection isn't 1 to 1.However for a low speed signals and a small bit of power I'd recommend to use ribbon cable or a crimp style connection. Molex pico-spox, JST XH, etc.

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2020, 05:26:46 am
content: Quote from: nctnico on January 19, 2020, 11:17:27 pmSooooo... you reinvented Thunderbolt??

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2020, 05:34:08 am
content: Quote from: ricko_uk on January 19, 2020, 10:08:33 pmIf there is ONE connector family one should NEVER misappropriate, it’s USB, because you can pretty much guarantee it WILL get connected to an actual USB device or power source, causing it to not work at best, and damaging one or both devices at worst.So I agree with the others who strongly suggest using something else.How many pins do you need?

author: ricko_uk
author_rank: Super Contributor
timestamp: January 22, 2020, 05:51:49 am
content: Quote from: tooki on January 22, 2020, 05:34:08 amThank you Tookiwe need minimum 10 ideally 12 poles. As compact as possible. Connector with sleeve/grip to be inserted and pulled out easily like any consumer cables (Ethernet/USB etc).BTW, we were looking at USB C because we only need to make 60 units. Not a mass market solution. And the cable would be provided with the equipment. Also the entire equipment/system is only on loan.Thank you

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2020, 06:33:16 am
content: Well, for 10 pins I’d suggest a 10p10c modular connector (same as RJ-45 but with more pins). Ethernet is tolerant of being connected wrong, so unlikely to cause problems if connected by accident.Of course, if you could get it to 8 pins or less you could use cheap Ethernet cables.

author: mansaxel
author_rank: Super Contributor
timestamp: January 22, 2020, 06:34:57 am
content: Unless operatedonlyby its builder, I'dSTRONGLYrecommend against using USB connectors.D-sub high-density 15-pole ("VGA") is a better alternative, while also to some extent suffering from the "too familiar" problem. Beyond that, Hirose or similar japanese manufacturers, or a mini-Tuchel (there is a 12-pin) can do the job. Of course milspec connectors like 5015 or KPT are always best. But, at a price.

author: Berni
author_rank: Super Contributor
timestamp: January 22, 2020, 07:03:53 am
content: Quote from: ejeffrey on January 19, 2020, 11:00:25 pmQuote from: tooki on January 22, 2020, 05:34:08 amOh so you mean like using the USB-C connector for different things on different consumer electronics devices? That sounds familiar. By standard USB-C only needs to support USB 2.0 to meet the spec.But if the device so chooses it can also have the flowing:-USB 3.0-USB-PD power delivery(from 5V all the way to 20V 5A, varies on what is supported)-Thunderbolt-HDMI-DVI-MHL (Another digital video format)-Analog video (VGA, Component, Composite...)-DisplayPort-Debug Accessory (Like JTAG)-Analog line level audioYou can plug any two USB-C devices together using a cable, but it will only actually work correctly if both devices support the same features from that list above.So in this regard USB-C is already fucked from the start. Only guarantee is USB 2.0, everything else is a gamble.So if you come up with another feature for USB-C there is nothing really wrong with it because everyone else has already thrown compatibility out the window already. Just make sure you respect the 5V GND and CC pins so that nothing blows up if plugged into a USB-C port.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: January 22, 2020, 09:16:10 am
content: You can always use GND, +5V, D+ and D- up to 5V. But that's only power + two signals, not 14."Universal Serial Bus Specification"Quote

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2020, 11:39:39 am
content: Quote from: Berni on January 22, 2020, 07:03:53 amOh, I totally agree that USB-C is a clusterfuck. But using the connector for something thatisn’t USB or any sanctioned extension to itis asking for trouble.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: January 22, 2020, 12:22:43 pm
content: Quote from: tooki on January 22, 2020, 11:39:39 amNo, it isn't, nothing bad can happen if you only use PWR and D+/-. For example, you can use D+/- as TxD and RxD for a serial port, no problem whatsoever.

author: Berni
author_rank: Super Contributor
timestamp: January 22, 2020, 12:32:20 pm
content: Yep already did combination of USB and UART on MicroUSB before. Just a MUX that switches over the USB data lines over to RX and TX. Since its all 3.3V levels nothing bad happens, adding the usual resistors also makes it survive 5V on those pins.This is pretty much the same as what USB-C does. It muxes over the pins to the appropriate function, except that now doing this is part of the spec. As long as nothing blows up by plugging it into the wrong thing.

author: GromBeestje
author_rank: Frequent Contributor
timestamp: January 22, 2020, 01:35:06 pm
content: Looking at the Wikipedia article,https://en.wikipedia.org/wiki/USB-C#Alternate_Mode_partner_specificationsI'd say "Debug Accessory Mode" seems suitable. it gives 14 pins.

author: senso
author_rank: Frequent Contributor
timestamp: January 22, 2020, 04:09:15 pm
content: How cheap does it need to be?I would go for Harting Push-Pull family, with the 20 pins cables, more than enough pins, robust enough, wont be mis-connected, can use bulkhead connectors on the device side, and then make custom length or buy pre-made cables:https://b2b.harting.com/ebusiness/en/Interface-connectors-PushPull-Device-connectivity-PushPull-Signal/34750?detail=false&sewConfig=falseInquire their rep, and they can show you some more solutions, this would be my approach, given that the end user will surprise you in how dumb they can be, and there will be fried electronics after a while..If you want cheaper, 19 pins DB connectors, not the typical VGA, or it will be mis-used as well..

author: thm_w
author_rank: Super Contributor
timestamp: January 23, 2020, 12:52:14 am
content: Quote from: wraper on January 19, 2020, 10:23:48 pmMost cables do not have electronics, maybe one resistor, however, USB-PD emarked will have some ICs. So you might want to watch out what pins those are connected to. I believe if you stick with 5V or less Vcc it will be fine.Cables were discussed a lot in the RPL1116 thread.Finding fully wired passive cables was hard before, but now its getting a lot easier:https://www.primecables.ca/p-356977-cab-usbcm-cm-1ma-usb-c-31-to-usb-c-gen-2-mm-cable-with-aluminum-alloy-connector-primecables#sku365277These are a bit stiffer than typical cables.

author: tooki
author_rank: Super Contributor
timestamp: January 23, 2020, 06:15:57 am
content: Quote from: GeorgeOfTheJungle on January 22, 2020, 12:22:43 pmWill it really handle the ±25V allowed in RS-232 without damage? I kinda doubt it.Regardless, USB-C and USB 3.x are a huge clusterfuck. This has been discussed at length on the forum and elsewhere.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: January 23, 2020, 09:17:36 am
content: Quote from: tooki on January 23, 2020, 06:15:57 amRS-232? Hello? Tooki? It's 2020 already!

author: mansaxel
author_rank: Super Contributor
timestamp: January 23, 2020, 02:15:48 pm
content: Quote from: GeorgeOfTheJungle on January 23, 2020, 09:17:36 amI use it every day. Because it works.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: January 23, 2020, 02:37:30 pm
content: Quote from: mansaxel on January 23, 2020, 02:15:48 pmIn new designs? Bipolar? +/- 25V? Really? Thermionic valves work too but...

author: Berni
author_rank: Super Contributor
timestamp: January 23, 2020, 03:10:31 pm
content: Yeah you get at best +/- 10V out of your usual charge pump style RS232 transceiver IC these days. Even less for ones running from 3.3VAlso they have pretty limited current on the output so the ESD diodes in a USB port would probably just clamp it down.

author: Howardlong
author_rank: Super Contributor
timestamp: January 23, 2020, 04:56:51 pm
content: Quote from: Berni on January 22, 2020, 07:03:53 am..."using a cable"... and there's another rub! Not even apparently identical cables are the same, not by a long way. For a consumer it's a disaster.I'll also add my 2 cents that, both physically and electrically, USB Type C has shown itself to be very fragile. IMHO while the aim was noble, trying to share a tiny high density connector with high power and high speed data was a mistake. The USB receptacle itself has proven to be very likely to fail (as well as the high speed data muxes) and if soldered to a motherboard for example, it can be a very expensive failure, especially if the SSD is soldered in too.When it works it's great, my OH has an external 15" monitor that plugs into the USB C on her laptop, and all the power and video goes down the same cable. But not many USB Type C cables support high speed data/video and power delivery.Edit: when USB Type C works, it's often the exception rather than the rule.

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2020, 04:07:13 pm
content: Quote from: GeorgeOfTheJungle on January 23, 2020, 09:17:36 amWhen an external serial port is discussed without specifying a particular standard, it remains understood that RS-232 is meant. TTL serial is extremely rare for external ports. (The debug headers on PCBs don’t count as external.)RS-233 ports are still widely used in some applications, even if I haven’t used one in years. (And as a long-time Mac user, most of the serial I used back in the day was actually RS-422.)

author: frankb
author_rank: Newbie
timestamp: January 26, 2020, 12:31:35 pm
content: The first and most important consideration is whether you are talking about USB 2.0 or USB3.1.As has been said before in this thread- USB2.0 uses only 5V, GND, D+, D-, CC1 and CC2 (to communicate charge current).Since USB Type c connectors have so many connectors, it's conventional to use a 0.8mm PCB to fan out the leads, connect the CC resistors and other ICs if relevant, and provide solder points for the wires.Cautionary tale- making the PCBs for Type-C plugs is tricky (especially with Eagle as it's lightly allergic to milling slots)Secondly- 3.1 cables are short and often have active components inside.The standards are quite hard to get to grips with, and it seems the big players get it wrong (from my experience phones with USB Type-C 2.0 will draw more power than the communicated level by the supply.)Type-C does have some allocation for "other" uses like headphones (SBU1 and SBU2 I think).Regarding using it for "custom" pin allocation, perhaps it would be prudent to make a cable from plugs and clearly label things.Let us know what failures happen from interesting devices being plugged

author: NviGate
author_rank: Newbie
timestamp: February 07, 2020, 07:53:43 pm
content: USB Type C is just a connector type, which leads to much confusion. Although it works with USB 2, 3, 3.1 you have to really know your stuff.I use breakout boards from AliExpress for USB C mostly for power input and output, mainly because when I want to power a project, I always have a charger with a USB C cable handy.But you need to set the resistor correctly, if memory serves the resistor goes across CC1/2 to VCC. 56K Ohm limits to 500mA, 22K Ohm limits to 1.5A, and 10K Ohm limits to 3A.Be very sure your project and wires can handle that load.So, for general power input, it's great. For data transfer, not good unless you stick with D+ D- which are the only guarantee.For data, I thought about using HDMI Type C, not to be confused with USB C. It has 20 pairs I think. I know some vendors of PCI-E use HDMI cables to transfer.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 07, 2020, 08:22:23 pm
content: Quote from: NviGate on February 07, 2020, 07:53:43 pmAll compliant usb type c to c cables are required to support 3 amps and don't have any resistors, the resistors are provided by the device at the other end. Usb a to c cables are required to have the 56k resistor since all that is guaranteed to be available from a usb type a port is 500 mA. It still can negotiate higher using usb bc spec up to 1.5 amps on a dedicated charger port (i.e., shorted data pins). Many cables however are not compliant and have the wrong resistor in order to enable faster charging which can lead to failures when used with a usb A port that can't handle the load. Of course usb a ports are also supposed to have vbus short circuit/overcurrent protection but surprise, not all of them do.