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USB cables, connectors and protocols


  • Universal Serial Bus (USB) is an industry standard 1st introduced in 1996, for hot-swappable (do not need to reboot the computer to plug in) power supply and data communication which replaced the previously ubiquitous RS serial ports and cables. Microsoft Windows 95, OSR 2.1 provided OEM support for the devices in August 1997.
  • unfortunately with the variety of connector types and protocols now available it has become a major source of frustration, particularly when you also start to add in Apple Lightning and Thunderbolt connectors (Thunderbolt 3 uses the USB-C connector) and similar.
  • European Union has announced in 2021 it will ban devices being sold which are not USB-C compliant within the next 2 years or so in an attempt to unify the situation, reduce confusion and waste. Hopefully the rest of the world will follow suit.
  • USB cable not working?
    • if charging from a computer does the USB port you connected to have power out?
      • not all USB-A ports have power out!
    • if charging from an AC charger - does the charger output sufficient power?
      • old 5W iPhone chargers will not charge an iPAD - you need at least 10W charger for this
    • some USB-A type cables will be data only, some will be power only, and some will provide both
      • you can get a cheap small device that can check your cable type as this is a key area of frustration when connectors fit but the device doesn't work due to using a cable for another device
    • cable may be broken
      • you can buy a RJ45, RJ11 and USB cable tester, or,
      • musicians have XLR/audio/midi/USB-A cable testing devices
    • consider buying a USB in-line power meter if charging seems to be the issue
      • this will show if a device is being charged or not, and how much charge is being sent
  • be careful running USB car cigarette lighter adapters in your car - some cause a lot of RFI even without devices plugged in to them!
    • these devices convert 12V DC to AC then to 5V DC USB out and in the process some may generate radio frequency interference (RFI) typically at around 2m wavelength amateur radio with 15-30Db noise which may also create issues for your car's RF controls such as keyless entry, tire pressure sensor systems, air bag systems, etc as well as your CB radio and perhaps your AM/FM radio.
    • buy good quality devices and don't overload their rating
    • note that car cigarette lighters themselves generally are rated at 12V 10A max = 120W

Connector types

  • by design, it is difficult to insert a USB plug into its receptacle incorrectly
  • some computer USB ports supply power to power USB devices.
    • most of these supply power at 5V ± 5% and devices may draw loads as follow:
      • low power device: 100mA/0.5W (USB3 150mA/0.75W)
      • high power device: 500mA/2.5W (USB3 900mA/4.5W)
      • battery charging devices: 1.5A/7.5W (v1.2: 5A/25W)
      • Power Delivery (PD) 20V port: 3A/60W micro-USB (5A/100W USB Type A/B or USB-C 2.0/3.0)
      • Power Delivery (PD) 48V port: 5A/240W USB-C 3.1
  • USB-A
    • this is the standard, original PC connector and it has a large white connector with 4 pins (1 power, 2 central data pins, 1 ground)
    • it is designed for USB 1.x and USB 2.x protocols with speeds up to 480Mbits/sec
  • USB-A super speed USB 3.x
    • this is same physical size as USB-A but has a blue connector instead of white, 5 additional pins, and supports USB 3.x as well as older USB protocols, and when connected to a USB 3.x device allows data at up to 10GBits/sec
  • USB-B
    • these are square versions of the USB-A including a super speed version with a second input for the extra 5 pins
  • USB-C
    • these are small, flat connectors with 24 pins and compatible with USB 2.x and USB 3.x to give speeds up to 20Gbits/sec and also compatible with USB 4.x developed in 2019 (Thunderbolt 3 and 4) which allows up to 40Gbits/sec
    • this connector should supercede most other if not all USB connectors and unlike previous connectors the cable is reversible
  • USB mini connectors for the device end
    • these are 6.8mm wide and come in 3 main types for USB2.x (each with 5 wires):
      • Mini A
      • Mini B
      • Mini AB
  • USB micro connectors for the device end
    • these are 6.8mm wide and come in 3 main types for USB2.x (each with 5 wires) and each have wider superspeed USB 3.x versions with 10 wires:
      • Micro A
      • Micro B
      • Micro AB

USB protocol

  • USB device communication is based on pipes (logical channels) which are connections between the host and the logical connection in a device - each USB device can have up to 32 endpoints (16 in and 16 out), though it is rare to have so many.
  • The functionality of a USB device is defined by a class code sent to a USB host eg. audio, printer, etc
photo/usb.txt · Last modified: 2021/10/10 21:07 by gary1

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