The USB interface is one of the most popular interfaces to connect
secondary equipments to the host. The USB interface itself is standard,
but you may face the problem of connecting every device to a USB enabled
computer because of the lack of right cable. This happens because for
smaller equipments like cameras, there are different models of USB
connectors.
Basic design of USB connectors
Much effort has been put to design different USB connectors for
different purposes. The old Centronics connectors for parallel printers
were huge and needed clips to connect them safely to the devices. The
DB9 and DB25 connectors used for RS232 ports and parallel ports on
computers had problems with connection bolts falling out of the computer
case when the screws of the connector were tightened. Moreover, people
felt that the pins of these connectors bend easily.
Another disadvantage with the bad connector design is that you may
sometimes connect them wrong. This happens mainly with flat cable
connectors and power connectors inside computers.
The Standard A and B USB connectors
Because of all these drawbacks, two USB connectors are defined for
basic use, the USB A connector which must be used on devices that
provide power mainly on computers and the USB B connector are used on
devices which receive power like most of the peripheral devices.
There are four pins that are defined in the standard USB A and B
connectors in the USB 1.1 and USB 2.0 specifications. Two of the pins
are used for power and the rest two pins are used for differential data
transmission. The pins for power connection are slightly longer in order
to first connect the power supply when connecting a USB device. This
reduces the chances of receiving dangerous voltages.
Mini USB A and B connectors
The standard A and B USB connectors are perfectly suited for devices
like modems, printers and scanners. But with launch of the faster USB
2.0 specification, the USB not only connected huge and slow equipments
but also smaller and faster devices like mobile telephones, photo
camera. The standard USB B connector was too big to fit on smaller
equipment like these.
A smaller version of the B connector was released with the name Mini-B
connector. The main difference between the standard USB A and B
connectors with the mini USB A and B versions is the extra pin called
ID.
Micro USB AB and B connectors
With time, the mini USB B connector soon became too large for new
equipment like cell phones. That is why, in January 2007 came the micro
USB connector, which could be easily connected to thinner devices than
the mini USB version. The micro USB is much thinner than the mini USB
connector and has been especially designed for rough use. This micro USB
connector is specified for at least 10000 connect/disconnect cycles. The
only difference between the micro USB connectors and the mini USB
connectors is that the ID pin in the micro USB AB connector has now a
function to play.
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