I was reading up on USB connectors on Wikipedia and I've noticed that the contacts for the data lines (D+ and D-) are shorter in both the Type A and Type B plug.
What could be the reasoning behind this design?
Electronic – Why are the contacts for the Data lines in USB A and B plugs shorter than the contacts for Ground and Power
connectorusb
Related Solutions
If I am not getting confused, this system of resistors is required by iPhones and other i-Devices to charge at different current levels. Otherwise an error message will pop up. If you don't have an iPhone you can quite safely remove these and replace them.
Apple stopped being as 'lax' with the charging interface and started being very picky about having the official chargers. We still doubted that there was an enumeration chip inside each charger - too expensive and complex. So there must be something else going on in those data lines. Time to sacrifice an official Apple iPhone 3Gs charger!
Taking it apart, desoldering the 4 data line resistors and measuring them on our multimeter, we found the following as shown in the schematic:
Put a disconnect switch in the power line, but leave the ground connected all the time. This works fine and does what you expect.
(Obviously if you try this with a self-powered USB hub or device it may ignore you turning the power off, but most are bus-powered devices.)
Best Answer
Hot plugging. You want the power supply to be connected before the datalines. Some chips may latch if a signal is supplied to the signal pins before power is applied. This means the chip will internally short out and may get destroyed when subsequently power is applied.
In the old days you had to power off you computer before you could add a peripheral to it, that is not necessary with USB (and some other interfaces).