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Frolinmod / Rally
The reason I'm after a hub that can “smoothly (electronically)” turn of a port is the dreaded “Blue screen of Death” (BSD). If you google “usb blue screen of death” you will see this problem going back decades and usually the problem relates to drivers/software updates etc. Most of the time they are right but I'm almost certain there is another hidden problem that relates to what happens when an electronic device is plugged into a usb port causing the crash. Take for example a when a web camera is plugged in. All the bypass capacitors on board the camera start to charge from 0volts to 5volts and even though the camera may use 90 milliamps in normal operation the charging current surge is 1-3 amps for up to 10-20milliseconds. At the same time as this is occurring the power contacts in the plug are making and breaking as the plug is seated, causing the charging current surge to break up into a series of short high current spikes. These feed into the hub and onto the pc and I suspect randomly cause the BSD by either a current overload or some kind of ground current spike the pc doesn't like. In my case there is also about 4 metres of usb cable with associated inductance that will cause ringing and possible negative voltages to be produced which is something you really don't want around digital circuits. For the moment what I have done (and have yet to test) is to take a usb isolator (see attached file) and remove the +5v/+5v isolated supply stopping the pc from supplying power to the hub and to force the isolator to use only the +12v at the mount. This is connected between the hub and the pc so the ground and power lines from the pc are totally isolated. This should prove one way or another if I'm right about these current surges causing the crashing. The other option was to use a clever hub that would turn on/off a port smoothly with a transistor of some kind thereby avoiding current surges. But that may be asking too much from manufacturers.
Marc (multiweb) Don't worry about the cables. If the heat-sinks were that hot you pcb would probably be on fire anyway. Well maybe not on fire but they wont get that hot as the dew output is pulsed – hard on – hard off so it's reasonably efficient.
Cheers
Stephen
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