[sdiy] semi-OT: USB cable shield

[MTG]

AFAIK ground and shield are different things as far as a peripheral are 
concerned. On the PC host they are probably joined but my understanding 
is that the shield extends from the PC via the shielded cable to 
whatever part of the peripheral is shielded. Thus you can send all the 
garbage back to the PC but not necessarily through the ground wire.  Maybe?

GB

On 4/22/2014 12:19 PM, Colin f wrote:
> At a guess, assuming the outer shield makes contact first, the high
> resistance would limit the sudden current flow between ground isolated
> devices that might be floating at very different DC voltages.
> Once the ground pin connects, you get the low resitance connection you need.
>
> Cheers,
> Colin f
>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Ingo Debus
>> Sent: 22 April 2014 20:13
>> To: synthdiy diy
>> Subject: [sdiy] semi-OT: USB cable shield
>>
>> Hi all,
>>
>> as far as I know, the shield of USB connectors usually is
>> connected directly to ground. However I've seen designs where
>> there's a smallish capacitor (10 nF) in parallel with an 1
>> megohm resistor between the housing of the USB receptacle and
>> ground. Why is this? I understand this is done for MIDI
>> connectors to break up ground loops (see? it's not completely
>> OT), same for Ethernet, but USB? USB connectors have a ground
>> pin anyway, so it seems pointless to me to break the ground
>> shield connection for low frequencies while there's still a
>> direct ground connection via the pin.
>>
>> Any Ideas?
>>
>> Ingo
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