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USB Condom (take 2)

Tried to post this through Teranews.com and it seems to have gotten stuck somewhere. Trying again now through eternal-september.

I recently saw an advertisement for a USB Condom that, essentially breaks the data path between a computer used for charging and the peripheral device. I tried making one of these with a chopped off Type A connector from a A/B cable. Colors I got (looking into mating face with logo side up) of the USB Type A cable connector were as follows: Pin 4 Blk common (to left side) Pin 3 Grn D- Pin 2 Wht D+ Pin1 Red Vbus (5v) (to right side)

Used a Molex 87520-0010BLF PWB through-hole type A connector as my socket. Connecting 1:1 confirms that this does work as an extension cable.

Using my 5th generation iPod/touch (with lightning cable) as a test, just connecting the Vbus and common weren't enough to cause a charge condition. By trial and error, found that connecting on receptacle (peripheral) side, a

10K from Vbus to D+ and leaving the data lines otherwise disconnected would cause the iPod to charge.

iOS7, by the way now warns when you plug into a computer, "do you trust this computer?" as data theft from plugging into charging kiosks has become increasingly a threat.

Oppie

Reply to
Oppie
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Came through here, oddly (also ES).

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

Take2 was sent through ES and showed up on Teranews almost immediately. Original post is stuck in tera's input filter somewhere. Also tried responding to several posts through tera. Some propagated and others didn't.

Thanks for the heads-up.

Reply to
Oppie

There is some standard for a USB port to recognize that it is charging a battery, with a protocol to make it happen.

That's about all I know, and it's deduced from reading the features list of the FTDI FT230.

Presumably any proper USB condom needs to be thin enough that the USB plug can sense the computer's desire to give a charge, yet impenetrable enough that it neither allows its DNA out, or receives undesirable DNA from the receptacle.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

That sound about right, My Motorola V Rzr has the pullup on its charger plug (mini usb)

Cheers

Reply to
Martin Riddle

On a sunny day (Fri, 4 Oct 2013 15:22:33 -0400) it happened "Oppie" wrote in :

Yes, made one like that some year ago, so I could charge little 2 inch Chinese video player... Else it would go into data mode all the time on the PC... Just tested out the USB signal wires, do not remember what resistor I used. Cannot find the circuit diagram either, had it in my hand yesterday. Did I connect BOTH signal wires together?

Reply to
Jan Panteltje

Yes, disconnect the D+ and D- wires at the the power source end of the cabl e and link them together at the client end. Its all in the USB standard wh ich is downloadable free.

If you use such a cable to get power from a PC, it may only deliver 100mA, depending on how strictly the PC interprets the USB standard. If it is con nected to a suitable 5V power supply, then much higher currents are availab le.

Old USB devices from the days when there was no standard for "dumb charging " look for a combination of pullup and pulldown resistors on D+ and D-. Ap ple used a different configuration from nearly everybody else. Yet another non-standard method used a long time ago by Motorola was to have a link be tween D+ and D- and a resistor to ground connected to the sense pin of a mi ni-USB the value of which controlled charging and backlight status.

John

Reply to
jrwalliker

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