USB Merge

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ouroborus
 
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USB Merge

Post by ouroborus »

The schematic is of a cable intended such that power is from from one source and data from another. The merge side would be attached to a usb device. The data side would be attached to a laptop. The power side would be attached to a usb charger wall wart. Is this sort of thing feasible? Am I doing it right? Does such a thing already exist?
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zener
 
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Re: USB Merge

Post by zener »

My concern is that your power be properly regulated. A charger or wall wart may not be.

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dr. au-fait
 
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Re: USB Merge

Post by dr. au-fait »

That should work fine as long as the grounds are at the same potential or one is floating. Most USB ports are fused, but a shift in ground potential can fry something on your PC/laptop main board. I learned that lesson with a USB oscilloscope.

The regulation of the voltage from your secondary source is important for signal quality. Most wall warts are pretty good regulators if they're spec'd for 5V since the typical application for that voltage requires tight regulation.

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zener
 
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Re: USB Merge

Post by zener »

Historically, DC wall warts are unregulated. Only the newer switcher type are typically regulated. The older kind can float very high. Check with a meter before you hook it up.

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ouroborus
 
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Re: USB Merge

Post by ouroborus »

I was thinking of those wall warts specifically marketed for USB charging. Like http://www.cobyusa.com/?p=prod&prod_num ... at_id=4002

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