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the usb has a fuse that resets it works in linux and windows
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the usb has a fuse that resets it works in linux and windows

by josheeg on Wed Nov 19, 2008 11:09 am

the usb has a fuse that resets it works in linux and windows or at least ubuntu debian linux.
windows gives you a notification popup.

So why bother put a fuse on the arduino usb?
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Re: the usb has a fuse that resets it works in linux and windows

by westfw on Wed Nov 19, 2008 11:53 am

The USB interface is SUPPOSED to have current limiting in the host (pc side), frequently implemented with the same sort of PTC fuse used on Diecimila and later Arudinos, and occasionally actively sensed and reported. However, some platforms apparently skimp on this, and there were reports in the Arduino forums of PCs resetting because an experimenter accidentally shorted out the power rails of his arduino. Aside from being annoying, there's a significant safety factor involved; a PC power supply without some sort of limiter can provide several 10s of amps on the 5V rail; plenty to turn ordinary wires and other components into "igniters." An extra fuse doesn't hurt anything...
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Re: the usb has a fuse that resets it works in linux and windows

by josheeg on Wed Nov 19, 2008 12:24 pm

westfw wrote:The USB interface is SUPPOSED to have current limiting in the host (pc side), frequently implemented with the same sort of PTC fuse used on Diecimila and later Arudinos, and occasionally actively sensed and reported. However, some platforms apparently skimp on this, and there were reports in the Arduino forums of PCs resetting because an experimenter accidentally shorted out the power rails of his arduino. Aside from being annoying, there's a significant safety factor involved; a PC power supply without some sort of limiter can provide several 10s of amps on the 5V rail; plenty to turn ordinary wires and other components into "igniters." An extra fuse doesn't hurt anything...


Yes a pc power supply can provide that much but the usb port can not. .5 amp max I think is the standard...
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Re: the usb has a fuse that resets it works in linux and windows

by fe2o3fish on Wed Nov 19, 2008 3:36 pm

josheeg wrote:Yes a pc power supply can provide that much but the usb port can not. .5 amp max I think is the standard...


500-milliamps (0.5-amps) is the most a USB slave device can request. If the USB controller chip
in the slave doesn't do this request of the USB Master (or there is no controller in the slave device)
then the most the USB port is supposed to supply is 100-milliamps, or 0.1-amp.

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Re: the usb has a fuse that resets it works in linux and windows

by josheeg on Wed Nov 19, 2008 4:39 pm

Fe2o3Fish wrote:
josheeg wrote:Yes a pc power supply can provide that much but the usb port can not. .5 amp max I think is the standard...


500-milliamps (0.5-amps) is the most a USB slave device can request. If the USB controller chip
in the slave doesn't do this request of the USB Master (or there is no controller in the slave device)
then the most the USB port is supposed to supply is 100-milliamps, or 0.1-amp.


so I guess thats why I wonder if the fuse is nessisary if you didn't hack the usb port or got one that is falty. But I guess a counter argument is that much might still hurt someone or something...
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Re: the usb has a fuse that resets it works in linux and windows

by fe2o3fish on Thu Nov 20, 2008 1:16 pm

josheeg wrote:so I guess thats why I wonder if the fuse is nessisary if you didn't hack the usb port or got one that is falty. But I guess a counter argument is that much might still hurt someone or something...

It's a little like chicken soup -- it couldn't hoit! :)

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Re: the usb has a fuse that resets it works in linux and windows

by westfw on Thu Nov 20, 2008 7:34 pm

Yes a pc power supply can provide that much but the usb port can not. .5 amp max I think is the standard...

yes, 0.5A is suppsoed to be the max. But some PC manufacturers were apparently too cheap to include any limiting, just connecting the USB power pins to the main power rails.
(or, put another way, it is also "standard" that a USB peripheral must not draw more than 0.5A, and the fuse on the arduino ensures that this is true, even in the presence of user mistakes.)
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