Getting 5 volts from an Android tablet micro USB

On Sat, 1 Mar 2014 13:47:06 +0000 (UTC), Unbelievable wrote in comp.robotics.misc:

Hi Unbelievable

Android is an operating system. A USB port is hardware. Operating systems don't have hardware, at most they support it. So what are you talking about?

Could it be that the port is in fact a USB device and not a USB host? Try getting 5 volts out of the USB port of a keyboard or mouse or web cam. Or can those not be called real USB ports, either?

jue

news: snipped-for-privacy@4ax.com:

What is this - the Tower of Babel? Since when does a keyboard, mouse, or web cam have an Android operating system? I'm talking about an HP Slate7.

On Sun, 2 Mar 2014 06:27:46 +0000 (UTC), Unbelievable wrote in comp.robotics.misc:

Since when does having or not having an OS defines if the USB port is a host or a device?

What kind of connector does it have? If it is a female connector as you would typically find on e.g. computers then it is a USB host and should supply power for 5 loads, i.e. 500mA . If it is a male connector as you would typically find on keyboards, cameras, cell phones, external harddrives, memory sticks, .... then it is a USB device and will never supply power but consume the power coming from the host.

With a tablet it could in theory be either: is that port used to charge the tablet? Then you got a USB device connector because it must accept power coming into the tablet. Or is is used to connect other devices to it like e.g. external keyboard, mouse, ...? The you got a USB host connector because it must supply power to the other device.

jue

Does your Android device support host mode, and is your port in host mode? If so, you should be able to get +5 from it. If not, it's a USB device (and will not power the bus); it's still most certainly a USB port, just not a host port.

Joe Pfeiffer wrote in news: snipped-for-privacy@snowball.wb.pfeifferfamily.net:

Nope... It's not a real usb port if it doesn't have the ability to put out 5 volts. It's just a usb connection. False advertising. IEEE or some other regulatory committee should get together and make this terminology clear. USB means "Universal". If I can hook up a keyboard to it, it should work - but I can't because it isn't a real usb port. They shouldn't call it that if it isn't what they say it is.

Pin 4, on a real micro usb port, is supposed to tell the port what kind of device is hooked to it so it doesn't accept 5 volts while trying to put it out at the same time. And visa versa.

This sucks. Now I have to make another power supply just for one stinking chip...

The USB Implementers Forum has made the terminology crystal clear, and the standard distinguishes a "downstream facing port" (which seems to be the only thing you're willing to regard as a port) from an "upstream facing port"; it's in the standard.

Yes, Pin 4 tells whatever is connected to it what kind of port it is. That says nothing about being required to provide power if you're an upstream facing port.

Note that if your device doesn't support host mode your attempt to plug in a keyboard isn't going to work no matter how you power it.

On Sun, 2 Mar 2014 20:19:33 +0000 (UTC), Unbelievable wrote in comp.robotics.misc:

They did

and they did.

If you don't understand the commonly used terminology, then that's hardly their fault.

Really not "their" problem. If it isn't a USB host port, then it isn't a USB host port. Does it say anywhere this is a USB host port and not a USB device port?

Really not "their" problem.

jue