USB power to external device

You "inform" the bus by properly enumerating your gizmo as a valid USB device.

-a

thanks, really helpful, any suggestions on a micro/usb widget that can do the enumeration?

martin

I cannot be much more helpful, but your device descriptor includes a "power required" field in milliamps. Any powered port (including the root hub in the pc) must be able to provide 500 ma. An unpowered hub port can only provide 100 ma. So you should be able to do what you want, but you will restrict the usb topology.

Regards, Steve

Here's a question. How about those USB enclosures or other USB devices that use a USB Y-cable? Presumably 1 device can only enumerate once, so it'll get 500mA on 1 cable, but the other cable will only get

100mA? Or also 500mA? I believe it's 500mA since most drives will need more that much(or even more) to work? How does it work then?

There are various micros from Cypress, Microchip, Silicon Labs, TI, Atmel, etc, which have USB device interfaces. Choose one. Choose a device class with which your device will conform (HID is probably simplest), and be sure to include the desired current draw in the device/configuration descriptor. Once the device enumerates, which means it's recognized by the operating system and the device driver is loaded, then you'll be able to use the 500 mA available to the port.

The point here is that you can't "steal" power from the bus ... you need to have a proper device connected to the bus before you are able to use all of the power.

-a

There's no such thing as a USB Y cable.

And before you jump my shit: I'm sure somebody's out there making them, but I wouldn't plug one into my computer or my device and expect anything to work (or not explode).

They're kinda like those USB turnaround thingies you see ... utterly pointless.

-a

Thanks for that, especially the last paragraph, something that hadn't crossed my mind.

martin

Found this, first hit on TI site, worth a read

martin

Have a look at:

100ma and 500ma, 5V, 3.3V, and USB RX and TX at TTL levels if you need them.

May be an overkill for what you want, may not be, but at least an alternative.

Don...

--
Don McKenzie
E-Mail Contact Page:               http://www.dontronics.com/e-mail.html

Crystal clear, super bright OLED LCD (128x128) for your microcontroller.
Simple serial RX/TX interface. Many memory sizes.
http://www.dontronics-shop.com/product.php?productid=16460

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thanks Don, and your KIT123 is still working :-) had a couple of vino's, so I read it in the am anyway, done some diging and found

might be something in it for you?

martin

Thanks for the good feed back Martin.

I'll have a good read of it shortly also.

I do have a couple of alternatives here as well:

15-Feb-2007 The FTDI VDIP1 module is an MCU to USB host controller development module for the VNC1L device. VDIP1 is supplied on a PCB designed to fit a 24-pin DIP socket and provides access to all UART, SPI and FIFO interface pins of the VNC1L device.

15-Feb-2007 The FTDI VNC1L USB Host Controller ICs not only handle the USB Host Interface, and data transfer functions but owing to the inbuilt 8/32-bit MCU and embedded Flash memory, VNC1L encapsulates the USB device classes as well. When interfacing to mass storage devices such as USB Flash drives, VNC1L also transparently handles the FAT file structure communicating via UART, SPI or parallel FIFO interfaces via a simple to implement command set.

Don...

--
Don McKenzie
E-Mail Contact Page:               http://www.dontronics.com/e-mail.html

Crystal clear, super bright OLED LCD (128x128) for your microcontroller.
Simple serial RX/TX interface. Many memory sizes.
http://www.dontronics-shop.com/product.php?productid=16460

No More Damn Spam: http://www.wizard-of-oz.com