usb power? (macintosh)

Archiver

Hi all,

Does anyone know if it's possible to use the power from a usb port on
a macintosh (using a keyspan serial adapter for the stamp) to power a
basic stamp device?

Just wondering.

Matt

Archiver

--- In basicstamps@yahoogroups.com, "lmig_bj" <gilb_jm@y...> wrote:
> Hi all,
>
> Does anyone know if it's possible to use the power from a usb port
on
> a macintosh (using a keyspan serial adapter for the stamp) to power
a
> basic stamp device?
>
> Just wondering.
>
> Matt


The spec for the USB is on the order of 500mA. Check your project
and see what the max will be.

I would measure the voltage CLOSELY and keep adding a load until
there was a voltage drop of about a half volt. Whatever that load is
would be about the edge of the cliff load.

I am not well versed in USB, but the specs on the parallel port call
of a load and voltage. is: 2.5 volts at a 2.5 mA load.

That means to meet the spec, you could start with 12 volts, just so
long as there is still 2.5 volts when there is a 2.5mA load.

What that means to you is that the voltage MAY NOT be 5.0000 volts,
but may be 6 or 7 or something.

Hope that is a starting point.

But, I think some testing of the available current is in order.

Dave