Astan Chee schrieb:
Diez B. Roggisch wrote:
Others suggested the parallel port. It is the natural choice for such
things, with two caveats:
- it is legacy, and thus often not available on modern hardware,
especially on mobile ones. So if you want it be prepared to
additionally buy a usb2parallel-adapter.
- it's electrical specs aren't as robust I fear. USB allos up to
500mA to be drawn, and shouldn't break if you try more & fail (albeit,
that might be something that isn't true all the time). So you can draw
quite a bit of current from it (the stupid USB-cup-warmers are an
example of that). I have often had broken parallel-ports, and I think
the reason is that they *ARE NOT* specified to drive anything - they
only provide low-current control-lines. So whatever you design, you
need a second power-source then.
All in all, using a USB-controller is IMHO the best solution. The
AT90USBKey is a low-cost evaluation-board. ATMEL provides quite a bit
of example-code, and there is other FOSS available.
I have to admit though that the whole USB-topic isn't the easiest thing.
Yeah, I forgot to mention that the device is requires about 70-80mA and
the parallel port (according to the spec) only provides 1mA. Thats why I
was looking into the USB solution.
Thanks for the suggestion though. Also, yes, the device is rather mobile
and that is why it is powered by the computer/laptop but legacy isn't
really an issue for me I guess.
If all you need is on-off - why can't you just use a switch?
Diez
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