USB in python

[Grant Edwards]

On 2009-01-26, Lie Ryan <lie.1296 at gmail.com> wrote:

> How about (a crazy idea) using the audio jack out? (DISCLAIMER: Little 
> Hardware Experience). High pitched sound (or anything in sound-ology that 
> means high voltage) means the device is on and low pitched sound off.

 1) Pitch has nothing to do with voltage.  A high-pitch sound
    and a low pitch sound can have the exact same voltage.

 2) The OP's device requires quite a bit of power.  There is
    almost no power available from the line-out jack, and the
    voltage is limited to about 1V.  If his sound card has a
    power-amp (none do these days), he might be able to get a
    usable amount of power.

> The device will need an additional transistor to separate low
> voltage from the high voltage.

He'll need more than a transistor.  He needs a power supply,
some sort of rectifier/detector, and a comparitor. It would be
more interesting to use notch filters to detect different
frequencies so that you could have multiple output "bits".

> I don't know how much power can be pulled from jack out,

Almost none, and what's there is very low voltage.

> but for a home brewn device it is still feasible to draw power
> from USB and signal from jack out.

It would probably be easier to buy a USB-parallel port chip.
Then he's got power from the USB bus and something like 14
parallel I/O pins he can control.  Alternatively A USB-serial
chip will provide 2 outputs and 4 inputs.

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