USB in python

[Lie Ryan]

On Mon, 26 Jan 2009 11:08:48 -0600, Unknown wrote:

> 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".

>From the little I know on electronics, a simple, single transistor would 
(almost) immediately switch from on-to-off-to-on depending on the voltage 
of the control pin (I think it was the middle pin). I was suggesting this 
simplistic hack because as far as I comprehend the OP's need, he only 
need on-off switch instead of a complex 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.

That's why the power is taken from USB port.

>> 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.

The idea was made on the basis that a USB microcontroller is not used. 
Getting power from USB should be much easier than getting data while the 
jack out can provide simple on-off signal.