[Cialug] Pressing a button remotely

[Matthew Nuzum]

On Wed, Jan 28, 2009 at 4:16 PM, Zachary Kotlarek <zach at kotlarek.com> wrote:
>
> On Jan 28, 2009, at 3:20 PM, Nathan C. Smith wrote:
>
>> Yes doing it yourself is part of the fun.  And Parallel printer ports are
>> harder to find these days (no, I don't want your old Pentium)
>
> Your serial port, or your USB->serial port, has some current available on
> the flow control pins. It's not a lot of power -- a typical max is 50ma per
> pin -- but since you're only looking to drive a solid-state,
> low-output-current relay it should be sufficient (if you size the components
> correctly). And you could hijack the USB line for more power if you're using
> a USB->serial adapter and were willing to build a slightly more complicated
> circuit.
>

If you have a usb to serial adapter you can have up to 500ma from the
5v line of your USB port. Well, 500ma including the draw of the serial
port. That's enough for a diode and a relay.

FTDI makes a very hacker friendly usb part. http://www.dlpdesign.com/
has some details, especially the 232R. It has windows, mac and Linux
drivers and in addition to being a usb to serial adapter it also has a
"bit bang" mode that lets you do things like toggle a relay.

However a more fun and exotic solution that doesn't require a computer
would be to write a little java app that runs on the boost mobile
phones. They have a serial port so you could write an app so that you
can just send it an sms and trigger the door open or shut. Or you
could pay the $0.35 per day for internet access and trigger it via the
web :-)

-- 
Matthew Nuzum
newz2000 on freenode, skype, linkedin, identi.ca and twitter