Newsgroups: sci.electronics.misc
Subject: Re: How to get DC power from laptop port?
References: <[email protected]>
[email protected] (Jimbo156) writes:

> I have a laptop running Street Atlas 8, and using a GPS unit. It gives
> voice directions through the laptops' tiny speaker. It is not nearly
> loud enough and is hardly intelligble. So I plan to buy a little FM
> transmitter kit
> and connect the audio from the headphone jack to the input on the FM
> transmitter. Then I can tune the cars' FM radio to the proper freq,
> thus having a clear and loud voice for Street Atlas.  The transmitter
> runs on 6 volts DC. I would rather not have to bother with changing
> batteries, and don't want to have an additional power cord to tap into
> the 12V car power. The best solution would be to build it into a
> little box with either a parallel or serial port connector, and just
> plug it into the laptop. Problem is, is there any pin I can pick up
> suitable DC power from on either the parallel or serial port
> connector? Even 5 volts should be enough.

Thare are no specific "+5V out" pins on either PC parallel
pr serial port. You can "steal" some very limited power from
the signal wires (that's what serial mouse and paralle port
dongles do), but the available power is very limited.
More details on that can be found at:
http://www.epanorama.net/circuits/lptpower.html
http://www.epanorama.net/circuits/rspower.html

If you need any considerable amount of +5V (more than
few milliamperes), then roget serial or parallel port.
They will not supply the current you need.

Instead look for interfaces like PS/2 keyboard/mouse
port and USB ports. Both of those interfaces have
+5V available in them (at least 100 mA).
FOr more details read
http://www.epanorama.net/circuits/power_from_pc.html

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/