consumer and otherwise electronics questions

anto at anto at
Thu Aug 23 07:56:58 EST 2001

On Thu, Aug 23, 2001 at 12:01:14AM +1000, Damien Elmes wrote:

*cut descriptions of car MP3 player*

> * i'm going to need to power this laptop off the car battery. an

Car laptop supplies are available - they are generally pretty expensive
you can probably get one from IBM (assuming your laptop is IBM) I have
seem them at Harvey Normal as well.

> * i need a regulated 5V power supply for the LCD screen. what is the
>   line level of a laptop serial port? the alternative is regulating
>   the DC output from the car, but that's beyond my abilities. i'd need
>   to find schematics on the net somewhere.

While you *could* power the lcd from the serial port - the circuit would
probably be *much* more complicated than a simple low current 5v supply.
The main consideration is how much current your LCD is going to draw. Once
you know that it is relatively trivial to design a small power supply 
circuit. Or if you don't want to go to that much hassle you can buy car
power supplies relatively cheaply. (think of the walkman ciggerete lighter

> * i'm also on the look-out for a laptop battery for an IBM thinkpad.
>   is there a way to determine if the notebook is running off 'mains'?
>   this would allow my laptop to shut down properly when power is cut. 

Depending on your laptop the laptop it's self will know when it is on 
mains or not. I have gone a slightly different path with my in car mp3
player. The laptop can be set-up to suspend when the lid is closed, so
I disabled the lid switch & connected it's input to a relay switched by
the accessories circuit - this has the benefit of much faster startup's
and when I grab it out of the car the battery is always charged.

Hope I've helped.


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