[AZ-Observing] Re: LapTop


Stan Gorodenski wrote:

>I am considering getting a laptop for my LXD75 to be able to use Meade's 
>LPI that came with the telescope, as well as possibly the DSI if I 
>decide to buy it at some time in the future. At one time I knew much 
>more about computers than I do now, and I have not kept up with changes 
>in technology. Can anyone recommend one that is relatively inexpensive? 
>Cost will be a factor on whether I will even get one. I would be using 
>Windows2000 as the OS. Some of the things I would like to know are
>  
>
I currently use a couple old (Dell Latitude Pentium 2, 300MHz) laptops 
for field use.  I have a modern high end HP that is my primary computer, 
but I rarely use it in the field.  The old Dell's are just fine, they 
don't chew much power, and I don't panic if they get a bit dusty or dew 
covered in the night.  (I had one time my mouse was frozen to the table! 
I had to pry it loose.)  The smaller hard drives (10Gb) are sufficient 
for CCD with a USB memory stick used to transfer the few hundred 
megabytes I can generate in a night.  The drives are a bit small for 
webcam imaging where the AVI's can get very large, very fast.  These 
machines were sold at an employee auction by my company as surplus, a 
lot of four for $20.  I got two working by stealing parts and memory 
from the others and buying a couple new hard drive and batteries.  
Surprisingly they run windows XP pretty well, one you shut off and 
de-install all the junk windows comes with.
 

>1. Are there differences in how they are powered? I remember years ago 
>laptops were pretty heavy because of the battery weights. Now they seem 
>pretty light. Are there less desireable batter power sources?
>  
>
Certainly look at battery lifetime as one criteria, but no laptop 
battery will get you through a whole night.  2-6 hours is normal, but 
heavy processing tasks (like webcamming) will cut into that.  I use an 
external 17Ah 12V battery pack that will run the camera and laptop all 
night.

The issue here is voltage, if you find a laptop that will run on 12V it 
is great, but I haven't seen any modern laptop that does.  18-20V is the 
usual input voltage, so if you use a standard 12V field battery you will 
need to boost the voltage. 

Avoid using a 120V converter and the standard laptop supply, these are 
horribly inefficient.  The 120V converters are usually less than 60% 
efficient, and the standard laptop supply is probably around 80% 
efficient, the remaining power is just wasted as heat from the 
conversion process.  Run through both and you are now throwing away half 
your power.

Look into buying a laptop travel charger, this will convert 12V straight 
to the 18V your computer needs at about 80% efficiency.

>2. What is a reasonable minimum processor to get? I know getting the 
>current most advanced technology processor is more on the safe side if I 
>plan on using the laptop many years, but it probably would be much more 
>expensive.
>  
>
The latest processor will certainly benefit you down the road, but you 
can save a lot of money by not going with the highest possible clock 
speed, staying just a couple steps back.  The only time you will really 
notice is when you are processing a stack of images, such as webcam 
imaging.  The other issue here is power, the higher end processors chew 
a LOT of power.  I don't generally use my big HP laptop (which I am 
typing on right now) in the field because it's 3+ GHz Pentium 4 is very 
power hungry. But on the other hand it chews through 1000 frame AVI's in 
Registax like butter.

>3. Any manufacturers to stay away from because of hardware problems?
>  
>
Stick with a mainline manufacturer, Dell, HP/Compaq, Sony, or similar.  
Quality is usually a little better, but the real determination is the 
availability of replacement parts, batteries, memory and such down the 
road. If you choose a very popular laptop the after market parts will be 
around for many years.  When I rebuilt those couple Dell Latitudes that 
were 6+ year old machines I could still get anything I needed very easily.

>4. What kinds of external ports should it have for a telescope?
>Stan
>  
>
At least four USB 2.0 ports, when you start connecting the telescope, 
webcam, camera, a mouse you will use these USB ports up quickly.   You 
can use an external USB hub to get more ports, but that is just more 
cable rats nest to setup/wrapup and it could need power as well.  An old 
fashioned serial port is nice as many things in astro still use standard 
serial, but USB/serial adapters a readily available and work well.  I 
run a Nexstar 11 through one with no problems at all.  Most laptops 
still have a traditional printer/parallel port standard.

Hope this helps!

Andrew

Andrew Cooper
----------------------------------------------------
http://www.siowl.com



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