Monday, September 8, 2008

Tablet Ubuntu 8.04 Howto

http://timelady.com/blog/howtos-technical-guidestips/kubuntu-804-hp-tc1100-tablet-functions-howto/

Ubuntu on TC1100

http://wiki.linuxquestions.org/wiki/Tc1100

Led Calculator!

http://ledcalc.com/

Hooking up led's to a case... more on this in the future!



































Circuitry
101: How to Hook Up LEDs









The
direct url for this guide is: http://tutorial.lsdiodes.com







Below we've created
a

very

basic guide to help people unfamiliar with circuits
get their LEDs up and running without blowing them out and wasting
all
their money. IT IS VERY BASIC!! Current is hardly ever mentioned, not
because it's not important, but because we've found it makes things
confusing when trying to teach people about this sort of thing. If
we've
done a bad job explaining things or if you have a question this
doesn't
answer, use the contact form at the bottom of this page to let us
know
what's up.





There's two basic
types of circuits:


Series


and



Parallel.









Series







or "How do
I power lots of LEDs off a higher voltage source?"






When
LEDs are placed in a series, the voltage is dispersed between the
LEDs,
meaning less voltage goes to each LED. This can be very useful. For
example, if a 12 volt adapter were powering one LED, there'd be 12V
going through that LED which is way too much for any LED to handle
and
would result in a rather unpleasant burning smell.





However, if you
take that same 12V power source and put 4 LEDs in series, there would
be 3V going to each LED and (assuming the LEDs are made to run off
3V)
each would be powered and just dandy. Check out this illustration:




LEDs wired in series





It's important to
notice how the LEDs are positioned: (-) (+), (-) (+), etc. making
sure
that the end (-) connects to the (-) wire and the end (+) connects to
the (+) wire, if any LEDs are backwards nothing bad will happen, they
just won't turn on.





If three LEDs were
in series with a 12V source, each would receive 4V, if six were in
series,
each would receive 2V, etc.






"But
what if I have four LEDs powered from a 12V source and I want each to
receive less than than 3V/ea?"

This is where the little
'Resistor(s)' squiggly comes in. By adding a resistor it's possible
to tone down the amount of voltage each receives. To find out what
value
resistor you should use, use an led calculator such as

this one

. Go to the middle form where it says 'LEDs in series' and simply
type in your power sources' voltage, the LEDs' voltage you'd like and
the LEDs current capability (use 20mA.) It then tells you what ohmage
resistor to stick in the circuit.







Parallel




or "How d



o
I power lots of LEDs off a lower voltage source?"






Let's
say you wanted to power three of your brand new LEDs off a 3V battery
pack (two 1.5V AA's in series, make sense?) you found lying around.
If you were to series the three LEDs there'd be 1V going to each (3
Volts / 3 LEDs = 1V for each LED). That's not enough to power your
LEDs!
You want them to have the full 3V going to each. Here's how:




LEDs wired in parallel





How this works is
that while every LED receives the same amount of voltage, the current
of the source is dispersed between the LEDs. What this means for you
is that you have 20 LEDs paralleled off a battery, it's going to
drain
the battery a lot quicker than if you only had 2 LEDs in parallel. If
you're paralleling off a wall adapter, for instance though, the
source
can constantly renew itself so you can essentially parallel as many
as you'd like without fear of draining the wall ;P.




To use resistors
in a parallel circuit, say if you'd like each LED above to receive 2.5V
instead of 3V, use an
LED calculator
(make sure you're in the parallel section) to find
the right ohmage and then stick it somewhere in the circuit!






"Why
do the LEDs have to be the same color?"

If you mix colors,
say if you paralleled a red (~2.3V) and two blue (~3.5V), the blue
LEDs
would not light. Why's this? Because the electricity is going to take
the easiest path it can to complete the circuit and in this scenario
the red LED requires less energy, leaving the two blue unpowered and
lonely. To fix this you would need to stick a resistor onto the leg
of each LED to 'equalize' all of the LEDs. Note illustration:




Different colored LEDs wired in parallel




To find the resistor
you'd need for each LED, use the 'Single LED' portion of an
LED calculator
, type in the supply voltage, LED's voltage and 20mA
for each LED and there you go. Now each LED will turn on and each will
receive it's desired amount of power. Thanks to Mike Moorrees for pointing
this out, "The resistors act like 'shocks' in a car, they give the
power source some 'squish' and let each LED find its happy place (forward
voltage)."


LED
calculator thanks to Japala: http://www.metku.net

Friday, September 5, 2008

Dell PA-12 Power brick quick repair

Fixing the Dell PA-12 from eternal doom... The plug is not as good as they used to make it :)

Take it apart, put it back together!