buttonremoterepair
On almost every remote controller the buttons stop reacting after a while, and you end up squeezing the remote out of his life while trying to switch the channel…
I found some link where it explains how to "refresh" the contact-making surface on the backside of the buttons, but that kit is not something I can find around. Could you suggest what would be a good replacement?
Try checking out http://www.diydrones.com/ it may answer a lot of your questions.
As for multi-km links RF waves travel at the speed of light which is 299,792,458 meters per second that's more than fast enough for realtime control. The problem with long distance links is that for a frequency high enough to support realtime high-quality video such as microwave frequencies are line of sight for the most part.
In order to get past free space attenuation you'll also need some power over FCC legal limits I'd assume, but you can get past that by getting an amateur radio license. There are ways around this, directional antennas but thats a whole story by itself. (I am not a lawyer, I am however an Amateur Radio Operator)
Free space attenuation of signals (path loss) can be calculated as follows: Lfs = 32.45 + 20 log d + 20 log f
Where
Lfs = Free space loss in dB
d = distance in km
f = frequency in Mhz
Hope this helps!
First, a lot of microcontrollers and digital signal controllers will have internal pull up resistors. Here's an example, an Atmel ATMega164. 
There will typically be a register that allows the internal pull ups to be turned on and off. Due to variations in the fabrication process, these internal pullups come in a very wide range, and are not a good choice if you need very close control over current draw in ultra low power applications. If keeping component count low is important, this is an easy way to do it. Using internal pull ups for hardware debounce would not be a good idea, since it's not possible to predict their exact value.
Whether the 100\$k\Omega\$ value is adequate depends. If it's just a switch that will be periodically flipped by a user, then 100\$k\Omega\$ would be a good choice for minimizing power consumption. For things that are going to switch more rapidly, such as rotary encoders, the process I would go through is
So if the maximum sink current per GPIO pin were 10 mA and operating at 5V: \$R=\dfrac{V}{I}=\dfrac{5V}{10mA}=500\Omega\$. Keeping this R value small as possible will allow for the sharpest edges and highest switching frequencies.
Best Answer
I've used aluminum foil with great success before. You can get it from a gum wrapper like Nick T suggested. Just make sure you don't use super glue, it'll dry out the rubber in the buttons and cause even more problems.