Let's Make Robots!

converter

AD & DA converters - at a total loss.

I'm doing some non-robot project to learn more electronics. And boy have I got a lot to learn!
Right now I'm trying to take an analog signal, convert it into 8bit digital info through an AD converter, and then back to analog using a DA converter.

9v battery in a picaxe

hi

i plan to install a micro spy-cam inside my quadropod(SC-QR-1)

ive allready got the cam and it uses a 9volt battery to power it!

a problem is that the 4 AA batteries inside takes all the extra space inside, but if i took another 9volt battery with some kind of converter that makes 9 into 6 volt to power my robot!

the question now is: 

what should i use?

 please tell me what, where to buy, and the price of it! =D

EDIT: do you think something from these sites might be usefull?:

Steps battery voltage up or down.
The MC34063A is an easy to use DC-DC converter that can be used to step battery voltage up or down to run your processor, small servos or to make an efficient LED … Read more