Here is a nice article wrote by LBMiller5 a member on RCGroups.com forum.In this tutorial he talk about how to build a 6-cell pack battery pack from A123 Cells that he buy from eBay.The 6-cell pack built here has a open circuit voltage of 6 x 3.6 volts per cell for a total pack voltage of 21.6 volts, and has a capacity of 2300mah. The pack can deliver 30C continuous (69 Amps) with burst capability of 40C (92 Amps). source
This is a nice article about How to Making Excellent Printed Circuit Boards without dry film photoresist.Stefan writes:
This article was originally written as a letter to some of my friends who wanted to know why my printed circuit boards turned out so well. After I sent it, they suggested I turn it into an article. So, here it is:There are only a few secrets to making really good printed circuit boards. The first is to get everything completely clean. The second is to use a good etch resist.
Some we need a negative resistor in the circuit we can take advantage from Field effect transistors(FET).source
The basic idea is to group the 7 pins that are needed to drive the LCD in only 3 using a shift register. This is a cheap alternative to serial LCDs. The schematic shows that wiring the LCD is a simple operation. It has been drawn in a way that makes possible to develop this as part of a single sided PCB including a variable resistor to control the LCDs contrast.source