Circuit Project Electronic

The charger consists of two stages: The first is a capacitive voltage doubler, which uses a 555 timer IC driving a pair of transistors
connected as emitter followers, which in turn drive the voltage doubler proper. The doubler has power resistors built in, which limit the charging current.
The second stage is a voltage regulator, using a [...]

In this circuit, the 7815 regulatates the positive supply, and the 7915 regulates the negative supply. The transformer should have a primary rating of 240/220 volts for europe, or 120 volts for North America. The centre tapped secondary coil should be rated about 18 volts at 1 amp or higher, allowing for losses in the [...]

Introduction
With this mAh meter you can check the mAh capacitance of your NiCad or NiMH rechargeable batteries
Normally the cheaper NiCad AA-type cells have a capacitance of 500-750mAh (NiCAD) the more expensive
NiMH AA-cells types are up to 1800mAh.
I built this circuit because the capacitance of some of my older NiCad batteries seemed to be quite [...]