0 Ni-Cd charger (no transistor and IC)

Perhaps the simplest Ni-Cd charger available in the market. R1 and the LED will indicate the charging state while R2 controls the charging current. You can charge any number of cells in series by changing the values of R2 and keeping the voltage difference between the DC in to Bat around 3V (minimum).

Ni-Cd charger schematic

Part List :
R1 - 100 ohms 1/4W
R2 - see notes below
LED - red  or any low power LED (3mm or 5mm)
DC in - must be 3V higher than the battery voltage (see notes below)

Adaptor ( DC in )

Notes :
The charging current is limited around 25% of battery rating and given by the simple equations:
Current = 0.25*(mAH rating) ; so the charging will be 4 hours for fully discharged battery
R2 = (DCin -Bat) / Current
Example: 1.2V battery rated 1200mAH , DC in = 4.5V
Current = 0.25 (1200mAH) = 300mA or 0.3A
R2 = (4.5 - 1.2) / 0.3 = 11 ohms or just use 10 ohms (1W)  just use 5W rating to make it very safe

Other Ni-Cd charger :
USB Ni-Cd charger - charging your battey through usb port of your PC
Simple Ni-Cd charger - simple and automatic charger

Other useful charger :
iPhone Charger circuit -idea of iPhone charger
Universal charger - charge any battery voltage form 1.2V up to 12v
Mobile phone charger - very simple charger for phones