Below is a schematic of a full automatic NiMH battery charger circuit using positive integrated voltage regulator IC 7805 which is porviding a constant current to charge the batteries. LED in this NiMH charger circuit is working as a charging indicator so when the batteries become full
charged the LED will go off. The circuit can charge two NiMH rechargeable batteries at a time. The circuit has a four different current sources like 50mA, 100mA, 150mA and 200mA which is selectable with the switch S, so you can choose the suitable current source for your batteries for example if you want to charge 500mA NiMH rechargeable batteries you have to select 50mA current, for 1000mAh NiMH batteries select 100mA, for 1500mAh select 150mA and to charge 2000mAh batteries select 200mA.