A battery charger for NiCd, NiMH batteries can be done using electronic diagram below. This battery charger for NiCd, NiMH is made using traditional electronic components.
Since the maximum charge voltage measures 1.45 volts and higher trigger threshold is about 1.7 V, this voltage can be adjusted using potentiometer P1 to the value of 1.45 volts. TTL control signal output by the voltage divider R4/R5, constant current source built with transistor T1, which provides a current of about 48mA. If D1 illuminates, it means that the battery voltage is charged. If maximum load of 1.15 volts is reached, the Schmitt trigger swings, D1 turns off (charging is completed).
Since the lower trigger threshold is about 0.9 volts, every charging cycle must be started by pushing S1 switch . For 1.2v/1500mAh batteries which are charged with a current of 150mA, R1 must be 5.6 ohms, R2 = 12 ohms, T1 = 2N2904.