Using this electronic circuit diagram can be designed a very simple charging circuit for NiCd batteries. This electronic charger allows simultaneous charge of four NiCd batteries of 9 V , cursor of P1potentiometer set voltage that will used for recharge of batteries.
Cursor potential is also applied to the noninverting inputs of four comparators, IC2a - IC2d, using 100 k resistors. When the battery voltage is too low, the comparator associated switch, causing transistor for conducting, so the battery is charging.
Charge voltage, resulting current through the battery, can grow to the level set by P1. When reached this level, the circuit locks and battery voltage drops almost instantly.
LEDs from transistors emitter circuits give a visual indication of connection / disconnection of load current. When the battery is almost fully discharged, the LED will light continuously, and when charging is nearly complete, the load current is interrupted more often, so the LED begins to flash. As is close to fully charged, the faster it will blink.