Simple and easy automatic charger

This charger has a simple circuit and easy-to-access components. It charges each nickel-cadmium battery separately and stops automatically when fully charged. The circuit is shown in the attached figure. Before charging, adjust R4 first so that the output voltage of the three-terminal adjustable voltage regulator LM317 is the predetermined value Vo. When the voltage Ve of the rechargeable battery rises to Vo-0.65V, the transistor is turned off and charging is terminated. , and the corresponding charging indicator LED goes out. Its charging current is limited by R11-R14.