To get DC current from electric generator we replace slip rings in AC generator with a split ring type commutator (like the one used in electric motor). In this arrangement one brush will always be in contact with the arm moving up in the field and the other brush will always be in contact with the arm moving down. Hence, the unidirectional current is produced i.e. direct current.
The schematic diagram of the generator is as follows:
DC generator consists of a regular coil MNST of insulated copper wire placed in a magnetic field produced by two strong magnetic poles. The two ends of the coil are connected to the two halves C and D of split rings. The inner sides of these halves are insulated and attached to an axle X and the external conducting edges touch two conducting brushes A and B.