Above circuit shows relay driver to operate two DC motors simultaneously. the current driver chip ULN2003A is used to supply enough current to relay coil (max 500 mA per pin). as shown in figure inputs A, B, C and D are coming from 89C51 (P2.4-P2.7). Total four relays are used two are single change over (C/O) RL1 & RL3 and other two are 2 C/O RL4 & RL2. RL1 and RL3 are used to ON and OFF DCM1 / DCM2 while RL2 and RL4 are used to change the direction of DCM1 / DCM2. thus together RL1 and RL2 runs or stops DCM1 and also alters directions of DCM1. in same manner RL3-RL4 is for DCM2. So by switching ON / OFF these four relays one can get the motion of moon walker in all four direction. Please refer the table.

motion	RL1	RL2	RL3	RL4
forward	ON	OFF	ON	OFF
reverse	ON	ON	ON	ON
left turn	ON	OFF	OFF	OFF
right turn	OFF	OFF	ON	OFF