A DC motor controller have many form, which is difficulty – easy to differently. Today, suggest building a simple two way DC motor control circuit.
It is a H-Bridge that many popular and have high performance.

That H-Bridge motor driver circuit, we will see that are most control circuit to moving of a robot.
We can design the circuit with mosfet or transistor to control rotating of motor. Which I suggest example them as switch, so easy to understand by see its working as Figure 1.

In circuit we see that is the open switch state, no current flowing in circuit cause the dc motor can’t work.
As Figure 2 When have the S1-switch (close) and S3 (close), cause that motor is derived the current, as we notice that current flowing in to the positive terminal of motor, making the dc motor rotated in features of forward form Or rotate clockwise.

Figure 2 the switch-S1 and S3 are close cause motor rotates.

Figure 3 the switch-S2 and S4 are close cause motor rotates back counter clockwise direction.

And If S4 and S2 close together, Motor also get current that flow through them, but will don’t same first form. Because that current will flow through the negative of motor cause current reversed or Rotated back counter clockwise direction. As Figure 3

Start to apply transistors
We will try to use all the transistor as switch. You see in figure 4 . When base is derived current electricity cause transistor running and motor will rotated.

Figure 4 Using the transistor as switches.

Figure 5 we use the four transistors as switch controller.

As Figure 5 we try to take the four to connected into the H-bridge circuit. By we insert a diode to protect the electricity that may flow backward from the motor cause can be damaged the transistor.

Figure 6 apply power into A-point,Q1 and Q3 works,motor rotate forward directions.

In Figure 6 circuit if we apply power to A-point. We will makes Q1 and Q3-transistor works because that get IB-current into base. So, the motor will rotated on forward direction, because that electrical current flowing from Q1 into the positive of motor, and flow through Q3 to ground successfully.

Figure 7 Apply B-point

Then later as Figure 7 we change power supply point into B-point. The Q4, and Q2 also works by they get current from base makes them have current flow through Q4 go to the negative of motor and through Q2-transistors to ground. But flowing of current in this form cause the motor rotated forward there.

More H-Bridge motor driver circuits

You can see real application here The 2 channel DC motor driver on saving model