Controlling DC Motors with the L298N Dual H-Bridge and an Arduino

If you plan on working with robots or just building things that move you’ll eventually need to learn how to control a DC motor. The inexpensive L298N H-Bridge module is a simple way to achieve that. Coupling the L298N H-Bridge to a microcontroller like an Arduino will give you the ability to control both the speed and rotation direction of two DC motors.

In this article and it’s accompanying video I’ll show you everything you need to know to start adding some motion to your next Arduino project. So let’s get moving!

 

DC Motors

The first practical DC (Direct Current) motor was invented by the British scientist William Sturgeon in 1832. Since then DC motors have been part of countless pieces of equipment and machinery.

Today DC motors range from huge models used in industrial equipment to tiny devices that can fit in the palm of your hand. They are inexpensive and are ideal for use in your Robotics, Quadcopter, and Internet of Things projects.

Unlike LED’s you can’t just connect a DC motor to one of the output pins of your Arduino or Raspberry Pi and expect it to work. DC motors have current and voltage requirements that are beyond the capabilities of your microcontroller or microcomputer. It is necessary to use some external electronics to drive and control the motor, and you’ll probably need a separate power supply as well.

There are a number of ways to drive a DC motor from the output of your computing device. A single transistor can be used to drive a DC motor, this works well providing you do not need to change the direction that the motor is spinning.

A more versatile way of controlling a DC motor is to use a circuit called an “H-Bridge”. An “H-Bridge” is an arrangement of transistors that allow you to control both the direction and speed of the motor. Today we’ll examine a very common H-Bridge module based around the L298N integrated circuit.

How DC Motors Work

In a simple DC motor there are two main components, the “stator” and the “armature”. The stator is a permanent magnet and provides a constant magnetic field. The armature, which is the rotating part, is a simple coil.

The armature is connected to a DC power source using a 2-piece ring installed around the motor shaft, these ring sections are called “commutator rings”. The two pieces of the commutator rings are connected to each end of the armature coil. Direct Current of a suitable voltage is applied to the commutator rings via two “brushes” that rub against the rings.

When DC is applied to the commutator rings it flows through the armature coil, producing a magnetic field. This field is attracted to the stator magnet (remember, opposite magnetic polarities attract, similar ones repel) and the motor shaft begins to spin.

The motor shaft rotates until it arrives at the junction between the two halves of the commutator. At that point the brushes come into contact with the other half of the commutator rings, reversing the polarity of the armature coil (or coils, most modern DC motors have several). This is great because at this point the motor shaft has rotated 180 degrees and the magnetic field polarities need to be reversed for the motor to continue rotating. This process repeats itself indefinitely until the current is removed from the armature coils.

The motor I have just described is referred to as a brushed DC motor because (obviously) it has brushes. Brushes, however, create many problems – they can start to wear over time, they rub against the motor shaft and they can even cause sparking as the motor gets older.

Better quality DC motors are the brushless variety. Brushless motors use a more complex arrangement of coils and do not require a commutator. The moving part of the motor is connected to the permanent magnet. Because they do not contain brushes these brushless motors will last longer and are also much quieter than brushed DC motors. Most quadcopter Motors are brushless motors.

DC motors are specified by the voltage level at which they operate. Common hobbyist motors run at 6 Volts or 12 volts DC.

To reverse the direction in which the DC motor rotates you simply reverse the polarity of the DC current that you apply to it. Changing the speed however, is a different story.

One method of changing the speed of a DC motor is to simply reduce its supply voltage. While this will work to some degree it is actually not a very good method of controlling motor speed as lowering the voltage will also lower the torque that the motor is capable of producing. Also, once the voltage drops below a certain point the motor will not rotate at all.

Pulse Width Modulation (PWM)

A far better method of controlling DC motors is to use pulse width modulation or PWM. If you’ve read up on controlling LEDs with your microcontroller you probably have already run into PWM as it’s also a good method of controlling the brightness of an LED.

With PWM the motor is sent a series of pulses. Each pulse is of the full voltage that the motor can handle so a 6-volt motor will be sent 6-volt pulses while a 12-volt motor will be sent 12 volt pulses. The width of the pulses are varied to control the motor speed, pulses with a narrow width will cause the motor to spin quite slowly. Increasing the pulse width will increase the speed of the motor, as illustrated below.

In order to stop the motor completely you just stop pulsing it, essentially sending it zero volts. To run it at full speed you send it the full voltage, again without pulsing it.

You can build a simple PWM generator using a 555 timer and discrete components but it’s a lot easier to use an Arduino. The Arduino has a function called “analogWrite” which is used to drive any of its PWM-capable outputs (the Arduino Uno has 6 digital outputs that are also capable of PWM).

H-Bridge

Now that you know how DC motors work, how you can reverse their direction by changing polarity and how you can change their speed using pulse width modulation, let’s examine an easy way to do this using a very common circuit configuration called an “H-Bridge”.

An “H-Bridge” is simply an arrangement of switching the polarity of the voltage applied to a DC motor, thus controlling its direction of rotation. To visualize how this all works I’ll use some switches, although in real life an H-Bridge is usually built using transistors. Using transistors also allows you to control the motor speed with PWM, as described above.

In the first diagram we can see four switches which are all in the open or “off” position. In the center of the circuit is a DC motor. If you look at the circuit as it is drawn here you can distinctly see a letter “H”, with the motor attached in the center or “bridge” section – thus the term “H-Bridge”.

If we close (i.e. turn on) two of the switches you can see how the voltage is applied to the motor, causing it to turn clockwise.

Now we’ll open those switches and close the other two. As you can see this causes the polarity of the voltage applied to the motor to be reversed, resulting in our motor spinning counterclockwise.

This is pretty simple but effective. In fact if all you need to do is design a circuit to drive the motor full-speed in either direction you could actually build this as shown here, using a 4PDT (4 Pole Double-Throw) center-off switch. But of course we want to control the motor using an Arduino, so an electronic circuit where the switches are replaced by transistors is what we need.

The L298N H-Bridge

While you can use discrete transistors to build an H-Bridge there are a number of advantages in using an integrated circuit. A number of H-Bridge motor driver IC’s are available and all of them work in pretty much the same fashion. One of the most popular is the L298N.

The L298N is a member of a family of IC’s that all have the designation “L298”. The difference between the family members is in the amount of current they can handle. The L298N can handle up to 3 amperes at 35 Volts DC, which is suitable for most hobby motors.

The L298N actually contains two complete H-Bridge circuits, so it is capable of driving a pair of DC motors. This makes it ideal for robotic projects, as most robots have either two or four powered wheels. The L298N can also be used to drive a single stepper motor, however we won’t cover that configuration in this article.

Here is a diagram of the pinouts of an L298N integrated circuit:

Although you can certainly purchase an L298N integrated circuit and wire it up yourself it is far easier to just buy a complete L298N circuit board, which is wired up and complete with connectors for motors, power supplies and input logic. These boards also have a 5 volt voltage regulator which can be used to supply the logic circuits. L298N driver boards are available from a number of sources like eBay or your local electronics shop at very reasonable prices.

L298N Module Pinouts

You’ll find a few different styles of L298N boards but they all operate in the same fashion. The board contains an L298N mounted on a heatsink, a 5 volt voltage regulator to “optionally) provide power for logic circuits, supporting diodes and capacitors and connectors as follows:

• Logic inputs for each H-Bridge circuit
• Power supply inputs for the motor power supply
• An optional 5 Volt power input for the logic circuits.
• Outputs for each DC motor

A typical L298N Board is shown here.

You’ll notice that the board also has a number of jumpers. Most of the time you will leave them in place, with the exception of one. They are as follows:

• CSA – This is the “current sensing” function for Motor A. If the jumper is in this function is ignored. Most of the time you’ll leave this jumper in place.
• CSB – The “current sensing” function for Motor B. Again you’ll usually just leave this in place to disable this function.
• U1 – Input 1 pull-up resistor. You will usually leave this in place, which enables a 10k pull-up resistor for the input.
• U2 – Input 2 pull-up resistor.
• U3 – Input 3 pull-up resistor.
• U4 – Input 4 pull-up resistor.
• 5v-EN – This is the only jumper that you need to really pay attention to. When this jumper is in place it enables the boards internal 78M05 5 Volt regulator, supplying logic power from the motor power supply. When this jumper is enabled you will NOT supply 5 volts to the 5 Volt input terminal. When the jumper is removed you will need to supply 5 Volts to the 5 Volt input terminal.

If you do use the internal voltage regulator you’ll have to supply the motor power supply with at least 7.5 volts.

Speaking of the motor power supply it needs to be a bit higher voltage than the actual motor requirements. This is due to the internal voltage drop in the transistors that form the H-Bridge circuit. The combined voltage drop is 1.4 volts, so if you are using 6 Volt motors you’ll need to give the board 7.4 volts, if you have 12 volt motors then your motor supply voltage will need to be 13.4 volts.

The board has four input terminals plus two enable terminals. You will use these terminals to control both direction and speed or each motor. They are as follows:

• IN1 – Input 1 for Motor A
• IN2 – Input 2 for Motor A
• IN3 – Input 3 for Motor B
• IN4 – Input 4 for Motor B
• EN1 – Enable line for Motor A
• EN2 – Enable Line for Motor B

In order to simplify things a bit I’ll just discuss the inputs and enable for Motor A, Motor B functions identically.

The two Input lines control the direction that the motor rotates. I will call one direction “forward” and the other one “reverse”, if it makes more sense to you just substitute “clockwise” and “counterclockwise”.

You control motor direction by applying either a Logic 1 (5 Volts) or Logic 0 (Ground) to the inputs. This chart illustrates how this is done.

 

INPUT 1	INPUT 2	DIRECTION
Ground (0)	Ground (0)	Motor Off
5 Volts (1)	Ground (0)	Forward
Ground (0)	5 Volts (1)	Reverse
5 Volts (1)	5 Volts (1)	Not Used

As you can see only two combinations are actually used to control the direction of the motors rotation.

The Enable line can be used to turn the motor on, to turn it off and to control its speed. When the Enable line is at 5 Volts (1) the motor will be on. Grounding the Enable line (0) will turn the motor off.

To control the speed of the motor you apply a Pulse Width Modulation (PWM) signal to the Enable line. The shorter the pulse width, the slower the motor will spin.

Breadboard Experiments

We can use a solderless breadboard, a pair of motors and a few jumpers to test the L298N module.

You’ll also need a power supply for the motors. In my experiment I used a second power supply to supply the 5 Volts for the logic circuitry but you could use one supply for both the motors and logic if you wish. Just be sure to set the 5 Volt Jumper properly (if you use one supply it should be in place, if you use two like I did remove the jumper).

The initial hookup looks like this:

Note that both the motor and logic power supplies share a common ground. I’ve brought the 5 Volt supply with ground out to the solderless breadboard so it can be used to set logic levels.

To get things moving we will need to set the logic levels on the input and enable lines. In our first experiment we will set EN1, IN1 and IN3 to 5 Volts. The remaining inputs and enable line will be tied to ground.

This arrangement will cause Motor A to move in a forward direction. As the enable line for Motor B is at ground it will remain off.

Now let’s enable Motor B by setting EN2 to 5 Volts.

As you might expect this causes both motors to rotate in a forward direction.

Now we will change the inputs for Motor A, we will set IN1 to ground and IN2 to 5 Volts. The other connections will remain as they are.

If you understood the chart I showed you earlier with the input logic levels you won’t be surprised to see Motor A now moving in reverse. Motor B continues to move forward.

You can use this arrangement to experiment with controlling the motor direction, as well as enabling and disabling the two motors. But one thing that you can’t test this way is controlling motor speed. For this we will need to apply a PWM signal to the Enable lines. There are a number of ways of accomplishing this, for our next experiment we will do it using an Arduino.

Using an Arduino with the L298N

Bringing an Arduino or similar microcontroller into the picture allows us to control both the direction and speed of each motor. I am going to show you how to do this using an Arduino Uno but you can also accomplish the same thing with a Mega, Nano or other Arduino compatible controller.

The Arduino Uno has 14 digital Input/Output (I/O) pins, six of which are capable of supplying a PWM signal.
The following diagram shows how I have hooked up the Arduino Uno to the L298N board.

Note that the 5 Volts for the L298N board is now being supplied from the Arduino 5 Volt output. The Arduino itself is being powered via its USB cable, which of course will also allow you to load the sketch to make everything work. After the sketch is loaded you could remove the USB cable and power the Arduino with an external power supply (or a USB supply).

The input and enable lines in the L298N are driven from six Arduino digital output pins, as follows:

 

Arduino	L298N
9	EN1
8	IN1
7	IN2
5	IN3
4	IN4
3	EN2

 

I chose this pinout as Arduino output pins 9 and 3 are both capable of Pulse Width Modulation, if you wish you can use alternate pins. Just be sure to modify the sketch to reflect any pinout changes you make.
Speaking of the sketch, here it is:

This sketch demonstrates a number of things we can do to control an L298N H-Bridge with an Arduino. You can play around with it to see what effects changing some values have and you can also use sections of it as the basis for other motor control sketcheds you want to create. It could also be used with other H-Bridge controllers as they all operate in a similar fashion.

We start out by defining integers to represent the digital output pins that will be used to drive the H-Bridge controller.  This is good coding practice as it allows you to change pin numbers by just changing these values, allowing you to use the same sketch with different Arduinos. Just remember that the two enable pins, defined as enA and enB, need to be connected to outputs that support PWM.

In the setup function we define all of these pins as digital outputs.

After that we define two functions. Once you understand how they work feel free to add more if you wish.

• demoOne – this function spins both motors forward as a speed of 200 for two seconds. It then reverses the motors and spins them for another two seconds. Finally it turns off the motors.
• demoTwo – this function spins the motors forward. First it accelerates them from zero to full speed, then it decelerates them back to zero. Again it turns the motors off when it is done.

In each of these functions Arduino’s analogWrite function is used to produce PWM signals at the digital outputs. If you plan on working with PWM it’s a very good function to know.

In the loop we just call the two functions, inserting a one second delay between them. This continues until you power off the Arduino.

Adding Speed Controls

Now that we have the L298N H-Bridge controller working with the Arduino let’s expand upon it. Our demo sketch really isn’t that practical, especially if we are using our motors to drive a robot or toy car. What we really need is a way to take control ourselves. So let’s add some speed controls to our design.

Take a look at the following diagram. Essentially we’ve taken the same circuit and have added a couple of potentiometers. Each potentiometer has one end tied to ground, the other end hooked to 5 volts and the wiper connected to an analog input pin ou the Arduino. The value of the potentiometers isn’t that critical, I used 25k pots as I happened to have a bunch of them but any value from 10k up would work. Going lower than 10k wouldn’t be a good idea though as that would start to consume a bit too much current from the Arduino 5 volt output.

The Arduino Uno has 8 analog input pins and again it really doesn’t matter which ones we use – if you decide to be daring and change pins simply modify the sketch accordingly. I used the first two – Potentiometer A is connected to analog input A0 while potentiometer B goes to analog input A1.

Turning the pots will vary the voltage applied to the inputs from zero to 5 volts. In our sketch we will read these values as numbers from 0 to 1023 (the Arduino Uno has internal 10 bit analog to digital convertors).

Here is the sketch that I used to take the analog values from the potentiometers and use them to control the motor speed.  Note that in this sketch I haven’t made any provision to change motor direction.

Let’s take a look at this sketch.

We begin in a similar fashion to our motor demo sketch, defining integers to represent output pins to control our H-Bridge. We also define a couple more integers for the analog inputs that we will use for the potentiometer inputs to A0 and A1. Again you can rewire to use other inputs and change this section of the sketch accordingly if you wish.

Another set of integers are also defined, MotorSpeed1 and MotorSpeed2. As their name implies these will hold the values to use to control the motor speeds for each motor. We initialize these with a value of zero so that our motors start out stationary.

In setup we simply set all the digital pins we defined earlier as outputs.  No equivalent definition for the analog inputs is necessary as by nature these are always inputs.

Now on to the loop. We start by setting the direction of both motors forward which is done by writing the proper values to the H-Bridge input pins.

Next we read the values of each potentiometer using the analogRead function. As the Arduino uses an 10-bit A/D convertor this will produce a value ranging from zero to 1023, which is held in each MotorSpeed variable..

We need to convert these MotorSpeed values to a range of 0 – 255 and there are a few ways we could accomplish this. One method is to divide the values by 4, and this would work fine (try it an see). But a more eloquent method is to make use of Arduinos map function which takes a range of values and converts this to a different range of values. It’s a very handy function that you should get to know if you are not familiar with it.

In experimenting I found that my motors started to “buzz” or “sing” when fed very low PWM values (you may have noticed this during the demo sketch). To keep from this annoyance from occurring I popped a couple of if statements into the code to set any value below 8 to zero. You may need to adjust this value to suit your specific motor/ controller combination.

Finally the analogWrite function is used to produce PWM pulses to the enable pins on the L298N H-Bridge Motor Controller.

This is actually a practical sketch and circuit as it allows us to control each motors speed independently using the two potentiometers. But it doesn’t allow us to control teh motor direction. This leads us to our final experiment, one that turns all that we learned into a practical arrangement for driving a small 2-motor robot car.

Control with a Joystick

Our circuit is now a lot more practical but it still lacks a simple way to change motor direction. We could use one of the unused digital pins on the Arduino as an input for a switch to solve this problem, but I thought it might be a bit more fun to use a joystick. If the two motors are mounted on a small toy car or robot base then the joystick would provide a fun way to drive our vehicle around the room!

A joystick actually consists of three parts. First there are two potentiometers, one on the horizontal axis and the other on the vertical axis. The third part is a momentary contact switch (i.e a pushbutton) that is activated when you press down on the joystick handle.

Joysticks usually have five connections:

• Vcc – This is the +5 Volt connection
• Gnd – The Ground connection
• Vert – The Vertical potentiometer wiper. Sometimes labelled “Y-Axis”
• Horiz – The Horizontal potentiometer wiper. Sometimes labelled “X-Axis”
• Sel – The output from the momentary contact switch

Please note that there are a variety of joysticks available and no apparent standard for ordering or labelling the connections. Be sure you know what connection goes where before you wire up your joystick. If you’re not sure and can’t find a hookup diagram you can usually determine the connections using a multimeter.

Once you’ve sorted out your joystick connections you can remove the two potentiometers we used in the last experiment and hook up the joystick as shown here.

 

The only real difference between this circuit and the previous one is that the joysticks’ internal potentiometers take the place of the two discrete potentiometers we used before.  I chose not to use the pushbutton switch, if you wish you could tie it to an unused Arduino input pin and use it to beep a piezo buzzer or flash an LED. I’ll leave the customizing up to you!

The real fun with this setup lies in the sketch. Before we examine it let’s discuss how our project will work.

• With the joystick resting in its center position the motors will be disabled. In our last experiment the only way to actually stop the motors was to set the speed to zero or unplug the power from the Arduino, not very convenient!
• Pushing the joystick forward (i.e up) should move our car forward.
• Pulling the joystick backward (i.e down) should make the car move backwards.
• As we push the joystick to one side the car should respond by moving in that direction. We’ll do this by making one motor move faster than the other one.
• Letting the joystick come to rest in the center position should stop the car.

The sketch I came up with to accomplish all this is as follows:

Let’s examine how the sketch works.

The sketch starts in a similar fashion to the one we used previously,integers are defined to represent the input pins for the motor input and enable lines.  The two analog inputs are defined as “joyVert” (the joystick vertical or Y axis output) and “joyHorz” (the horizontal or X axis output).  Once again the tow “MotorSpeed” integers represent the speed of each motor and are initially set to zero.

I’ve also defined two integers to represent the value of each joystick axis position. Each has a range of 0 to 1023, so the middle position of each is approximately 512 (it’s actually 511.5, but as we are using integers I selected 512).

In the setup function the pins controlling the L298N H-Bridge controller are set as outputs and the motors are initialized as being disabled and with their directions set forward.

Now to the loop, where the real action is!

First thing we do is get the position of each joystick potentiometer by reading the value of the two analog input pins.  We will use these values to determine what direction and speed we want our car to travel in. Keep the following bits of information in mind so that you understand the logic here:

• The vertical or Y axis control determines if we are going forward or backwards, and how fast.  As we push it up we are going forward, pulling it down indicates we want to go backwards. The further to the end we push, the faster we want to go.  If we center the joystick then we want the motors to stop.
• The horizontal or X axis control determines if we are moving to the left or right. Keep in mind that to move in one direction you need to spin the opposite motor faster! So, for example, if I want to turn left I need to decrease the speed of the left motor and increase the speed of the right motor.  If this control is centered then both motors should revolve at the same speed.

Now that we have these concepts firmly in place let’s see how it’s accomplished in the sketch.

If our two joystick potentiometers are in the center position then we don’t want to move either motor.  As I mentioned earlier the center positions should produce a value on our analog inputs of about 512, however in the real world the actual value will be “around 512” as the tolerances in the components isn’t perfect. I chose to allow plus or minus 10 percent, so I consider any value between 460 and 564 to be defined as “center”. You can experiment with these values if you wish to “fine tune” things to your own joystick.

So if the vertical potentiometer is less than 460 then we need to get it’s value and translate it into a speed, as well as move our motors backwards.

Moving the motors backwards is simply a matter of setting the H-Bridge inputs properly, as we have done already.  Getting the speed however requires a little bit of math, since we need the speed to increase when the analog input value decreases. No worries, as it’s fairly basic math – we just subtract 460 from the value of the analog input which gives us a negative number, then we convert this to a positive number by multiplying by negative one.

Finally we get the number in our desired range of 0-255 using the handy “map” function as we did in the previous sketch.

If the vertical potentiometer is reading over 564 then we are going forward. The logic here is easier as the value goes up while the speed increases, so the “fancy math” isn’t required. Again we map these values to the range of 0-255.

Now for the steering, which is controlled by the horizontal or X-axis potentiometer.  Remember how this works:

• We’ll be modifying the motor speed values we obtained using the vertical (Y-axis) analog inputs, adding or subtracting from them to make our car turn in the desired direction.
• If the analog input value is less than 460 then we want to go to the left. The lower the value, the more to the left we want to turn
• If the analog input value is over 564 then we want to turn right. In this case the higher the value the more to the right we want to go.
• If the value is between 461 and 563 then we don’t want to turn in either direction.
• Whatever we do the motor speed value cannot drop below zero or exceed 255.

With this in mind the code should make sense. Note that this section does not use an “else” statement like we did for the vertical control, since if the potentiometer is in our defined center range there is nothing we need to do.

Finally we finish the sketch like we did earlier, adjusting values below 8 to zero so that the motors don’t “buzz” at extremely low speeds and then finally writing the values out to the two motor enable lines so that we can control the motor speeds with our L298N H-Bridge controller.

Summary

We have covered a lot of ground in this article and its accompanying video. We’ve learned how a DC Motor works, what an H-Bridge is and how we can use the L298N H-Bridge controller with (and without) and Arduino.  We also examined Pulse Width Modulation, an important concept in motor control as well as a number of other applications. We even built a crude but functional robot car with a joystick control. Not bad for a few hours of work!

Other H-Bridge controllers operate in a similar fashion so you can now take your newfound knowledge and apply it to them as well. So whether you want to control some tiny motors or a couple of massive ones you are now prepared. Your imagination is the only limit, so get out your Arduino and make some things move!