In this blog, I will be explaining how to use the popular L293D motor driver (often mis-spelt as L239D) along with an Arduino to control the direction and speed of DC motors. I shall also be explaining H-Bridge circuits, which motor drivers like the L293D are based on. This will be very useful in many robotics and electronics projects, so let’s get started!
Role of H-Bridges in Driving Motors
A DC motor (Direct Current motor) is a motor which rotates when a voltage is applied at its terminals. The speed of the motor is proportional to the voltage and direction is dependent on the polarity (direction of current).
Simply put, a DC motor spins when you connect it to a DC power source (like a battery). The greater the voltage, the faster it will spin. If the power source is connected in reverse, the motor will spin in the opposite direction, but with the same speed as before. This is exactly how the speed and direction of a DC motor are controlled.
While the speed control can be done fairly easily by a microcontroller (using Pulse Width Modulation), DC motors usually require more current than most microcontrollers can provide. This is where H-Bridges step in. H-Bridges act as intermediary circuits which allow bi-directional current amplification, allowing the microcontroller to drive the motor in both directions while not getting damaged. Some H-Bridges (Like the L293D) also provide additional pins for more convenient speed control.
You can visualize that the H-Bridge operates between the Microcontroller and the Motor. It supplies power to the motor using an independent power source to which it is connected. However, it is the microcontroller which (through a small current) controls the H-Bridge i.e. the direction and speed of the motor.
The Working of an H-Bridge Circuit
The H-Bridge gets its name from its “H” shaped configuration. Here is how it looks:
It contains four switches (S1-S4) and is connected to a load (Example: motor – M) to be driven. Alternating pairs of switches can be switched on and off to switch the direction of current through the motor, allowing it to spin in both directions. This is how the H-Bridge is used to achieve bi-directional motor control.
In the above diagrams, I have used physical switches, but these can be replaced with transistors. A transistor acts like a switch (capable of connecting or disconnecting circuits), but unlike a regular switch which requires to be physically manipulated, it is dependent on an external current to switch on or off. This allows a microcontroller to control the H-Bridge and drive the motors.
Alternating pairs of transistors are connected together, just like the switches used before, which brings down the pins used to control the motors to two.
While it is possible to construct your own H Bridge using individual transistors, in this blog I will be using the L293D (often mis-spelt as L239D) as it is compact, popular and comes in many different breakouts (as well as the IC alone).
Here is what it looks like:
Configuration and working of the L293D IC
The L293D is a very popular H Bridge IC. Internally, it contains two H Bridges allowing you to individually drive 2 motors bidirectionally up to 36V at 0.6A each (1A for short spurts). It also contains two additional pins for more convenient speed control (explained in detail later).
Each side of the IC can be used individually to drive a load bi-directionally.
Power & Grounding: Pins 16 (VSS) and 8 (VS) need to be connected to the positive terminal of your power supply which will be used to drive the load. Pins 4, 5, 12 or 13 (all are GND) need to be connected to the negative terminal. Optionally, they can also be used to solder a heat sink onto the chip. The four ground pins are connected to each other and connecting even one of them is enough, however it is recommended to connect wires to all of them to manage heating issues better.
Controlling the Direction: Pins 2 and 7 (INPUT 1 and 2) are used for controlling the states of pins 3 and 6 (OUTPUT 1 and 2) which get connected to the load such as a motor. The state of each input pin reflects the state of its respective output pin. For example, setting the state of pin 2 (INPUT 1) and 7 (INPUT 2) to high and low respectively will cause pins 3 (OUTPUT 1) and 6 (OUTPUT 2) to be set to high and low respectively and vice-versa. In other words, current can flow in either direction by reversing the states of the INPUT pins. These pins are the alternating switches of the H-Bridge.
Similarly, pins 10 and 15 (INPUT 3 and 4) are used for controlling pins 11 and 14 (OUTPUT 3 and 4), allowing a second load to be connected and driven independent of the first.
Controlling the Speed: There exist to special pins on the L293D called the enable pins – Pins 1 and 9 (ENABLE 1 and 2). Setting an enable pin to high, switches on or “enables” its respective H Bridge circuit while setting it low, breaks the circuit.
They can be provided with a PWM signal with varying duty cycles to control the speed of the motors. If you are not familiar with how PWM works, click here for my tutorial on the same.
Circuit for Arduino, L293D and Motors
In this section, I will be showing how to assemble a test circuit to drive a single motor using an Arduino UNO and the L293D. Here is a list of the components you will require-
- An Arduino UNO (any alternate Arduino or equivalent microcontroller will work)
- A DC motor
- The L293D H-Bridge
- A breadboard
- A suitable power supply to drive your motor (I have used a 9v battery)
If you are not familiar with Arduino, then you can click here to go to my tutorial on getting started with Arduino.
First connect the pins of your power supply to the L293D. This includes the positive and negative pins. The positive supply goes to the VSS and VS while the negative goes to GND as shown-
Next, connect the motor to the output pins of the IC as shown-
Finally, connect two digital pins of the Arduino to the input pins of the IC (on the same side as the motor) and a third pin (PWM capable) to the enable pin of the IC for speed control. The PWM capable pins are marked with a tilda symbol (~) before them. I have used pins 7, 8 and 9.
The red and black wires coming out of the battery indicate positive and negative polarity respectively. The red and black wires going to the motor represent the polarity to turn the motor in the clockwise direction (i.e. to spin the motor in the clockwise direction, current must flow from the red wire to the motor and out of the black wire). The green and yellow wires are the direction control wires while the brown wire is for speed control.
This completes the circuit assembly.
Program to drive motors via L293D
In this section I will be showing and explaining the code to drive the circuit asembled above. It will accelerate the motor from stationary to maximum speed, de-accelerate it and repeat this in the opposite direction, with this whole cycle repeating indefinitely. This uses the complete functionality of the motor driver.
Start by defining the pins you will be using to drive the motors****. In the above circuit I have used pins 7, 8 and 9 and will be defining them as IN1, IN2 and EN. Next, set each of their pin-modes to output in the setup.
Next, create functions which will be used to change the speed and direction of the motors. The speed control function takes an integer value between 0 and 255 its parameter and sets EN to the given value. The direction control function takes a boolean value (either High or Low) as its parameter and sets one IN1 to the given value and IN2 to the inverse of this value (High becomes Low and Low becomes High).
Finally, in the main loop, create four for loops, two going from 0 to 255 and two from 255 to 0, alternating between the two. Before each pair of for loops, set the direction of the motor. In each iteration of the loop, change the speed of the motor to match the state of the loop. Also add a small delay (I have used 15 milliseconds) in each loop to make sure you can see the changes.
The complete code should look a bit like this-
Now, you can compile and upload your program and if everything was done right, the motor should start spinning! That’s it, you’re done!
As I have said, L293D has the capability to control not just one but two motors. You may try to control two motors with the Arduino simultaneously, with both of them spinning at different speeds, in different directions.
If you found this blog helpful, leave a comment down below. I would love to know your thoughts!