AVR Programming for DC Motor Interfacing (1)

7/28/2019 AVR Programming for DC Motor Interfacing (1)

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DC Motor interfacing with Microcontrollers tutorial: Introduction

Introduction

Whenever a robotics hobbyist talk about making a robot, the first thing comes

to his mind is making the robot move on the ground. And there are always twooptions in front of the designer whether to use a DC motor or a stepper motor.When it comes to speed, weight, size, cost... DC motors are always preffered

over stepper motors. There are many things which you can do with yourDC

motor when interfaced with a microcontroller. For example you can control the

speed of motor, you can control the direction of rotation, you can also doencoding of the rotation made by DC motor i.e. keeping track of how many

turns are made by your motors etc. So you can see DC motors are no less than

a stepper motor.

In this part of tutorial we will learn to interfacing a DC motor with a

microcontroller. Usually H-bridge is preffered way of interfacing a DC motor.These days many IC manufacturers have H-bridge motordrivers available in the

market like L293D is most used H-Bridge driver IC. H-bridge can also be madewith the help of trasistors and MOSFETs etc. rather of being cheap, they only

increase the size of the design board, which is somtimes not required so using

a small 16 pin IC is preffered for this purpose.

Working Theory of H-Bridge

The name "H-Bridge" is derived from the actual shape of the switching circuit

which control the motoion of the motor. It is also known as "Full Bridge".

Basically there are four switching elements in the H-Bridge as shown in thefigure below.

As you can see in the figure above there are four switching elements named as

"High side left", "High side right", "Low side right", "Low side left". Whenthese switches are turned on in pairs motor changes its direction accordingly.

Like, if we switch on High side left and Low side right then motor rotate in

forward direction, as current flows from Power supply through the motor coil

goes to ground via switch low side right. This is shown in the figure below.

Similarly, when you switch on low side left and high side right, the current

flows in opposite direction and motor rotates in backward direction. This is the


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basic working of H-Bridge. We can also make a small truth table according to

the switching of H-Bridge explained above.

Truth Table

High Left High Right Low Left Low Right Description

On Off Off On Motor runs clockwise

Off On On Off Motor runs anti-clockwise

On On Off Off Motor stops or decelerates

Off Off On On Motor stops or decelerates

As already said, H-bridge can be made with the help of trasistors as well as

MOSFETs, the only thing is the power handling capacity of the circuit. If

motors are needed to run with high current then lot of dissipation is there. Sohead sinks are needed to cool the circuit.

Now you might be thinkin why i did not discuss the cases like High side lefton and Low side left on or high side right on and low side right on. Clearlyseen in the diagra, you don't want to burn your power supply by shorting them.

So that is why those combinations are not discussed in the truth table.

So we have seen that using simple switching elements we can make our own

H-Bridge, or other option we have is using an IC based H-bridge driver. Both

of them are discussed in the next section of the tutorial.

Previous Page | Next Page

DC Motor Tutorial IndexDC Motor Introduction Interfacing L293D

BJT Based H-Bridge Programming for DC Motor

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DC Motor

interfacing with Microcontrollers tutorial: BJT Based H-Bridge for DC motors

BJT H-Bridge

A simple H-bridge can be made with the help of Power BJTs like TIP31 and TIP32. An example

and a working demo of this circuit is shown in the figure below.

BJT H-Bridge Demo


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// Function Prototypesvoi d rotate_f( voi d) ; //Forward run funtionvoi d rotate_b( voi d) ; //Backward run functionvoi d br eaks( voi d) ; //Motor stop function

voi d del ay( voi d) ;//Some delay

voi d mai n( ) { //Our main functionwhi l e( 1) { //Infinite loop

rotate_f( ) ; //Run forwarddel ay( ) ; //Some delaybr eaks( ) ; //Stopdel ay( ) ; //Some delayrotate_b( ) ; //Run Backwardsdel ay( ) ; //Some delaybr eaks( ) ; //Stopdel ay( ) ; //Some delay

} //Do this infinitely}

voi d rotate_f( ) {L293D_A = 1; //Make positive of motor 1L293D_B = 0; //Make negative of motor 0L293D_E = 1; //Enable L293D

}

voi d rotate_b( ) {L293D_A = 0; //Make positive of motor 0

L293D_B = 1; //Make negative of motor 1L293D_E = 1; //Enable L293D

}

voi d br eaks( ) {L293D_A = 0; //Make positive of motor 0L293D_B = 0; //Make negative of motor 0L293D_E = 0; //Disable L293D

}

voi d del ay( ) { //Some delay...

unsi gned char i , j , k;f or ( i =0; i


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As you can see in the circuit, three pins are needed for interfacing a DCmotor (A, B, Enable). If you want the o/p to be enabled completely then

you can connect Enable to VCC and only 2 pins needed from controller

to make the motor work.

As per the truth mentioned in the image above its fairly simple toprogram the microcontroller. Its also clear from the truth table of BJT

circuit and L293D the programming will be same for both of them, just

keeping in mind the allowed combinations of A and B. We will discuss

about programming in C as well as assembly for running motor withthe help of a microcontroller.


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AVR Programming for DC Motor Interfacing (1)