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 two options 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 your DC 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 do encoding 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 motor drivers available in the market like L293D is most used H-Bridge driver IC. H-bridge can also be made with 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 the figure below.

Basic H-bridge

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". When these 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.

Motor rotation in forward direction

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 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. So head sinks are needed to cool the circuit.

Now you might be thinkin why i did not discuss the cases like High side left on and Low side left on or high side right on and low side right on. Clearly seen 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.

Conversation

ajay_bhargav
Mon Oct 20 2014, 11:22 AM
@skrishna, please post in forum so we can help you better.
Tue Oct 14 2014, 01:45 PM
skrishna
how do i write an ALP equivalent 7segment display interfacing embedded c program (both 8051 microcontroller)
Sat Oct 11 2014, 06:41 PM
vaidehi
want details of seven segment LED display common cathode ( IC CD 4026)
Fri Oct 03 2014, 12:52 PM
Narsim
Rickey you inspired me a lot ... I am also planing like you ...
ExperimenterUK
Wed Oct 01 2014, 09:33 PM
We're back.. we had a bug, but posting is back to normal
ExperimenterUK
Sat Sep 13 2014, 04:34 PM
jaimin1212,Pimpalkhare Create a thread for your question
jaimin1212
Sat Sep 13 2014, 06:35 AM
i want to make self balancing robot using MPU6050 using atmega8.. please help to get data of gyro and accelerometer from this sensor through atmega8.
Thu Sep 11 2014, 01:00 PM
Sunil Pimpalkhare
Hello sir, I am trying to make Wearfin project https://www.youtube.com/watch?v=iZ6PVBvQf-g so can u help me in teaching how to built the program???
Thu Sep 11 2014, 06:21 AM
hariom panday
plz hlp me in my project
iec.naga
Tue Sep 09 2014, 05:19 AM
spi

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pddung93
Sun Oct 19 2014, 01:56 PM
msideal
Thu Oct 16 2014, 08:48 AM
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Tue Oct 14 2014, 06:23 PM
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Mon Oct 13 2014, 05:48 AM
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Mon Oct 13 2014, 02:47 AM
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ajay_bhargav Avatar
Posted By ajay_bhargav
Mon Oct 20 2014, 11:19 AM
Use a 8bit shift register with latch control (e.g....
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Posted By ajay_bhargav
Mon Oct 20 2014, 11:17 AM
You can use the attach file button to attach the i...
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Posted By ajay_bhargav
Mon Oct 20 2014, 11:12 AM
I think you need to first check your code what exa...
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Posted By ajay_bhargav
Mon Oct 20 2014, 09:11 AM
I don't have resources to show this but if I get t...
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Posted By ajay_bhargav
Mon Oct 20 2014, 09:09 AM
Initialise _data in the header file to some value ...
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Posted By ajay_bhargav
Mon Oct 20 2014, 09:07 AM
8051 is slow in doing what? Well I don't think 805...
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Posted By ajay_bhargav
Mon Oct 20 2014, 09:00 AM
I also checked in Intel manual however I could not...
msideal Avatar
Posted By msideal
Sun Oct 19 2014, 07:25 PM
Is there anyone who could help me in solving this ...
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Posted By jona
Sun Oct 19 2014, 02:03 AM
Has anyone used this device? I was able to get the...
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Posted By kirangowle
Sat Oct 18 2014, 03:49 PM
Thanks ExperimenterUK