Hey friends this is my 3rd year BE project " Speed control of DC motor"which i could like to share with you .In this you will learn how to interface LCD,hex keypad and motor .The code is written in assembly      
to simplify I have first explained separately LCD interfacing hex keypad interfacing ,motor interfacing with L293D 

so Lets get Started !!!
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Step 1: Materials required

Picture of Materials required
*Hex keypad
*DC motor 

I assume u have basic knowledge of 8051 programming in assembly

Step 2: Interfacing DC motor -L293D

Picture of interfacing DC motor  -L293D
L293D is a dual H-Bridge motor driver, So with one IC we can interface two DC motors which can be controlled in both clockwise and counter clockwise direction we can control speed of each dc motor by giving PWM to enable pin .L293D has output current of 600mA and peak output current of 1.2A per channel. Moreover for protection of circuit from back EMF ouput diodes are included within the IC. The output supply (VCC2) has a wide range from 4.5V to 36V, which has made L293D a best choice for DC motor driver.

    As you can see in the circuit, three pins are needed for interfacing a DC motor (A, B, Enable). If you want to control speed enable pin is connetcted to the PWM pin of microcontroller . I have connected only one motor and  used the enable pin to contol the speed of dc motor.
abasit35 days ago

hello sir.....

this motor has variable speed . if i want to drive in clockwise as well as anticlockwise what the code of this operation????

also L293d this ic can drive two motors at a time,so if i connect two motors , do both motors rotate at the same time?????

sunil93 (author)  abasit34 days ago

For changing the direction of the motor you simple need to change the inputs A B of L293D

yeah you can connect the two motors but to make it rotate you need to connect the AB inputs and Enable2 inputs of second motor. study L293D and all your doubts will be cleared.

carlos66ba10 months ago
This is an interesting circuit and well made instructable. Note that what you are controlling is the power, not speed, however. For a future development consider adding a feedback loop that measures actually controls the speed.
sunil93 (author)  carlos66ba10 months ago
thanx man........yeah you are right by varying PWM power is controlled