line follower doubt: pull up resistors

Thread Starter


Joined Mar 11, 2009
i am using a AT89S51 M.C i have heard of sumthing called pull up resistors......... wat exactly r these pull up resistors? wat r it's functions? how shld i connect them to the microcontroler???? and yes pls note that i am not using a H-BRIDGE. just d LM324 COMPARATOR AND L293D MOTOR DRIVER............
PLSSSSSS reply soon..........:)


Joined Jul 17, 2007
I am using an AT89S51 uC. I have heard of something called "pull up resistors" ......... what exactly are these "pull up resistors?"
Pull-up resistors provide a source of current. They are normally used in open-drain and open-collector circuits.

How should I connect them to the microcontroller?
Why don't you post a schematic diagram of what you have designed thus far, so that we might be able to determine whether or not they may be necessary?

And yes pls note that i am not using a H-BRIDGE; just an LM324 COMPARATOR AND L293D MOTOR DRIVER
The LM324 is not a comparator; it is an operational amplifier, also known as an "opamp" for short. Many comparators have open collector outputs; they require pull-up resistors.

The L293D is a 4-channel push-pull driver.

Before we can suggest a course of action, we need to see your schematic.