View Full Version : Driving motors through L293D

11-16-2005, 03:16 PM
Hi ,

I m building a robot for my end sem project, I m almost done with the circuit part.
Now m facing a problem with the power supply,
My robot was working fine with the transistorised power supply .But when I try it with the batteries using a 5 volt regulator chip (7805).It stops working .
Even with the adaptor it doesn’t work.

I m using L293D to drive my motors(2 in no.) ,in both direction .Normal current required by the circuit is bout 330 mA .and when it switch to reverse direction current shoots up to 560 mA .

I had tried using 9 volt batteries, n up to 10 volt from adaptor, but no output .Could anyone suggest me a way to get rid of this problem.

11-16-2005, 11:30 PM
maybe the 7805 is not sourcing enough current..

and are you sure withh all your l293D connections?? specially the Vm and Vcc pins??

what is the voltage specs of your motor??


11-17-2005, 04:10 AM
use separate power supply for L293D and motor

there are two pins on L293D pin 16 u give the logic 5V supply and i think pin 8 the supply for motor

11-17-2005, 01:20 PM
What is the current\volatge rating of your battery? 7805 can source enough current to drive your motor.....remember there is a drop to 2v across it.

11-18-2005, 07:26 AM
Post your circuit diagram.

If your sure your 5V is giving out what it's intended to,
check these

VCC1-> 5V
VCC-2->9Volts or whatever supply you want to run your motors
GND1,2,3,4 -> all Gnd
Check if 1A,2A,3A,4A are receivin proper logic voltages.

Once agian,post your circuit.

11-18-2005, 11:44 PM
thank u all for ur suggestions . specially yogi , ur idea worked , i tried it wid diff power supply , now its workin .
thank u once again ... :)

but now m facin problem wid the logical part

my circuit diagram is this (ignore the reciecver part i had rectified mistakes in it)http://students.iiit.ac.in/~ankit_garg/ckt.JPG

my robo works quit fine when in air , but ,when i keep it on floor , it start showin weird actions . all in all dont work properly ,

my voltage specs are - 6 (i.e. 4 - AA size batteries) volt to L293D

n 5 volt (6v I/P to 7805 ) to rest of the ckt

all in all 8 AA batteries m using ...

11-19-2005, 11:00 PM
but now m facin problem wid the logical part

Whats the problem...if your robo can work fine in air??

my robo works quit fine when in air , but ,when i keep it on floor , it start showin weird actions . all in all dont work properly

Probably...your motor can't drive that much of load!!

n 5 volt (6v I/P to 7805 ) to rest of the ckt

Did you read what I said above...for 7805 to provide voltage regulation....input should be atleast 2volt high...i.e.7volts(atleast)

And regarding your emitter circuit.....there is no need to put those redundant AND and 2N2222,as it can be made to work it.

11-19-2005, 11:36 PM

i got da solution of my , problem , actually a wire wasn't soldered properly , so when in air it woks a it was in contact , but at floor because of pressure it deteches n stops workin ,

thanks neways :)

11-20-2005, 03:36 PM
hii there ,

after solvin previous problems , now m facin a new problem , n not able to fix it :cry: ,

actully , whts happinin is , my bot takes jerks ,while moving . i mean its logic is wokin pritty fine ,n sensors too . but then also , it is not showin xpected performance .
first i thoght it may be the things near it . but then in an open area , same problem presisit .

i m givin 12v power supply (8 AA batteries) to it . 12v to L293D n 5 v regulated to rest of the ckt .

11-20-2005, 05:50 PM
It would really help,if you post your L203d circuit

11-20-2005, 10:41 PM
hii ,

my ckt diagram is

desperately waiting fer ur reply !!!

11-21-2005, 01:56 AM
pin16 must be 5V or a max of 7V..see datasheet for the l293d

page 5 here

Your chip must be heating up.

L293d has a thermal shutdown function..either it will give all kind of crap signals when its heated up real bad ..or it will shutdown.

I'm thinking tht when you hold your machine up in "air",theres no load on the motors..
when you put ity on the ground ,it heats up and shuts down..

Before you do any changes,run your setup..see if your chips heating up.

That will narrow the problem..

Yea...on a lighter side..when nothing works in a circuit having chips..we engineers have a habit of touching the chips,to see if they heat up..gives us a little burn..but you dont want going and blowing chips around..(or if you have an expensive power supply,keep an eye on the current)

11-21-2005, 10:31 PM
hi there,

m still facin the same problem , its takin jerks again , i had tried it wid Giving 5 volts to the VCC1 of L293D still i m facing the same problem . And to my surprise was that when the Switching is taking place the regulator is giving the output of 3.46 volts , i think this may cause the problem , this much voltage will not be enough to drive the logic !!!
plz help!

11-21-2005, 10:38 PM
Try another L293d chip

11-22-2005, 12:56 AM

Are u using seprate power supplies for logic and the Bridge ??? ... This happened to me one though on uC ... Motors caused the supply voltage to drop and reset the uC - jerky motion .

Second thing check the Current / voltage before and after the motors are switched on ... Voltage drop should not be encountered .

Also what is the current rating of ur motors .

So -

Seprate power supplies
Check voltage current level ( in various scenarios )
Check the H-Bridge IC as Ice said .

11-22-2005, 10:26 PM
hiii ,

ya i did the change , as suggested by ice , n bout power supply , yes i m using same power supply for it , but when i trying it wid diff power supply didn't make make ne diff.

but i guess i had found the problem , may it is due to the long range of my tsop i guess it is sensin the objects which r not in my sceneario .

04-02-2006, 09:15 PM
im sandeep . im makin a maze solvin robot as my mini project.im usin astable mutivibrator as ir transmitter and tsop 1738 as ir reciever.the bot is 15cmx10cm in size.will der be any problems with reciever.

im usin 2 dc motors.i like to use relays instead of drivers.wats ur suggestion

04-02-2006, 10:16 PM
there usually isnt much problems with 555 but the pulses of a uC are much cleaner and accurate..

anyways. using relays or a driver is completely up to you.. I dont see the huge difference that would make in an analog circuit..


04-03-2006, 10:49 PM
Sandeep I dont know if that was a mistake.. but I guess you used the new topic button instead of post reply button and hence created a new topic..

Anyways.. no need for thanks.. this is a forum .. useless if there are no answers


04-19-2006, 08:10 PM
what wil be the output of ur ir reciever ,when it is recievin a coninuous 38kHz ir signal and when it recieves no signal, rockgrid

04-20-2006, 11:08 AM
A TSOP 1738 goes low when it detects 38KHz pulse and remains high otherwise


04-29-2006, 12:38 AM
im usin a simple astable multivibrator with an ir load and a tsop 1738 reciever for my robot.what shoul i do to control its range.the reciever ckt is same as the ckt of rockgrid.i want to sense objections from 2cm away[/img]

04-30-2006, 03:07 AM
Break a chopper-wheel Led sourcre/sensor module and use it as a "reflective sensor (you'll find 2 in an old mouse)

04-30-2006, 11:03 AM
plz explain it ,dosel

04-30-2006, 02:01 PM
Sorry That was for some other forum...
1. As I see it, you are making a uC less mouse. This needs a light/ no or less light sensor.Since you have a L298 You can attach a LDR/Preset combo to the I/P.
2. OR, the TSOP o/p can directly connect to the ip of 293.
3. OR this Ckt:

Shown is SPDT relay. You can change to DPDT.
2 ckts for 2 motors.

04-30-2006, 05:31 PM
im makin a maze solvin robot usin l293 driver,astable mv with ir diode as load and tsop as reciver.but the problem is that i want it to sense obstructions only from 2 or 3 cm away.i heard that its havin a range of a few metres.how should i reduce its range

04-30-2006, 11:46 PM
then dont use a TSOP!!
use a normal photodiode or LDR.. just increase the intensity of IR LED by putting higer resistance thats it.. it will even detect black as a surface..


05-01-2006, 10:23 AM
Absolutely rao.
TSOP is VERY sensitive. It almost responds omnidirectionally!
To decrease sensitivity ( ? ) you can enclose the entire module in black paper and put a tube of 3mm to 5mm inner dia and aim it at some convenient distance. This will make it directional and less sensitive ., ie. less distance.