Discussion in "8051 Discussion Forum" started by    superman    Mar 13, 2010.
Sat Mar 13 2010, 06:59 PM

I have selected this project : Controlling a toy car (made with AT89C51 + 2 DC Motors driven by drivers L293D) from a PC wirelessly. (using RF)

I interfaced one AT89C51 to the PC through the COM PORT(RS232) which receives serial input as commands. With respect to the inputs I transmit a particular information through the TWS434 and receive it using the RWS434 (Transmitter and receiver ICs)

The received information is then given as input to the Port P1 of another AT89C51 which gives input to the Motor driver IC (Dual-H bridge) L293D through the Port P2. I have connected the 2 motors to output ports of L293D.

Whatever data that I wish to transmit is being transmitted and also received. The data also gets output from the Port P2 of the Receiver side AT89C51 (verified it through a Digital Mulitmeter)
The problem I am encountering is that, the motor doesn't rotate properly, it just rotates too slowly (less than 6 rpm - Note that the motor(12V DC) when directly conntcted to the power supply rotates at its mentioned speed of 40 rpm).
I found that if I remove the L293D driver IC from its socket and insert it back(while it is still powered on), the motor rotates properly until it is made to rotate in the opposite direction (by giving suitable values). I also found that whenever I try to measure the output voltage at the motor's end when it is rotating slowly through a Digital Multimeter the motor starts to rotate properly until its made to change direction.

So I thought L293D should be the problem and I switched to L298 driver IC.
Here the problem I am seeing is that I get Voltage of 12V from the out terminal of the L298 (across pins OUT1 and OUT2) but the motor does not rotate.

The following image gives you an idea of the L298 problem :
This does not work even though there is output voltage

But if modified like this it works (but obviously only in one direction )

Kindly help me out in this regard.
Both the L293D and L298 oriblems.


Sat Mar 13 2010, 08:21 PM
Well this may not be best answer but i think with 1st controller when motor rotates slowly that ic's VSS and VS is connected to positive Logic 5V not with battery connect battery there and give it a try
Sat Mar 13 2010, 08:59 PM
You should have 100nF capacitors on Vcc and Vs.

I would also add larger capacitors in addition to the 100nF.

[ Edited Sat Mar 13 2010, 09:00 PM ]
Sun Mar 14 2010, 12:03 PM
also check if your power supply is enough to provide sufficient current to motors.
Sun Mar 14 2010, 12:03 PM
[Topic moved to 8051 Discussion forum]
Sun Mar 14 2010, 01:32 PM
Thanks for the replies guys..
I found out the problem associated with the L293D.. it was a driver problem!!
Bought another IC and its working fine!!
thanks for your help guys..

But I'm still wondering as to why it gives problems when using with the L298!! I tried changing IC but still the same.

@Ajay Bhargav : Checked the power supply, its about enough to run a motor..
@ExperimenterUK : No change sir.. Its still the same! :-(
@Afnan : Connected according to data sheet and still the same.. The motor rotates only when Out2 and Out4 are grounded! So no rotation in opposite direction
Sun Mar 14 2010, 02:25 PM
well all is well when ends well

do submit your project here.. its a good learning project.
Sun Mar 14 2010, 10:33 PM

Here the problem I am seeing is that I get Voltage of 12V from the out terminal of the L298 (across pins OUT1 and OUT2) but the motor does not rotate.

Are you sure you were getting 12V across pins OUT1 and OUT2
and *also* across the motor connections ?

Logically, the motor would turn, unless it is faulty.
Could there be a bad connection or dry soldered joint ?.

What model is the motor ?.
Does it rotate both ways if connected to a battery ?.

[ Edited Sun Mar 14 2010, 10:38 PM ]
Mon Jan 03 2011, 04:51 PM
hi everybody, i urgently the circuit diagram n code in c of this project.. plz present it here.
i would be thankful..
Mon Jan 03 2011, 04:58 PM
i mean i need it.. sorry for the mistake

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Fri Sep 29 2017, 02:45 AM
i am doing the same project on verilog please contact me [email protected]
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i am intending to interface sd card with STM32F4 and want to write a file in sd card using SPI protocol but using HAL only. Can anyone help me PLEASE!!!!
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Fri Aug 18 2017, 11:37 AM
hi @ angel patel i will attach a file i hope it will be helpfull for you
Mon Aug 14 2017, 09:57 PM
@ angel patel... just log in and post your problem
Mon Aug 14 2017, 01:45 PM
angel patel
hey any one help to make the led scrolling display
Sat Jul 29 2017, 07:09 AM
I see the code for step motor h l 298 to rotate 45 degree, but all delay time, if I want to input sensor to h the pulses to stepmotor
Thu Jul 27 2017, 12:05 PM
okay fine



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