L293d one power source

Discussion in 'General Electronics Chat' started by helloeveryone, Apr 5, 2015.

  1. helloeveryone

    Thread Starter Active Member

    Apr 8, 2011
    51
    0
    Hello everyone, I would like to connect a micro controller to a small dc electric motor using a l293d chip. I see that Vss is where I would connect 5V and Vs is where I would connect an external power source for example a 9V battery. If I'm powering my micro controller using a dc power adapter which can output a maximum of 1 amp, can I power Vss from the same power source or must I have a separate power source for Vs?

    [​IMG]
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    If the motors will run on +5V you can use a single source. You want to be careful to route the motor ground and the logic ground in such a way that they intersect at a single point. Using this method minimizes the interactions of the motor and the logic. You would do the same thing if you had two power sources instead of one. Are you planning to make a PCB or is this going to be a breadboard?
     
  3. helloeveryone

    Thread Starter Active Member

    Apr 8, 2011
    51
    0
    Yes, I had a feeling that I would have to be careful with the grounds. How can I be sure that the grounds are meeting at a single point?

    I'm using an ordinary mb102 breadboard and a MB102 Breadboard Power Supply Module. Would the grounds be alright if I connected them all to the same ground rail on my breadboard?
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    Generally no.
    You should run a separate ground wire from the L293 ground pins directly back to the supply common and a separate power wire from the Vs pin to the power supply positive terminal.
     
  5. helloeveryone

    Thread Starter Active Member

    Apr 8, 2011
    51
    0
    Is this what you meant? L293D.JPG

    This is the power module: http://img.dxcdn.com/productimages/sku_149664_1.jpg
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    What you want is two physical ground rails, perpendicular if possible, meeting at a single point. The logic and processor go to one of them, and the motor stuff goes to the other one.
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    Basically. Ideally the two power rails and common rails should connect together as close to the power supply source as possible to minimize any wire resistance.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    A caution about the '293. The Voh and Vol make this chip useless at Vcc2=5V. Hell, it is very poor even when Vcc2=12V. Ask me How I know.

    (I get only ~9V across my motor when running off 12V)

    293.gif
     
  9. helloeveryone

    Thread Starter Active Member

    Apr 8, 2011
    51
    0
    So the left ground rail will have two grounds from the l293d(or 4 if I connect 2 motors), and one ground from the micro controller. The right ground rail will have one ground from the power source, a battery or power adapter. Then I connect a jumper wire from one negative rail to the other. Other than wire resistance, does it matter at which end of the breadboard I place that jumper wire? Should it be right next to the breadboard power supply or at the opposite end?
     
  10. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    The connection between the separate grounds should be as close to the power supply as possible. The idea is to force noise on the motor ground to travel all the way back to the supply and then all the way out to the logic chip to affect it. It would help if you labeled your drawing with LOGIC_GND and MOTOR_GND instead of LEFT and RIGHT.

    If you run the grounds close together and PARALLEL, then noise will couple from one to the other. It would be better to separate them by some distance, or better yet make them perpendicular.
     
    Last edited: Apr 7, 2015
  11. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    Yes, you can connect.
    there is l298 also for higher rating!
     
Loading...