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driving motors 12V/580mA through Boe-Bot — Parallax Forums

driving motors 12V/580mA through Boe-Bot

thomas_pittinthomas_pittin Posts: 29
edited 2014-04-24 11:15 in General Discussion
Hi,

I have a problem with my boe-bot
I want to drive two motors (12V 580mA) through my boe-bot, i tried with L293D but don't work perfectly

anyone can help me?

Thanks
Thomas

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2014-04-24 09:35
    The chip is rated at 600mA per channel. Although you are right on the edge of that ( 580mA ) you should have been ok. Can you explain what didn't work, and perhaps provide a schematic and code that you were using?
  • thomas_pittinthomas_pittin Posts: 29
    edited 2014-04-24 09:46
    The motors must be driven at 12V and I drive it at 4V so the code and the schematics are OK, but I don't have power in it...Can I drive the L293D at 12V or 9V?
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2014-04-24 09:58
    The datasheet for the L293D claims 36V. Still a schematic and code would help.

    Reference:
    http://www.ti.com/lit/ds/symlink/l293d.pdf
  • thomas_pittinthomas_pittin Posts: 29
    edited 2014-04-24 10:14
    L293D connection.png


    Now the VS+ and the VS+ ENABLE is the same voltage(5V), I try to connect the VS+ to 12V, but the ground of the 12Vbattery is the same of my Boe-Bot?
    L293D connection.png
    960 x 540 - 10K
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2014-04-24 10:29
    Is the VS not split into two separate supplies on the Boe-Bot? If so, then you will need to place the L293D on a separate bread board and wire it up yourself.

    Referring to the BLOCK DIAGRAM on page 2 of the PDF, Pin 16 (Vcc1) goes to your 5V supply and Pin 8 (Vcc2) goes to your 12V supply. The inputs (2,7,10,15) should all accept 5V logic. The enables (1 and 9) should also accept 5V logic. The grounds (4,5,12, and 13) are COMMON between Vcc1 and Vcc2.

    For best results:

    - Use the Enable lines to control speed via PWM.

    - When changing direction, don't just flip the input from HIGH to LOW or vise versa. You should transition through the Enable line to prevent "shoot through" by disabling the output. i.e. The input on pin 2 is HIGH and the input on pin 7 is LOW while the Enable on pin 1 is HIGH ... Instead of making Pin2 LOW and Pin 7 HIGH ...First make the Enable on Pin 1 LOW, then make Pin2 LOW and Pin 7 HIGH before you resume the Enable pin to a HIGH






    Reference L293D PDF:
    http://www.ti.com/lit/ds/symlink/l293d.pdf
  • thomas_pittinthomas_pittin Posts: 29
    edited 2014-04-24 11:09
    Could you please explain me how can I use the PWM on ENABLE Pin?
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2014-04-24 11:15
    Sorry, I miss spoke... the PWM command for the Basic Stamp is not really ideal for generating PWM to drive a motor. It's too fast, causing the drive transistors to over heat. (<-- They spend too much time in their linear region)
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