L293 and Microcontroller

Discussion in 'Embedded Systems and Microcontrollers' started by bsfrye, Apr 2, 2009.

  1. bsfrye

    Thread Starter Member

    Feb 20, 2009
    I am using a ATTiny84 micocontroller to control a L293. When I put my volt meter to each of the output pins on the microcontroller the logic is perfect (it's all slow enough that I can measure it with the volt meter). As soon as the L293 gets plugged in - nothing works. One particular output of the controller drops low for 1 second when a button is pushed - yet there is always 5 volts on the pin when the L293 is plugged in. I am at a complete loss. I have pulled my PCB apart and installed it all on a breadboard and still ahve the same problem. Any ideas on what I can do to trouble shoot this? I assume the ATtin84 can control the L293 (10 ma per output pin, 40 peak but not recommended). Any ideas? I am at a complete loss.
  2. SgtWookie


    Jul 17, 2007
    Why don't you start by posting a schematic of how you have things wired up.
    Note that Vcc1/Vss (logic supply voltage; pin 16, pin 20 or pin 28 depending on the package you have) should be >=4.5v, but not more than your ATTiny's supply voltage.

    ST Microelectronics indicates that you can use 4.5v to 36v for the logic supply; I believe this is in error. Texas Instruments' L293D has a range of 4.5v to 7v for the logic supply.
    Last edited: Apr 2, 2009
  3. mik3

    Senior Member

    Feb 4, 2008
    Do you have a pull down resistor to ground on each of the outputs of the uC?