Problem with ontrolling a DC motor (bidirectional) using AT89S52 and L293D

hi all,

I am controlling a DC motor (bidirectional) using AT89S52, I connected the output signal to the L293D. but not understand why when I ON the microcontroller circuit, the current is flowing through the motor even I havent ON the L293D circuit? (I can feel the electromagnet at the motor)I connected the pin 1 and 9 direct to the Vcc, as I just control the high and low pulse.

Re: L293D

I'm not an Atmel microcontroller expert, but here's what could be happening, if you Atmel were a PIC *.
- Most microcontrollers have tri-state digital I/O pins. The states are high, low and high-impedance (aka high-Z). When the microcontroller wakes up, the pins are usually in the high-Z state.
- Since pins are in the high-Z state, the microcontroller is not driving the L293D.
- Something else is driving the L293D. It could be, for example, a stray current on the board.

Would this be consistent with your observations?
What happens if physically remove the microcontroller and power up the circuit?

There's a Yahoo group, which has good discussions of the motor control hardware:
**broken link removed** OSMC stands for Open Source Motor Controller, which folks in this group have actually built to high standards.

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* I'm also making some assumptions about your procedure and schematic. It would help if you post your schematic of snippets from it.

L293D

Please post your circuit... how are your enable pins wired ?

Are you using a breadboard ?

Re: L293D

Stray voltages on the drive and enable pins could switch the bridge on. If the drive is not comming from the microcontroller, try to put a 10k or More pull down resistor on the control pins of the Bridge Module.