L293D problems to PIC Controller

[Jent CWH]

Hi..
I'm currently buiding my first real microC project.
I'm trying to drive two DC motor by using PIC18F4550. I have testing some of my pic programming, they can be worked nicely for motor forward and reverse and stop.

One problem I am encountering is that for some reason whilst the motor is turning, some pins on the microcontroller turn high (especially for L293D_pin_2, 7, 10 15 to PIC) - even when these are unconnected! I am suspecting either the problem because I am not using any protection diodes at all (and the back emf some how freaks the microcontroller.)

Could this be the problem? If so where should I connect these diodes and what ratings should these have? - Aren't these diodes included in the l293d itself? Or could this problem solely be because the microcontroller is faulty?

Hope can get help because I am quite worried the driver might ruin my PIC. Thanks much!
;-)

 

[spiralbrain]

Yes the diodes are included in L293D and are sufficient for most applications, Are you driving the motors from the same power line as the microcontroller? If yes then perhaps the microcontroller is not getting a steady power source and causes it to misbehave. try using a filter capacitor in your power supply, a 0.1uF across the pic power line as close as possible to the controller helps.

 

[Jent CWH]

yes, same power line with the microcontroller by using adaptor. Can you show me the circuit connection of the filter capacitor in power supply?