Recently I was trying to drive two motors with atmega328 and L293D motor driver IC. The power supply section is shown below
I used a 12V battery with high current driving capability.The motor was not connected but even the led blink doesn't work. I verified the circuit for hours. Then I connected a 9V battery with LOW current driving capability as input. This time everything was working properly. Finally I used a 100uF capacitor at the input with my 12V battery and it works!
[note:The motor was disconnected all the time. I checked the output with an LED]
Can anyone explain what happened. How does it work with that 9V battery?