curious battery problem

i used arduino to control one toy motor with L298N, the motor only want 3-5V voltage . I just have a AC/DC adaptor which can output 9v 1A ,So i used it to supply the arduino and L298N. because the motor is small ,i used a 78L05 to get 5v for L298n Pin4 and connect the adaptor output directly to arduino external powerin . but the arduino seem not to work and blink and the outpin (should high) have no result. After five or later minutes, it work and not blink. i think maybe the adaptor not provide enough current for arduino,but the adaptor output is 1A and 9v , is not enough to driver a small motor and arduino??

i used arduino to control one toy motor with L298N, the motor only want 3-5V voltage . I just have a AC/DC adaptor which can output 9v 1A ,So i used it to supply the arduino and L298N. because the motor is small ,i used a 78L05 to get 5v for L298n Pin4 and connect the adaptor output directly to arduino external powerin . but the arduino seem not to work and blink and the outpin (should high) have no result. After five or later minutes, it work and not blink. i think maybe the adaptor not provide enough current for arduino,but the adaptor output is 1A and 9v , is not enough to driver a small motor and arduino??

Check the specs on your motor. Those cheap low voltage motors take 2 amps easily. Your 1A power supply doesn’t come close.

Also, 298N has a minimum motor voltage of 5V (and up to 46V). It doesn’t play well with low voltage motors.

when i used USB supply for Arduino, It work well.I Want to know when arduino use external supply ,what is its working voltage and working current? if i use the usb power , i have two power source, it is nonsense. anybody can shed a light ?

If you mean the USB supply for Arduino and the 9V adaptor for the motors, what's happening to you makes sense. The motor is putting a huge load and a lot of noise on the power power supply. The supply can not keep a stable 9V at such a high current, so the voltage drops down. When it drops too far, it causes a brownout on the Arduino and the Arduino resets.

Even if you got a 2 amp supply, you'd probably have the same problem because of noise. You can try putting a decoupling capacitor across the power supply near the ATMEGA chip on the Arduino and maybe a second one across the power input to the Arduino board.

thanks ,oracle, do you mean i should put two capacitor, one across the two wires of motor and one for power supply between Arduino. in fact i have put one 104 capacitor across the two wires of motor,but it still not work . should i put anotor between power supply. i will try it. thanks again.