newbie with uno r3

Development Tools IDE 1.x
1

i am a newbie to this stuff and after planning to build a robotic arm with servos i bought an arduino, i have done the basic sketches i.e. the sweep and knob using a potentionmeter and all works well when connected to the pc with usb but once i try with a seperate supply unit(9v ac to dc charger 150mA) and without the usb connected the servos no longer move instead they twitch slightly which also goes in rythm with the pwm port 13 micro led (the control wire to the servo is in port 3), the same thing also happens if i use without a potentiometer, is probably a simple answer sorry for my stupidity.

also another problem is after ive uploaded a sketch to the uno a few times it will say com3 port is already in use and then it cant be found in the serial port in tools, i have to then unplug the usb and close the program and replug and re-open it for it to re discovour com3

help is greatly appreciated!

2

"seperate supply unit(9v ac)"

Need a DC supply, not AC.

3

I think he used AC to DC adaptor , so it is DC not AC.
I think what he ask:
Why it does not work well when he used external power supply but it works when he used USB power supply.
:smiley:

4

Are you sure it is a 150mA supply? That may not provide enough current to run your Arduino and the motors.

5

If the ac to dc power supply onøy can give you 150mA, that is thebproblem. An usb 2.0 can give out 500mA and a usb3.0 can give out 1000mA.

So your problem mit be the power supply.

6

thanks alot guys i tried with a 9v battery and it works fine i looked around on a few other websites they also recommend ateast 500mA

7

I hate to be the bearer of bad news, but that 9v battery (small rectangular style) really isn't much better. It has very low current capacity and will only an hour at best.