is this a issue with my dc supply?

I'm newbie to electronic circuit. got a weird issue and have no idea why it happens.

I can drive a sg90 servo motor by a USB connected 5v power source with no problem. but when I connect the servo motor to my new bought DC supply, it just doesn't work!

I'm pretty sure I've set the right voltage (5V with limit to 6V). The only time point I can make the motor work is by connect/disconnect the power source from the dc supply. I can't drive the motor by the PWM signal sent from my esp8266.(it did work when i'm using USB power).

i can't think of a reason why... thx in advance!

do you have the servo, power supply and Arduino grounds all connected?

wg0z:
do you have the servo, power supply and Arduino grounds all connected?

i connect the servo GND connected to - to my dc power supply and servo 5V to my + of my dc power supply. esp8266 use a usb power source which is separate from the motor's power supply.

Connect the ground of your power supply to both the servo ground and the ground of the EPS8266.

Grumpy_Mike:
Connect the ground of your power supply to both the servo ground and the ground of the EPS8266.

the thing is that I don't have a GND port on my PSU.

I think you need to post a connection diagram and more details or links to what you are using.

Photograph of your assembly.

Photograph of a hand drawn circuit diagram is fine , do not waste time with fritzing software.

jjloki:
the thing is that I don't have a GND port on my PSU.

Use the minus.

esp8266 use a usb power source which is separate from the motor's power supply.

Which is why it won't work.
Read this:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

ChrisTenone:
Use the minus.

Thanks for the reply!

Grumpy_Mike:
Which is why it won't work.
Read this:-
Power Supplies

Grumpy_Mike:
Which is why it won't work.
Read this:-
Power Supplies

Thanks a lot for the reply. I think that's why! but I still don't understand why the usb source to the servo can work while the DC supply power source doesn't work?

jjloki:
Thanks a lot for the reply. I think that's why! but I still don't understand why the usb source to the servo can work while the DC supply power source doesn't work?

Because it is an incomplete circuit. You might have + and gnd from the power supply going to the servo, completing that circle (circuit), but you only have + from the arduino, no gnd, which is an incomplete circuit. Power MUST return from whence it came. Sorry, it just sounded like a Hobbit thing.

tinman13kup:
Because it is an incomplete circuit. You might have + and gnd from the power supply going to the servo, completing that circle (circuit), but you only have + from the arduino, no gnd, which is an incomplete circuit. Power MUST return from whence it came. Sorry, it just sounded like a Hobbit thing.

I've tried again, now it works! Thanks a lot!

jjloki:
Thanks a lot for the reply. I think that's why! but I still don't understand why the usb source to the servo can work while the DC supply power source doesn't work?

Because the USB is powering the Arduino and so has the ground joined up to everything by default. Once you add an extra supply you have to do the wiring of the servo ground - power supply ground - Arduino ground.