Bad USB-cable preventing SG-90 servo from working?

I have a strange problem here, which seems to be caused by using a bad quality USB-cable.

When using this cable with an original Arduino Uno, all is working well. I can upload sketches, Blink is working fine, all great. As soon as I connect a SG-90 servo to the Arduino, the communication between the Arduino and the PC stops, I'm unable to upload any sketches and the Sweep-sketch doesn't make the servo sweep, but just move a really tiny bit every second or so.

If I reconnect the Arduino with another cable, all is working fine.

The bad cable is new, unused and undamaged. I ordered several of these cables from eBay, and all of them have the same problem.
When I check them with a multi meter it gives 4.93 volt and about 12.4 DCA (when set to '200m', not really sure how to interpret this value).
The working cable gives also 4.93 volt, but 16.8 DCA.

Is this problem caused by the cable 'giving' not enough current, or is something else happening?

Hi,

When I check them with a multi meter it gives 4.93 volt and about 12.4 DCA (when set to '200m', not really sure how to interpret this value).
The working cable gives also 4.93 volt, but 16.8 DCA.

The 12.4 and 16.8 on the 200mA range means 12.4mA and 16.8mA, but you haven't measured with the servo running/working.

You will find the current will be much higher and the voltage at the arduino end lower.

Your dodgy cables are probably made with very light gauge wire.
Does the dodgy cable feel more flexible.

You really should be powering your servo off a separate power pack, the PC and the arduino controller is not made to supply the higher currents need by the servo when it begins to operate.

Tom... :slight_smile:

You must never power a servo from a USB supply, you will not get enough current
and you may risk damaging the computer whose USB socket you are using.

Use a separate 5 or 6V supply capable of at least 1A per servo. Don't use the Arduino 5V.