I'm calibrating a single SG90 servo using an UNO board powered by USB cable.
But I've found that some cables aren't able to power the servo (board reboots when servo tried to move), while some other cables will work just fine.
The cables works completely fine to upload sketches, and works fine when used on my printer.
Visually the cables looks the same, the markings on the cables are:
doesn't work: 24AWG/1PR AND 24AWG/2C
works: 28AWG/1P AND 28AWG/2C
works: USB 2.0 high speed (cable very thin compared to the other two)
I'm confused as to why there's a difference?
and how do I differentiate the difference when I need to buy a new cable for the UNO?
On the board I have a sketch that rotates the servo to 0 then 90 and waits 10 seconds.
on the two working cables, they rotate just fine, will rotate back and forth multiple times.
on the other cable, it won't move, just keep rebooting.
Plugged into the same port on the same PC, only difference is the cable, so I came to the conclusion that it's the cable,
The worry when powering a servo from the Arduino 5V pin usually relates to the inability of the Uno to supply the required current. However, if the Uno is powered by USB rather than the barrel jack or RAW pin then is this really such a worry as the onboard voltage regulator is not involved ?
For sure there are other considerations such as can the USB connection supply enough current for the servo but the Uno has a PTC thermistor and MOSFET in series with it with the 5V supply and will shut down if too much current is drawn. This will not damage the Uno
What @testbugtai describes could be the USB power source and/or cable not being able to supply enough current, particularly through a long lead with thin wires, or the PTC/thermistor cutting off the supply if the current taken is too high but frankly, when I have done casual experiments with a single 9 gram servo I have always powered it from the 5V pin and have experienced no problems
Having said all that, the best thing to do is, of course, to power the servo from an external supply. 4 AA batteries makes a good power source and battery holders are easy to come by
Maybe, maybe not. There are many unknowns in OP post, for example missing schematics, missing code, we don’t even know if the UNO they are using is cheap CN knock off. The original UNO has a fuse that servo can blow up. Also USB source, what is it, what it’s specs? All we know it is a bad idea through OPs own admission yet we are here.
On the not working cable, it's slightly shorter and marked 24AWG, isn't that thicker than the working 28AWG?
Am I to assume the marking is false?
or 24AWG cable provides enough current so servers overdraw, whereas thinner cable provide less current so no over draw? (this seems sounds weird?)
