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I understand why servos and motors require an external power source when run from the Uno, but I've seen a lot of tutorials (for example, this one), where the servo is connected directly to the Arduino's 5V port. I did this, and I think it fried my servo. This is also the method shown on the official Arduino tutorials for Knob and Sweep. In fact, the knob tutorial was the first and last tutorial I tried with my servo -- after trying it, the servo didn't work.

It went like this:
1) Try sweep code without using external supply. Works fine.
2) Try knob code without using external supply. Servo hums without moving and heats up (a lot).

Why do tutorials say to do this if it's not advisable?

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    "I think it fried my servo". servo? not Arduino? – Juraj Mar 20 '18 at 8:40
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    The servo no longer works, but I’ve used the same Arduino to power other things, including other servos on a separate power supply (now that I know). – Jim421616 Mar 20 '18 at 8:43
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    Did it die immediately or work for a bit and then die? Is it possible that you got a bad servo? I've occasionally gotten one dead servo in the few batches I've ordered. – Adrian McCarthy Mar 20 '18 at 21:50
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    It went like this: 1) Try sweep code without using external supply. Works fine. 2) Try knob code without using external supply. Servo hums without moving and heats up (a lot). Hmm...I'll add that to the original question. – Jim421616 Mar 20 '18 at 21:51
  • Mhh, are you sure, that you connected everything correctly? I thought long about this and I see only 2 reasons, that it would heat up like this: 1. You have corrupt hardware or 2. You connected something wrong (like for example wrong polarity). Are you sure that everything is connected in the right way? – chrisl Mar 21 '18 at 9:25
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Most likely you fried the voltage regulator or the diode on your Arduino board (depending in which power source you used), because the servo has drawn too much current.

Many Arduino Kits or Starter Packs come with really small servos. These do not need much power (especially when no mechanical load is attached to them), so you can power them directly from the 5V pin. Greater/stronger Servos draw much more current and cannot be safely run in the 5V pin.

Many tutorials show this, because it is an easy start for a beginner. And with the right servo it works. More sophisticated cases are not covered there.

EDIT:

Since your Arduino works fine, the voltage regulator and/or the diode should be fine. I tested the Knob example on my Arduino Nano, while powering the servo on the Arduinos 5V pin (and the Arduino is powered over USB). When the Servo is moving, you can see that there is a significant power draw (The power LED gets a bit dimmer), but not so much, that it would be a problem for the Arduino or USB port. Also the example code works as it should, without the servo heating up. I also used a SG90 Micro Servo (9g, by Tower Pro; same as in the tutorial you linked). I also tried the same with an external power source (5V from a powerful USB charger). It still works as intended, but with more power, since the servo now can draw much more current to produce a higher thrust.

So the only thing, I can think of for your problem is, that you either have corrupt hardware, or you have connected it wrong (for example wrong polarity). My Servo has the same color coding for the wires as in the tutorial you linked. Brown is ground, Red is 5V Vcc and Yellow is for the pulse signal.

  • it’s a small SG90 hobby servo, came with the starter kit I bought. How can I test the voltage regulator and diode on the Arduino? – Jim421616 Mar 20 '18 at 8:42
  • @Jim421616 did you use an external power supply when powering the UNO and the servo? If the answer is no, then you haven't fried the regulator. If you did, attach it again and then measure if on the +5V pin you actually have 5V. if you haven't (the USB needs to be disconnected, only the power supply needs to be connected), then the onboard regulator is fried. If you have, try connecting the "fried" servo to the external power supply you have (it should be a 5V power supply). If it moves or becomes stiffer, it works, otherwse it doesn't – frarugi87 Mar 20 '18 at 10:54

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