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I have purchased an MG995 servo (4.8-7.2V operating voltage, 170MA no load operating current draw) and will power this using a 5V, 2A mains plug pack. Do I need a breadboard to connect this with my Arduino (which will itself be powered through its usb port)? Or is it possible to connect the servo with the Arduino directly?

If it's possible to connect it directly, which pins should I be using on the Arduino? Will it look something like this: Servo to a RedBoard

except the red wire (and black wire?) connects to the external power supply?

Any answers (or links to relevant tutorials which have all three of these components) would be welcome. Thanks!

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  • Don't pull the power for the servo through the Arduino. They need to be powered in parallel or from separate supplies. What you have drawn can burn up your Arduino.
    – Delta_G
    Nov 5, 2018 at 0:10
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    Be sure to connect the grounds.
    – Delta_G
    Nov 5, 2018 at 0:10
  • are you asking how a breadboard works?
    – jsotola
    Nov 5, 2018 at 3:31
  • Potentially - I haven't purchased a breadboard so if it's possible to connect the servo (powered externally by the plug pack) and the Arduino (powered by a USB cable) together without one that would be better. if possible ;D
    – Stacey1234
    Nov 5, 2018 at 3:44
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    From what I know, and what is said here, you connect the negative terminal of the power source to arduino ground, as well as the ground of the servo. Because both the power source, and the signal have to travel as 2 independent circuits.
    – Magnus Wootton
    Aug 30, 2021 at 9:51

2 Answers 2

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Your question is not very concise, but I'll try to hit the main points.

I'm going with the assumption that your "Arduino" is the Sparkfun Redboard. The Redboard has a current limit of <800mA (heat management on the Redboard probably lowers this number even more), as per the LM1117 voltage regulator listed in the provided RedBoard schematic, and a minimum input voltage of 7V. You won't be able to power your Arduino with the 5V2A powerbrick. If you are powering the RedBoard through the standard USB, then it will typically be limited to 500mA.

Are you sure your servo has a no-load draw of 170mA? That's really high for a servo. If it does, then I'm assuming it's a large servo that likely has a high stall current draw, so 800mA from the Redboard's on-board regulator won't cut it, nor a USB port.

To power your servo externally, wire the servo and Redboard according to the schematic below. The power supply is indicative of your 5V 2A "wall wart". It's important to note that you need to connect the ground of the the power supply to the ground of the Arduino. For controlling the servo, check out Adafruit's servo tutorial. You will also need to provide power to your Arduino via USB or a DC barrel jack with a power brick that outputs >= 7v.

enter image description here

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  • Would you please explain why it is necessary to connect the power supply ground to the arduino ground? Thank you.
    – bcsanches
    Jun 25, 2019 at 21:21
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    If you don't have the ground connected to the Arduino, there is no return path for current meaning your signal wire is useless. Also, in order to measure voltage you need a reference point. If you have no ground or reference, it has no idea what the voltage you are supplying it with is, or high that voltage point is with respect to ground is. So you tie both grounds so they both have the same reference point and to provide a return path of current for your control wire (granted it's an insanely tiny amount, nevertheless still must be there)
    – AJ_Smoothie
    Jun 26, 2019 at 17:21
  • I always thought that "ground" is "ground", so Arduino has its grounds connected to its own power supply, that whats confuses-me. Thanks
    – bcsanches
    Jun 28, 2019 at 13:02
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You did not indicate how you plan to connect the 5V, 2A mains plug pack to the Arduino board. If you want to use the barrel jack on the left, please note the listed input voltage. 5 volts is too low if you plan on powering the Uno board with the external power source. There is a voltage comparator circuit that will switch over to the barrel jack power if the voltage is high enough.

But since you are not really asking about powering the Uno, just the servo, then it gets interesting. The Sparkfun schematic shows a diode in line with the barrel connector and the Vin connection point on the board. This could provide a power path for the servo. The problem is that the servo voltage range 4.8 volts on the low end. With a 5 volt output of your external power supply, a voltage drop from the diode would give the servo almost enough voltage to meet the 4.8 volt minimum but not quite.

You are better off to not connect the servo power through the Uno board. If you had a somewhat higher voltage supply, at least 6 volts, then it would be ok. But if it is only 5 volts then it really is at a very marginal level.

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  • Hey, thanks so much for answering.I'm all pretty new at this so if I clarify what I meant I'm not sure if that will actually help (let me know!).So I want to power the Arduino board using a USB cable (from a laptop to the Arduino's usb jack). The servo I am using draws too high a current to power it using the 5V pin on the Arduino,so I have been advised to buy a plug pack (the 5V, 2A one),strip the end of the cable and connect it's wires to the servo (in order to power the servo separately from an external source) Basically my question is how do I connect the servo to the Arduino? Which pins?
    – Stacey1234
    Nov 5, 2018 at 3:23
  • arduino.cc/en/reference/servo
    – user33153
    Nov 5, 2018 at 14:04
  • You need to make sure what is the positive wire and what is the negative wire. You then connect the negative wire of the power supply to the Black wire of the servo above. The positive of the power supply connects to the Red wire. The Yellow and Black wire also connect to the Uno board as you show above.
    – Rudy
    Nov 6, 2018 at 4:35

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