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How do I power an UNO and two servos with a wall wart? Answered

I have a project that I want to power with a wall wart (6v 2A). The project is a "Useless Machine", so it's not a complicated project. It uses 2 standard servos and one micro. I have searched a LOT, but I'm unable to find out how to properly do this because most projects use batteries. I know the motors and the UNO need to be powered separately. I thought I could simply splice and connect the 6 volts from the adapter to VIN, and also connect 6 volts to my servos, and tie the grounds together. And that worked for a little while. But then it quit working. Now I have >3 volts going to both my Arduino and my V+ line to servos unless I disconnect one. I honestly don't know which way to go at this point, so I'm reluctantly posting this question. I would appreciate any direction.

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Steve_Lane63 (author)2018-02-12

Randofo to the rescue again! So I can connect a 9V wall wart to a 7805 (with caps and heatsink), and power the arduino and servos from the same output?

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randofo (author)Steve_Lane632018-02-12

Yup. If you are just using two standard servos and an Arduino, I don't think its likely you will run into any current problems.

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randofo (author)2018-02-12

It's best not to use the V-in pin on the Arduino unless you first send the power through a 7805 voltage regulator. The V-in pin has no protection circuitry. This would require a power source with a higher voltage though (presumably 7V+).

You can use the Arduino's input power jack, but then your wall wart needs to also be greater than 7V. Of course, then you have the issue of powering the servos with 6V or less. The Arduino limits the amount of current it can provide on the 5V pin, which is frustrating...

Because of this, I might lean towards using a 7805 voltage regulator to power the Arduino through the V-in pin and provide power for the servos from the regulator as well. The regulator gives you a 1 amp max output, which is still better than using the Arduino 5V pin.

Alternately, you could get a high-current 5V wall wart that are typically sold for LED strips, and hope for the best. Or do that and add some over-voltage protection with a zener diode and/or add a 10uF electrolytic capacitor to keep the power source 'smooth.'

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steveastrouk (author)randofo2018-02-12

I thought the onboard reg was an LDO ?

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