Need advice building an animatronic eye

Let's Make Robots Beginners
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Hello: I’m new here so I hope I am in the right spot. I’m putting together an animatronic eye using Will Copley’s design: Notion – The all-in-one workspace for your notes, tasks, wikis, and databases.

This build uses Arduino Uno and a servo driver. In his tutorial, he shows a USB printer cable attached to the UNO. This is used to upload code of course but it is also used to power the UNO. The servo board used a separate 5V power supply. While using a printer USB cable works for setting this up, I do not want to use it normally. Also, I don’t understand why 2 power supplies are needed? So, I plugged in a 12V power supply into the UNO and routed 5V from the UNO power pins to the servo board. Now only about half of the 6 servos work. I then put the power back to the separate 5V supply and now nothing works.

I don’t understand why this does not work? The servo motor takes 5V, I confirmed that the UNO 5V pin is actually 5V. The UNO board can use a 12V power supply. I looked it up! I tried re-uploading the code with no luck. I rechecked the wiring as well.

What am I missing here? I ordered a new Arduino UNA and a servo board but don’t want to blow them up too (if that’s what I did).

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Use a separate, adequate 5V power supply for the servo board. The power supply must be capable of supplying at least 2-3A or more depending on your servos’ requirements.

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Thank you for getting back to me. So, if I understand you correctly, I need to use 2 power supplies, 1 for the servo board and one for the UNO. Is that correct?
Also, should the power supply for the UNO also be 5V or should 12 V work ?

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@BillR94 This might help regarding power:

If the robot is to be connected to the mains, it’s really up to you if you want one main power supply from the wall, which is then split to provide nominal voltages to each, or two power supplies from the wall. As soon as you start considering three or more, you really need to optimize the system. Hope this helps.

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