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Topic: Powering three servos and Uno from one source (Read 1 time) previous topic - next topic


This is my first Arduino project, and I'm trying to take in as much as I can from the forums before posting, but there's quite a bit out there that's confusing!

So, I've read a lot of posts where people suggest powering multiple servos and an Arduino from an external power supply. I'm all about that, but in seeing the diagrams in most of these posts, I don't get how the power goes to the Arduino. Nonetheless, I have been looking around a lot, and want to make sure I'm figuring things out right.

First, the specifics. I have an Uno and three FS90 9g micro servos. The servos will be pushing a very light load, and have an operating voltage of "4.8-6V" according to spec. I don't know what the peak load is, but I don't anticipate coming close to hitting stall. I also plan on having one servo move at a time, though if the way I'm planning on wiring it can handle it, I would love to move two or all three at once. I anticipate moving one servo a couple of degrees every 5-10 minutes, and the other two will move up to 90 degrees on a 8-12 hour schedule.

My plan for wiring everything is to split the power source positive with one end going into the VIN pin of the Arduino. The other end would go into a 1N4001 diode and then split to the three servos. Connect all the grounds together and set individual servo controls on Arduino pins (say, 5, 6, & 7).

Does this wiring sound smart?
And if so, does it seem a 9V battery can handle this?
Or would it be easier to use a wall wart?


A 9V battery can handle a smoke alarm or a multimeter and that's the ONLY thing you should consider using them for. They're garbage
as far as every thing else goes. Forget you ever considered that idea and move on. Find something else. A 9V battery would probably power the arduino and three servos for a few hours at best. The servos don't draw much and a 9V battery could handle it but a single diode drop is only 0.7V . You would need a minimum of 4 diodes in series to drop 9V down to 6V and it MUST be 6V or less.


Or would it be easier to use a wall wart?

A 9v or 12v wall wart with a 7805 regulator chip like below makes for a simple power setup.

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I don't know what the peak load is, but I don't anticipate coming close to hitting stall.
In fact, every time a motor starts up, it momentarily draws the stall current. If you rapidly reverse direction, it momentarily draws TWICE the stall current. This includes the motor in a typical servo. You really need to know what the stall current is and plan your power supply accordingly, otherwise the Arduino may reset itself every time a servo starts to move.

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