How to drive FS90 9g Servo with seeduino?

Other Hardware Motors, Mechanics, Power and CNC
1

Hi, I would like to control an FS90 9g mini servo using a seeduino.

I am given to understand that the Seeduino only supports 2.5 mA. Evidently it can support a max of 10mA if you set the Output Driver Strength bit (DRVSTR) to 1 for a specific pin.

I believe the 9g servo pulls a maximum (stall) current of 700 mA at 4.8V.

Can I split my battery leads so that it branches and goes to the Seeduino and the servo motor, so that the servo will pull directly from the battery? Or is there some other way I should power the servo motor?

Thanks,

2

Power the servo separately from the Seeeduino, but connect all the grounds (servo battery negative is "ground"). Servos inject electrical noise and high voltage spikes into the power supply, which can damage or reset the Arduino.

3

Thanks for the reply. Sorry, I am very new to electronics so I will ask for some clarification, if I may:

My device is going to be run from 3 AAA batteries (4.5V).

So I would branch the positive lead from the battery pack to go to the Seeduino and also the servo, but if the negative lead is branched the same way will they not be connected (at the battery)?

Like this:

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So all the power leads and ground leads are connected (at the battery)?

Thanks!

4

It is a bad idea to run a servo and a microprocessor from the same power supply.

Save yourself from buying another Seeeduino by running it from the USB port (or separate battery pack), and power the servo using a 4xAA battery pack. The servo won't work well or for long from a 3xAAA battery pack.

Connect battery negative to the Seeeduino ground.

5

This is a stand-alone device so running off the USB port is not an option (at least, not running it from a PC or something).

So it sounds like I need a separate battery pack for the microprocessor and the servo. That's a bummer. I don't have a lot of room in this device.

Instead of a separate battery, is there some kind of electrical filter device I could put between the battery pack and the servo to isolate it?

The servo pulls 100 mA at 4.8 V no-load. A AAA battery holds about 1000 mAh. So I have about 3000 maH of storage with 3 AAA batteries. That gives about 30 hours of use. 8 hours would be the minimum requirement.

This is plenty for this device in between chargings or replacement of the batteries.

6

I have been reading on how to isolate high-load servos from the microcontroller and found this:

Looks like they are saying you can split the voltage source (battery) as a way to do this. I'll have to build a prototype and see how noisy it is.

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7

It briefly draws the start/stall current of 650 +/- 80 mA every time it starts moving.

Instead of a separate battery, is there some kind of electrical filter device I could put between the battery pack and the servo to isolate it?

Yes, of course. Search for "power supply decoupling". This is an essential design skill for engineers.

Good luck with your project.

8

I am building a toy where the servo will activate once or maybe twice during an 8-hour play period. Basically the toy waits for input and then triggers the servo briefly (think a Jack In The Box). The toy will use a single sensor that draws 150 mA. The Seeduino itself seems to draw less than 15 mA. I also have a speaker that will make a noise but it will only beep once or twice in a play session like the servo.

So while sitting and waiting this device will consume less than 200 mA. So it should run about 15 hours on a set of three 1000 mAh battereis. This is acceptable.

Thanks for your help!

9

The expected battery lifetime will be about 5 hours at best.

Battery capacities add when batteries are wired in parallel, but not when wired in series.

10

Thanks for that term - I have found a helpful article:

https://learn.sparkfun.com/tutorials/capacitors/application-examples

Doh! I should have known that one from when I added batteries to my RV!

Also, I found a similar question you had responded to on isolating servos here that is helpful:

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