Go Down

Topic: Best way to insure fool-proof control of a powerful servo? (Read 1 time) previous topic - next topic


Jul 12, 2011, 02:18 am Last Edit: Jul 12, 2011, 02:25 am by levorto Reason: 1
Hello everyone

This will be my first project on an Arduino, so bear with me if I am asking questions that might have already been answered.

I have been researching the most fool-proof setup for controlling a powerful servo, and I think I have come up with the best solution.
My means are limited in sense of funding, so investing in a motor board should be my last resort - e.g. if this does not work.

My setup will be: Arduino Uno (w/5V AC/DC) connected to a 5V 800mA(!) servo - which has its own power source (5V 1A - AC/DC).

Here is my question:

Would the following schematic provide fool-proof control of a 5V/800mA servo?
- and if yes, how can it be optimized to perfection?  :)

I have created this schematic based on how I de-ciphered comments around the web.

Looking forward to hearing if I'm on the right track :)


That circuit won't work as the "pulse" signal will be floating whether the transistor is on or off.

How do you define "foolproof"? Do you just want to protect the Arduino pin?


Rob Gray aka the GRAYnomad www.robgray.com


You show both the emitter and the collector leads of the transistor wired to ground. How could that possibly work? Why the transistor and diode in the first place? They serve no required purpose, even if wired correctly.

Any typical R/C servo wires the same for a arduino, arduino output pin control signal to servo control signal input pin, arduino ground pin to servo ground pin, servo ground pin to external power (4.8 to 6.0vdc) source, servo ground to external power source negative terminal.



Jul 12, 2011, 03:05 am Last Edit: Jul 12, 2011, 03:13 am by levorto Reason: 1
I am just trying to protect the Arduino board.

I had the idea that powerful servos had the same risk as gear reduction motors.
Hence the one-way diode. And thought the signal had to be strong, hence the transistor.

So there is no need for extra security when using a servo?

Just Arduino PIN to servo pulse,
Arduino GND to servo GND ,
servo positive to powersource positive,
servo GND to powersource GND,
and powersource GND to Arduino GND.

The website that made me confused: http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads

Might as well explain what I am going to use this servo for:
A Combined 12xKeypad & RFID Door Unlocker - possibly with automatic opening.


This is not a high-current load though, despite it being a "powerful" servo it still has a logic-level input. Somewhere inside you would probably find some amplification but you shouldn't have to worry about it.

Your circuit description sounds right.

Rob Gray aka the GRAYnomad www.robgray.com


Just to clear things up. Did I miss anything? No resistors or anything? Just making sure :)


levorto, that circuit should be fine for driving your servo.


Your servo will be stronger if you power it with 6v instead of 5v.
Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0


Your servo will be stronger if you power it with 6v instead of 5v.

Check that you do not exceed the maximum voltage rating of your servo. Some servos are not designed to operate on 6v.


levorto, that circuit should be fine for driving your servo.

Thanks :) - What a great and helpful forum! I am looking very much forward to inventing with you guys  :)

Your servo will be stronger if you power it with 6v instead of 5v.

Im not worried about the strength of my servo... Let's just say I have that part taken care of :)
http://www.servocity.com/html/hs-805bb_mega_power.html = 25 kgcm at max :P - I will let it run at 5V to reduce wear&tear.

Go Up