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[on:]

We are working on a project involving servos, which will require the use of a power supply. As mentioned in tutorials on this site, the Arduino ground and power supply ground need to be tied together. What kind of protection can we put in the circuit to ensure that current doesn't backflow through the Arduino in the event of irregular (or even normal) function. We were thinking of something along the lines of a diode or a transistor to only allow one way current flow. Any suggestions?

[Reply #1 on:]

Tying together a common ground connection between two different DC voltage sources is required in most systems to function correctly, but that in itself does not lend to any kind of 'back feeding' vulnerability. Sometimes there can be problems if it's possible that one voltage source can be on and the other off, so it's best if both power source be controlled with the same main power switch, or by other interlocking methods. Specific recommendations require specific system information.

Perhaps if you could post a schematic drawing of the complete system and power sources we could see what might be of concern to you, or have potential problems.

Lefty

[Reply #2 on:]

Attached is a crude schematic, but essentially is what the final design will look like. The power supply we used is this one: http://www.newegg.com/Product/Product.aspx?Item=N82E16817170017. Any help would be appreciated!

[Reply #3 on:]

Well, unless you manage to reverse the +12 & Gnd, I don't see where'd you have issues. Just be careful not to put 12V on an arduino input/output pin, that would be bad (catastrophic).

Where does the arduino get its power from?

[Reply #4 on:]

The Arduino is powered via USB.

[Reply #5 on:]

What you have looks perfectly OK, with power for the Arduino coming via the USB.  However, why not also connect your +12 volt supply into the Arduino power system and let the Arduino self-select between USB or main power.

From a colour semantics point of view I'd suggest you do not use red for the ground connections.  Red to me (and no doubt a few others) suggest a positive voltage (such as +12v).  I'd also suggest black for the ground connection.

jack

[Reply #6 on:]

Is there an advantage to powering the Arduino with the +12V supply rather than just sticking with USB? Also, I agree that my color selection wasn't the best. These settings were default and I just wanted a quick schematic for feedback. I didn't realize the color scheme would throw people off. 

Thanks for the input!

[Reply #7 on:]

Which servos are you using?
Not all hobby servos can handle 12v.  Most of mine let the magic smoke out at that voltage.
Many of the newer ones can handle it though.

[Reply #8 on:]

They are a few different ones:

http://www.servocity.com/html/hs-422_super_sport_.html

http://www.servocity.com/html/hs-485hb_servo.html

http://www.servocity.com/html/hs-645mg_ultra_torque.html

http://www.servocity.com/html/hs-85bb__mighty_micro.html

Thanks!

[Reply #9 on:]

Which servos are you using?
Not all hobby servos can handle 12v.  Most of mine let the magic smoke out at that voltage.
Many of the newer ones can handle it though.

Can you give us a link to some of those 'newer ones' that can handle +12vdc?

Lefty

[Reply #10 on:]

What you have looks perfectly OK, with power for the Arduino coming via the USB.  However, why not also connect your +12 volt supply into the Arduino power system and let the Arduino self-select between USB or main power.

.

That's not a great idea - the 12V supply to the servos will be very noisy.  If you do this you want another level of voltage regulation (such as a 10V regulator and decoupling) between the "raw" power and Arduino's Vin.

Also the 12V supply may be crowbarred on overload and reset the Arduino...  In general separate supplies for logic and big motors is a good idea.  If the maximum stall current for all the servos exceeds the power supply's rating, I would strongly suggest keeping supplies separate.

Actually looking at the PSU you select it seems to be a computer supply, not one designed for inductive loads...  I would add generous decoupling.

[Reply #11 on:]

Can you explain what you mean by adding "generous decoupling"?

[Reply #12 on:]

Aren't all your servos 6V rather than 12V?

[Reply #13 on:]

Aren't all your servos 6V rather than 12V?

As far as I know, except for possibly a few specialty item servos, 99% of typical R/C servos require 4.8 to 6vdc power.

Lefty

[Reply #14 on:]

The keyword is optocoupler.