Powering servo from Arduino Pro Mini 5v

Hey, new here.

Searched the net, the only relevant info I could find was a post on here dating back to 2009. http://arduino.cc/forum/index.php/topic,15056.0.html

I'm finding very little info on how to power devices from an arduino pro mini as I would an arduino uno, etc.

I'm trying to figure out how to successfully power an s3003 servo powered directly from the ardiuno mini. As currently set up it works fine when powered by usb cable (so regulated not raw input). However when I connect a 9 or 12v 1 amp dc wall adapter to the raw/vin pin on the arduino the device seems to continually reset I'm guessing due to lack of power.

Can anyone help me with this? I read a comment on sparkfun that said unregulated power has a maximum supply of 150ma to things connected to vcc. On another post it says the s3003 apparently only draws 65ma, but when I test with a multimeter on an Uno it seems to draw 200ma. Can anyone confirm if the 150ma limit applies to the 5v version of the mini? I'm surprised it works over usb but not over unregulated.

I think I have two options. 1) I can take a 5v 2amp dc wall to usb adapter (which works when plugged in as usb), snip the end and connect it to vcc. Or I could snip the end and connect it to vcc, AND connect the servo directly to it, instead of going through the board.

What makes the most sense? Or other options.

Thanks.

150mA, its just a little tiny regulator. Option 2, power both from the wallwart in parallel.

The S3003 has sometimes a peak in the current. I assumed it was about 1A, but I read that someone measured it and got 500mA for the S3003. That is too much for Arduino boards.

Just to test a servo, using the 5V of an Arduino board often works, but I guess you had bad luck. The only way to power a servo, is using a power supply of 5V (or 6V) for the servos. You can use it to power the Arduino also, as you wrote in option 2 and as CrossRoads wrote.

CrossRoads:
150mA, its just a little tiny regulator.
Option 2, power both from the wallwart in parallel.

Thanks. I might be missing something fundamental about how regulators work but hear me out. If I put regulated (the 5v usb adapter) directly into the RAW/Vin unregulated input, the servo works fine. Which is drawing 200ma, so a 150ma max seems to not apply at 5v?

IF I put the 5v into VCC, it of course works as it’s more or less directly connected, and if I run them in parallel it also of course works. So with all three options I actually get the same behavior. No greater performance or consistency in either way.

Having said that I think the option I will go with is hooking it up to VCC as I already have the servo wired to the board. But I would like to understand why 5v works through regulator but not 9 or 12 volt.

You should not power the servo via the board. That is all you have to know.

The newer voltage regulators (as used on the Arduino boards) are able to ouput a voltage which is very close to the input voltage. So if you use 5V as input, the output is almost 5V. And the voltage regulator can supply more corrent since it is almost not getting hot.

If the voltage regulator gets 12V, it makes 5V. The 12-5 = 7V is making the voltage regulator getting hot. To protect itself, it turns down the current. For example 200mA with 7V = 1.4 Watt. That is a lot for such a small component.

Thanks! That explanation helped me understand that better. I’m curious about the reason not to ‘bridge’ the servo across the board. When I look at the circuits on the board it looks like all the VCC pins have an unobstructed path to each other. Shouldn’t connecting it like that basically be no different than doing the servo and arduino in parallel from the power brick?

Thanks.

I see two Vcc pins on the Pro Mini board. Those are the same.

You could use that voltage regulator, even with 5V. So the adapter/walwart to the servos and to the RAW pin. In that case, don't use the Vcc, or only for a sensor or something like that.

Ah ya sorry you're right. For some reason I thought there were 3 vcc and one raw.

OK so my plan of attack was to go from walwart at 5V to one VCC pin. Thus powering the arduino. Then the other VCC pin I have split to both a LDR photocell and to the 5V in of the servo. Not using the regulator. Does that make sense?

Like I said I tried all three power options and I seemed to get the same result. Just wondering if there's some hidden issues with one way or another.

Some reported that powering the 5V to Vcc could damage the voltage regulator in some rare cases. But it is valid to do so. It's not a problem.

But using the servos on the other Vcc, I don't like that. The current and servo noise is going through the pcb of the Arduino Mini. The circuit board is not designed for that. On the other hand, it is just a small servo motor. So if it is only for testing, it will work.

Thanks. It's for daily use, (http://www.youtube.com/watch?feature=player_embedded&v=eIBqo3i9DPA).

I think I'll run it in parallel then given what you said. Makes sense but I wondered because as a lazy factor I like the idea of just soldering to contact pads rather than splitting wires.