arduino pro mini question

i'm having an issue with powering my arduino pro mini (5v). i am currently running two servo motors with the pro mini and i have it running exactly the way that i want it when it's connected to the FTDI Basic USB, but when i connect it to a 5vdc wall adapter, it doesn't run the same. the servos don't move the same way, almost as if they are constantly resetting. so i currently have the vcc connected to the postive end of the power source and the ground connected to the negative. i even tried connecting the reset to 5v to possibly prevent it from resetting but that didn't work - so i don't think that it reseting is the issue. am i completely missing something? i have searched so much to help figure out this issue, and i haven't been able to find anything. any help would be very much appreciated! :) thanks

Is it a regulated 5 V wall wart? Not likely.

Most likely, it's rated amperage is less than the Arduino and servos needs. The voltage drop when the servos kick in may result in too little voltage to power the Arduino properly, too.

The on-board voltage regulator needs more than 5 volts to create the steady 5 volt output that makes the Arduino happy.

forgive me, i'm still a bit new to all of this - but the one i'm using now has an output of 5v/500mA, Input: 110-220V, 50-60Hz would something like this be better? http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=12923

That should do.

that was simple enough, i'll get myself a couple of those and hopefully all my problems will be solved! thank you very much

If that solves ALL of your problems, let me know. I'll get one too, for that price.

just curious - would this also be a good solution (a more expensive one, ofcourse) http://www.sparkfun.com/commerce/product_info.php?products_id=114 with like a 9v wall supply?

If the wall wart that you posted the link to actually does output a constant 5V, it would work.

The sparkfun item will output a constant 5V (or 3.3V), so, it would work, too. For it, though, you need to supply a higher input voltage. Anything from 6 to 12 volts.

I have 2 walls warts that claim to output 7.5 volts. One drives my breadboard voltage regulator circuit just fine. The other does not. So, I'd be looking for a wall wart of 9 volts or so to supply power for the sparkfun voltage regulator.

In general you cannot expect to use a "wall wart" to directly power your devices: you need a regulated power supply (like that Sparkfun one) between the two. Here's a little explanation:

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=103

Most of the wall warts that come with your consumer electronic devices are supplying electricity to a regulator circuit inside the device, and not supplying it directly to the device's components. Tear apart an old device sometime, and you'll see a voltage regulator, diode, and capacitors next to the place where the wall wart plugs in. Unless the wall wart is really regulated, you need those.

I've been using the Sparkfun 3.3V/5V supply for a lot of projects recently, and it works well (in fact I have two of 'em). For practice with Eagle/BatchPCB I just ordered up the stuff (boards, parts) to make a couple of 3.3V supplies with roughly the same design, as well: you can never have too many regulated power supplies.

Most standard regulators put out a certain voltage only if they are supplied with a higher voltage (apparently sometimes as much as a couple of volts). There are "low dropout" regulators that can supply a certain voltage with an input voltage that's only slightly higher than the desired output voltage. For example, I'm getting a good 3.3V out from a LDO regulator that's taking about 3.7V in on one of my boards - that's powering a Pro Mini 3.3V just fine.

I'm only just learning about this stuff now, and some of my learning has involved the de$truction of part$.

Apparently it's also true that if the input voltage is TOO much higher than the output voltage, you also generate a lot of heat, so more is not necessarily better. I've been mostly using a 6V wall wart as input to the Sparkfun power supply. However, I have come across situations in which that 6V wall wart didn't work but a 7.5V one did. I assume that's a matter of "dropout".

thanks for the advice! i got myself a couple of the sparkfun voltage regulators just in case as well as a couple 9v wall warts. i'll be experimenting quite a bit these next couple of weeks. thanks again

A little piece of advice: check the voltage output from your supply, whatever form it takes, before connecting expensive parts.

I have also learned recently about two other issues: reverse voltage protection, and maximum current supply.

Make sure you can't hook up the leads backwards, and if you're putting together your own supply, put a diode in there. I fried one regulator (on a $19 board) by momentarily touching a 9V battery backwards to the leads.

Also make sure that you know how much current your regulator can supply. If it's a TO-220 package at 3.3V or 5V, it's probably in the range of 800 mA to 1.5A (based on the couple I've worked with). If it's just a T0-92 it's probably more like 250 mA or less. If it's a surface mounted one, it's also probably no more than about 250 mA (and maybe quite a bit less). I made a lot of smoke a couple of weeks ago by consistently drawing more than 250 mA through a surface mounted regulator that can apparently only supply about half of that. You wouldn't think they could fit that much smoke into such a tiny part.

Motors*, radios (esp. transmitting), processors, LEDs and such require a lot of current. Sensors apparently generally don't. I've been ignoring the current requirements of my devices for about 2 years, and it has finally caught up with me. Eventually you'll need to pay attention to those things, or you'll find yourself paying the price.

  • Motors require so much that you'll almost certainly need to give them their own power supply, and there's all sorts of isolation stuff you need to do to control them through a processor. Fortunately there's lots of information on this. Definitely read carefully before you try to control motors.

thanks again for the advice, really appreciate all the feedback! i've already tried the regulated 5v wall wart, and it is currently working wonderfully with my arduino pro mini and two servos. i've assembled the 5v/3.3v regulator, just waiting for my 9v wall wart to then test that out. thanks again