I am using an Arduino Pro 328 5v to run a 7-seg display and a solid state relay for a small project of mine. Via USB I had everything running perfectly and was very happy, when I connected my creation to an external power supply, things started to go wrong. The first one I used was the sparkfun 9v wall wart. Wall Adapter Power Supply - 9VDC, 650mA (Barrel Jack) - TOL-15314 - SparkFun Electronics
Using external power, all the LEDs would flicker from time to time, and a multimeter across the Vcc and GND showed that the board's 5v would drop below 4v while this was happening. I wondered if it wasn't supplying enough power, so I tried a beefier 12v one I had lying around. To my horror the magic blue smoke was being released from my precious Arduino. It still works via USB, but I am pretty sure the ability to power it up via a 2.1mm jack has been lost.
SO, enough rambling story, I two group questions:
What should or shouldn't I be using in the future as far as wall warts go? Was it the dirty DC coming from the wall wart that caused my power to falter and then later fizzle?
It still works via USB, so I am thinking I could give it 5v via the FTDI pins with one of these sparkfun 5v supplies: SparkFun Breadboard Power Supply 5V/3.3V - PRT-00114 - SparkFun Electronics. Would that work? And should I just plan on having one of these for every project? They say the Arduino board can handle 5-12v in, but it seems like that is only semi true.
Sorry for the long post, I wanted to get all the detail in there. Thank you for any help, I am new to electronics, Arduino and this forum, and am eager to learn.
It's tough to know without exact details of your circuit, but let's suppose the USB-powered system was running fine while drawing the maximum 500mA of current. I don't know why an LED+SSR system like you describe would be drawing that much current...but that's another issue.
With a 9V input, the voltage regulator on the Arduino was dropping 4V (from 9V-->5V) while conducting 500mA of current, thus dissipating P=VI=0.5*4=2 Watts. That's a lot of power for the regulator and it could be going into thermal shutdown thus limiting its output current (which will cause the voltage to go down too).
With a 12V input, it's now much worse, P=VI=0.5*(12-5)=3.5 Watts and the thing will get even hotter.
Thermal shutdown is SUPPOSED to kick in and protect the regulator, but nothing is perfect.
My best guess is your regulator is toast and you have a miswired circuit somewhere that is drawing too much current. Do you have a schematic?
Can you see what part is damaged?, is it the regulator or is it maybe a Electrolytic Capacitor?
I have checked the board, the power regulator can do max 150ma.
There is no protection diode for reverse +/-. So its probably build in the power regulator. But the capacitor before the regulator isn't protected, that could be blown up.
So check if the +/- was correctly done, if it was wrong, the cap is blown.
And the most likely reason the 9v adapter didn't work is the max current is 150ma for this version. and USB can do 500ma
In response to RuggedCircuits, I don't have a schematic, and my hand drawing of one would probably be useless. Most of what i did was copied from the documentation with my 4511 BCD for the 7-seg displays. I know the way I have the solid state relay setup only draws about 2ma. I don't think there is a problem with the display, but I will poke around to see if I can find a short.
In response to SuperCow, The part damaged is between the transistor, and the thing with the F on it. Directly above the P of power in this picture. It has a nice little hole in it.
I soldered on the DC barrel power jack directly onto the spot it would fit, so that is probably correct, don't see how the +/- could be backwards. Also I didn't know that the max the board could handle only 150ma.
I was positive that my soldering / wiring for the display was correct, but from what you guys are telling me it looks like I might have a mistake. I will start by trying to figure out how much current the display is drawing. Thank you very much for your responses.
That's a 10uF capacitor. Those generally don't release smoke unless voltage is applied backwards or excess voltage is applied. Could be you have a bad power supply which is way above 9V, or maybe the power supply output is reversed (though that wouldn't explain the voltage output of 4V you observed).
AHHHHH Ok, mystery solved. That beefier 12v wall wart I hooked up outputs 12v AC, NOT DC. So the lesson of a day is not every black boxy thing is an AC/DC converter. So that explains the damage.
Each of the LEDs in my display has a resistor in line, and in measuring across that resistor I found about 15ma per segment. I have 2 digits, that is 14 segments, so that puts me over my 150ma limit.
So in final let me see if I can sum this all up. I can power Arduino + stuff on 5-12v so long as Arduino + stuff < 150ma. If, and this is where I get a little fuzzy, I supply 5v, then I can go over 150ma with my board and attached stuff to some reasonable amount. Are all these true statements?
Thats a cap with the burn mark You can replace it than it "should"work fine again.
Your statements are true.
If you power directly 5v you can get alot more ma, up to 1 amp.
But it has to be a regulated power supply, USB or a other adapter.
I recommend to make a own small one, with a 7805 regulator like this: http://www.circuitsonline.net/img/000025.gif
(the 1000uf cap can be a 100uf) You can supply it with your 9v adapter.
With respect to the LED's, note that multiplexing is a common technique for reducing power. The idea is you only light 1 LED at a time, and you switch between lighting them quickly (e.g., 100 Hz). You can do this in software (somewhat complicated) or use a driver chip that does this for you (e.g., MAX7221). This dramatically reduces current consumption and the human eye can't notice the flicker if it's fast enough.
You can power Arduino+stuff on 5-12V FROM AN EXTERNAL SUPPLY as long as the current draw is <150mA. When powering from the USB port, you can draw up to 500mA.
In practice, however, I don't like living on the edge. You may not want to be right up against 150mA and 500mA respectively, continuously. Stuff happens.
Well I think I have it all straight for now. I know where the edge is and will try to stay far back away from it now on. I have on order a 5v regulated power supply kit to start with, and if that works i will try building my own regulator circuit like SuperCow suggests.
Thank you all for your time and suggestions, you have been very welcoming to a questioning newcomer.
