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Author Topic: Arduino as a Simple Power Source  (Read 2967 times)
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In my experience, chip damage is rare but when it happens it due to serious abuse like a short circuit.
I do think its important to advise people new to electronics to be careful to wire things up correctly and double checking for correct  polarity and voltage.

But I remain doubtful that running a few pins at current greater than 20ma (as long as absolute maximum ratings are not exceeded) will smoke a board

I am happy to have my eyes opened on this, perhaps someone here can say if they know for sure if this has happened.



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Heck, I'm just happy if I can convence newcomers the need to use series resistors with their LED's, let alone warning them about running too close to the absolute max specifications.  smiley-wink

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Hi Lefty, I am surprised how many times I have seen newcomers connect an LED without a resistor.
Also, some people think because standard Arduino boards have an internal LED in series with the resistor on pin 13 that its ok to connect an external LED across that pin.

Anyway, my advice to Arduino beginners is:

The Arduino chip is robust but it can be damaged if you abuse it. Be careful to properly select and wire your components.
The Arduino chip can provide up to 40ma per pin with a total current of 200ma across all pins but it is good practice to keep well below these absolute maximum ratings if you can.
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OK but my advice is keep the current to 30mA as the absolute rating will eventually kill it.

Also you can spread 350mA across the ports providing you have half of the pins sourcing and the other half sinking so that any one power pin does not exceed the 200mA maximum.

I know we are not designing products here but beginners often get into building large systems after very little experience. Electronics like chemical engineering and home cooking don't scale up in a trouble free way and if the foundations are wrong you stand even less chance of getting it right.
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London
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OK but my advice is keep the current to 30mA as the absolute rating will eventually kill it.

Hi Mike, is that based on any practical experience with ATmel chips?

« Last Edit: July 12, 2011, 02:43:57 am by mem » Logged

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No that is based on half a lifetime of derating components for commercial and hobbyist projects.

While the projects we make here are only one off, once they are out on the net there may be several hundreds made or bits of the design incorporated into other projects. That's how we start to design, take a bit of circuit from here a bit from there and put them together. So I feel that it is best if start off with some simple ground rules and make any design repeatable.

I did some tests and was able to get in excess of 250mA pulsed output from an arduino pin, there is a misunderstanding that some how the arduino processor limits the output to 40mA by itself.  This leads to things like not putting resistors on LEDs and that gets propagated and beginners come on here with problems that are exasperated by overloading the output pins. 

Good to have you back again by the way.  smiley
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Thanks, good to be back

I have seen people connect LEDs without resistors in a number of workshops. Hopefully, advice from knowledgeable  people such as yourself and CrossRoads does help to keep chip abuse under control.

I just don’t think that tinkerers should be scared to go above 20ma if they need to.

Michael
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I just don’t think that tinkerers should be scared to go above 20ma if they need to.

Sure, but they need to be aware of the risks...  The damage they do may not show up for a while...   Catastrophic damage lets the magic smoke out pretty fast so the relationship between damage and abuse becomes understood while tinkering.  The other side of that coin is that habitually exceeding data sheet ratings will not be apparent immediately but can seriously shorten silicon chip lifetime.

Abuse an LED with 5 volts... it magically is OK afterward... but you probably shaved many hours off its lifetime if you left it connected without that current limiting resistor.  I use that as an example since the abuse can eventually be "visible".  Arduino PIN abuse is not so visual... and could break on the "tinkerer" just when they want to show off their new project.
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London
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Sure, but they need to be aware of the risks... 

Its a little unclear how realistic those risks are.

Experienced engineers derate components as a matter of good practice. And it’s good advice for hobbyists. But I would be interested to see any evidence to show that running a pin between 20ma and 40ma would make any practical difference to the life of the chip. 

Are there any Atmel engineers out there taking a busman’s holiday on our boards?
I think it would be good to know if running above the 20ma safety margins advocated here really are abusive to the chip.
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If you are concerned about proper engineering practices: what about proper software engineering practices? The Arduino platform lacks version control, life cycle management and debug support. Also most hobby projects have probably no kind of quality control.

With regard to electrical engineering, ESD measures are ignored in 99.9% of the cases.

Having said that why should it be such a big risk to overload some pins? If you want to decrease risk it is definitely not appropriate to look at just one risk in isolation. You need risk management. This comes at some cost. I doubt that this is justified for most hobby projects.

If you have any significant risk in connection with your projects you most probably do not want to run it on a hobby platform at all. I think most hobbyists are prepared for letting the magic smoke out.

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“I am completely new to Arduino/electronics etc,”
“I'm not sure I understand what "sink" and "source" means. “
...
"I think most hobbyists are prepared for letting the magic smoke out."

I think I'd have to disagree with you on that. I think most hobbyists have little to no knowledge of electronics, do not understand datasheets, limitations on parts, etc.  Take someone like baum for example, an active experimenter, posts a lot and tries different things, yet didn't understand enough about the arduino board to be confident about removing the '328 from its DIP socket.

"But I remain doubtful that running a few pins at current greater than 20ma (as long as absolute maximum ratings are not exceeded) will smoke a board

I am happy to have my eyes opened on this, perhaps someone here can say if they know for sure if this has happened."

Yes it does:
In some of my early prototyping, I was driving some unknown NPN transistors (25+ years old, had a small drawerful I want to use up) directly from an arduino pin to control a couple of LEDs in series from 12V while I experimented with current limit resisters to determine brightness (and 10,000mCD white LEDs are really bright!).  
Finally got the brightness level I wanted with some 5-6mA of current, and let it run (not blinking or anything, just on) for a few hours while I fiddled with code. At some point I looked over and it had gone out - and then I discovered the ATMega was very hot! So not having a base resister let Atmega overcurrent and eventually fried the pin and killed the chip. (and then I got to discover how to bit-bang a bootloader into a blank part)

I also have a dead Promini because a wire I thought was plugged onto a wirewrap pin wasn't, while handling the box I was testing it brushed the promini and fried it.  So I can attest they don't take too much abuse.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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As a hobbyist I reserve my right to abuse my $5 328p chips anyway I wish. I laugh at your 20 ma limit recommendation. Nobody is my boss anymore (accept maybe she who must be obeyed  smiley-wink )

Note: I do recommend not wiring +12vdc to a analog input pin like I did to a 644p chip on a breadboard once. The results were instantaneous, it made a snapping sound and I saw a brief spark and ended up with four dead I/O pins. However the rest of the chip still functioned.  smiley-wink

Lefty
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With regard to electrical engineering, ESD measures are ignored in 99.9% of the cases.

It is a well known fact that electronic engineers have never been known to damage a chip through static. Where as girls that work in factories will, unless precautions are taken.

I put this down to engineers, in general, not wearing nylon underwear.  smiley-wink
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I put this down to engineers, in general, not wearing nylon underwear.


Nah, it's just that girls are much 'hotter' then guy engineers. And the rumors of sightings of actual girl EEs in the workforce is just a myth.

Lefty

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the rumors of sightings of actual girl EEs in the workforce is just a myth.

You wouldn't believe that if you worked at my office. Including engineering management.

Too late for me, I'm retired. However the keypunch operators in my field engineering days in the 70s were fun to be around.  smiley-wink
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