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Author Topic: Driving Mega2560 from external 5V bricks USB port  (Read 10073 times)
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That reminds me, one of the Megas I bricked was an R3 from Radio Shack. They took it back, no questions ( < 30 days).  So the r3's brick as easily as the r2's.

The others were evilbay items. Tough luck.

Good reason to buy these things from established vendors with return policy.
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Is this USB bricking on 5V external power confined to the Mega? Anyone heard of it on the Uno or Nano?

I am planning on hooking a Nano to my backplane. Don't need another brick. I'll contact Gravitech (manuf) and see if they will warranty it.
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Hello,

David Cuartielles from the Arduino Team here. I have been following this discussion trying to figure out what has been going on in this case.

Please note the following. We do not recommend connecting the Mega boards powering them from the 5V connector. Not the Uno R3 either. The voltage regulators we were using in the past (Arduino Serial, NG, Duemilanove, Diecimila, and part of the Uno's) would allow doing that. But the new way we use to bring power into the boards will not ensure the boards to work properly. That 5V pin is meant to be used to power sensors and low-current devices.

The fact that this issue is showing after a certain amount of hours of operation seems to be due to stress material. However I am just talking without scientific proof. Our hardware team is going to put some boards under test to check this point and see if there is a deterministic way to measure how long the boards run on this mode. I know this will not be of any help for your project as you seem to be interested in powering things from that 5v connector.

On the other hand, since our previous boards allowed this type of functionality, when documenting the new boards we copied material from the documentation files to the previous boards. There is one line about the 5v that says (and I quote textually):

Quote
5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.

.. that last part should not be there:

Quote
or be supplied by USB or another regulated 5V supply

If you want to power up your boards you should be using the Power Jack, Vin, or the USB port.

This is obviously an error on our side and we will replace the original Arduino boards you got bricked. Please send me an email to: d.cuartielles AT arduino DOT cc with the serial numbers of the damaged boards and their models. Include your preferred shipping address. I will make sure the same boards are shipped to you the minute after I get that email.

I am sorry for the non-Arduino branded boards. As you know we don't support those.

Thanks for your understanding and thanks for helping us finding out this error in our documentation. We will fix that immediately.

/d
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Hi David. Is there any chance of getting a switching regulator with a wider input range?
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I think that being able to be powered by 5v directly is essential functionality.
Many times people only have access to a 3-5v source that can be connected directly to the 5v pin.
In many cases 6.5v or more cannot be obtained.
It seems like a redesign maybe needed. Have you considered ultra-low voltage dropping diodes?
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David,

I want to thank you and the entire Arduino team for standing by your products. The offer to replace the boards is very much appreciated as each and every board we purchased was intended to go into the first actual customer installations of a new product. Getting to this point has been very expensive for the new co. that designed and built the first prototypes of the new product. Even though the Arduino's were among the less expensive of the components involved every little bit helps, and the replacement boards should hopefully end up in the hands of actual customers (buried inside little black boxes!).

Your reply, and the honesty within is very much appreciated, and we will do all we can spread the word that Arduino and the people behind it are a good investment.

Now then, (and grinning) - while you're changing the mega2560 documentation on the web site could you please get somebody to fix that broken zip file containing the reference design for the rev3?

Thanks,
Kurt Olsen
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Maybe some of my bricked Megas can load sketches from their ICSP ports.

In my case, the mega's with dead usb ports could still have sketches uploaded via the ICSP.
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Hej,

even if this a little bit off topic. I changed the files for the Mega ADK and Mega this morning. I just double checked a second ago that the files can be downloaded and that they uncompress with no problems. You should make sure you are using Eagle 6 or later to open those design files. We are always working with the latest version of Eagle and those files were generated with those.

Again, we identified a communication problem between our editorial server (the one where we prepare the documentation for you)  and our production server (the one you get documentation and files from) after we moved the whole server to a much more powerful machine. This problem includes that the zip files when copied from one server to the other they get corrupted, they loose the last two bytes.

I haven't been able of identifying the reason for this yet. Better said, I know why it happens, I just haven't figured out how to solve it in a way that doesn't imply a big hack to our current proxy server. So we have to manually upload the zip files to the production server after we have published the page and for the new R3 Mega and Mega ADK we didn't notice in the first place.

Thanks,

/d
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Hi David,

Thank you, unfortunately the changes to the mega2560 zip file haven't taken effect yet (from hawaii), here's the link that the web site gives me:

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-reference-design.zip

Thanks for working on this, I'll try again later.

Mahalo,
Kurt


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Hello all!  I recently ran into this same problem, and I wanted to share my workaround for getting away with using an external regulator without wrecking the USB connection.  Obviously I can't be 100% certain that this will fix the issue, but so far my mega board isn't bricked yet so hopefully it will continue to work.

There are two problems with using an external regulated supply.  First, at least what I've read from this thread, it seems like the onboard voltage regulator is not as tolerant of reverse voltages as on other Arduino boards.  To fix this issue, I simply removed the external regulator from the board.  I used hot air to desolder the regulator, but I'm sure you could remove the regulator just by prying it off (should probably cut the traces first to avoid delaminating too much of the board if you try it).  I guess I should mention that I'm working with the Mega Pro 2560 5v board from Sparkfun.  This is probably not the ideal solution if you're using the Arduino board for different projects, but in my case the board I'm using is part of a permanent project, so having to remove the regulator is not such a big deal in my case. 

The second problem is that, with the configuration I usually use to program the Arduino (FTDI basic breakout, again from Sparkfun), The 5v USB supply and the 5v from my external regulator are both connected together, which can act like a short circuit.  In theory if two ideal voltage sources are wired together, unless the two voltages are exactly the same, there will be infinite current flow between the two voltage sources.  It may work out that under certain conditions this is something you can get away with, but based on the fact that people's boards are getting bricked that doesn't seem to be the case here.

Here's my workaround.  Instead of using my usual FTDI board I bought just a straight breakout bord of all the FTDI chip's signals (http://www.sparkfun.com/products/718).  In the FTDI datasheet, it explains that the chip can handle two separate power supplies.  The power from the USB host should be connected to the VCC pin (which it is in the breakout board I linked to), and the power from your external regulator should be supplied to the VCCIO pin, which acts as the supply for the UART end of the FTDI chip.  Conveniently, the voltage on VCCIO doesn't have to match the voltage supplied on the VCC pin.  Now, in the breakout board I linked to, VCC and VCCIO are connected together by a solder jumper.  If you just cut the jumper with a knife and connect your external 5v (or whatever voltage you're running your Arduino at) power to the VCCIO pin.  At this point you just have to wire the breakout board to a connector so you can attach it to the serial programming header on the Arduino board.

If you do both of these things, then there's no chance of current back-flowing through the regulator, and there are no power supplies that are shorted together.  Seems to be working for me so far.

If there's anything I've unintentionally been unclear about, just let me know.
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I'm glad that I saw this thread  before I hooked up my Mega, it saved me a ruined board. I'm running off of a 80's vintage backplane, with a typical 5v supply. The supply runs hot, about 5.25 volts. Thanks to seeing these posts I disconnect the Mega2560 from the external supply while programing, then disconect the USB when installed. Works so far. The one time I left the USB conneced when attached to external supply, the Mega USB IC got hot fast.
I also use a modified USB cable with the 5v line cut for when I need to get data while running.

Since the problem is known and can break boards, how about a sticky, or a warning.
Get the word out
.

Thanks
Bob Prescott
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I'm glad that I saw this thread  before I hooked up my Mega, it saved me a ruined board. I'm running off of a 80's vintage backplane, with a typical 5v supply. The supply runs hot, about 5.25 volts. Thanks to seeing these posts I disconnect the Mega2560 from the external supply while programing, then disconect the USB when installed. Works so far. The one time I left the USB conneced when attached to external supply, the Mega USB IC got hot fast.
I also use a modified USB cable with the 5v line cut for when I need to get data while running.

Since the problem is known and can break boards, how about a sticky, or a warning.
Get the word out
.

Thanks
Bob Prescott
0.25 is alot of differential between two power supplies. Enough to dissipate several hundred milliamps in the board.
With < 0.1v differential, I don't really see why it would be a problem but with .25, I would avoid it.
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In the original post, I mentioned that the differential  between my external 5V supply and the USB power was < 100mV.  Generally less than 25mV, every time I checked. I still bricked the USB ports of several Megas. I wish I had checked the temperature of the chips, but it took me a while to localize the problem, because they did not appear to fail at once. It was only when I tried to reload sketches that I realized I had a problem.
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.25 is a hugh differance, I know, and old power supplies designed for TTL usually had some kick. But it really only matters if power supplies are shorted together, which is unexpected.   I'm sure I can open the supply and adjust it down. Might have to change a resistor.

What does irk me a bit, is that I picked the Arduino Mega2560 specifically because it could run off of an external 5v supply.
Now I have to kludge a wall-wart, and redo my shield to separate supplies? I guess  I'll live with it, not the end of the world.

Bob





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Quote
.25 is a hugh differance, I know, and old power supplies designed for TTL usually had some kick.

My experience  was with a  differential of 0.025V . That does not seem to me a so big as to account for the failure of an IC. I suspect something else is involved. Could the unplugging and plugging of the USB cable while connected to an external 5V supply generate some kind of spike or reverse voltage?
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