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[on:]

Hi,

So I just bought some 5,1K resistors to drive a LED on my arduino MEGA and when I came back home I just plugged everything in, without any concern, I was just going to light up a LED using a resistor.

BUT, the LED was VERY bright. Too much. I realised that the f****** seller at the electronic store sold me the wrong resistor values!

I unplugged everything as fast as I could and saw that it was aproximatly 7 ohm resistors!

Now when I power my arduino, the atmega is heating up slowly.

I can still use my pins and upload sketch.

Does anybody have replaced or knows how to replace an ATMEGA 2560?
In fact, I just don't know what to do. I don't if it will heat up too much after a few minutes or if it will stabilise.

After one minute the atmega is just warm.

Any idea?

[Reply #1 on:]

Do all pins work ok including the pin you used for the LED?
I would say are you certain it wasn't doing this before?

[Reply #2 on:]

I haven't checked all pins, but the pins on wich I wired the LED is still working.

I'm also certain it wasn't doing this before, I often check for temperature on the board.

[Reply #3 on:]

How many LEDs did you have hooked up? Was was there any other hardware connected?

While it is possible this could cause this kind of damage, it seems unlikely.  Many, many, many people connect LEDs without any current limiting resistors and do nothing more than blow the I/O pin.

At 16MHz it is rare for these processors to get hot to the touch, in relatively low ambient temperature.  So if it is getting hot to the touch, it is probably a bad sign.

[Reply #4 on:]

I hooked up 1 LED.

pin 6 connected to the resistor, resistor connected to the LED anode, LED cathode connected to pin 5.

pin 6 was OUPUT HIGH
pin 5 was OUTPUT LOW

the resistor was supposed to be 5,1K but was like 7,2 ohm.

It heated up for the second it has been plugged in, and now it heats up (gets warm in a minute and increase) every time I power it (nothing connected).

Would it be possible to replace the ATMEGA 2560?
I could try to find somebody able to do it nicely.

[Reply #5 on:]

You can just google the chip and find somewhere to buy it, then solder it in yourself. However, a SMD of that size and number of pins would be really hard to do, but if you can do it or have a friend that can do it, go with that.

I would wait for the chip to stop working first though. Especially if it just gets slightly warm to the touch, it won't do anything bad to the rest of the board - the worst that can happen is that it can stop working.

[Reply #6 on:]

To ME (i am not 100% sure):

ATMel I/O ports can source / sink a maximum of 40mA per pin. And according to the port. Some ports are grouped together and have a specific cumulated current capacity.

If you go beyond those values .... they say the chip can be damaged ...
...so my best guess is that your board is on a wrong slope.

Just a little story:
I have just blown 2 ATmega1280  IOs when using a supply of 9V and sourcing current from one pin while sinking the same current on another pin (like you with your LED) .
When using my board for other purpose I had strange behaviour. I found out that the output HIGH level was not 5V but .... 7V !!!!!!
All the pins are dead now  

[Reply #7 on:]

@AUREUS
Do NOT supply the chip with 9V.
It requires 5V.

[Reply #8 on:]

Thanks for your infos.

I'm gonna keep it until it burns and then I'll try to change it.
I'm also gonna take a further look at the datasheet about what AUREUS said:

@AUREUS

ATMel I/O ports can source / sink a maximum of 40mA per pin. And according to the port. Some ports are grouped together and have a specific cumulated current capacity.

And luckily the shop who sold me the wrongs resistor values will pay me an ATMEGA2560

[Reply #9 on:]

I'd guess that the chip is dying right now.

But, and don't get me wrong here, this is what happens when you don't know exactly what you are doing.

Arduino is great because it powers people to do something they thought about without having to get a Phd or something like that and proof of that are all the projects that have come up made by people with little electronics experience or knowledge...

But there are still things you need to know, specially when creating hardware connections. It's true that the seller made a mistake (purposedly or not, is not the point), but you should have checked the resistor color code before connecting the resistors. It's an expensive lesson to be learned this way.

Also, I don't know what you told the electronics shop guy, but 5,1k is a bit too much to control a LED... you won't get nowehere near it's "safe" brightness limit. And maybe he thought (an error on his behalf) you would source the LED from the Arduino and then 7 Ohm would be acceptable (considering the resistor inside the Arduino). Actually, the 7 Ohm would be a waste... but he has to make a living.

In the end, the guy in the electronics shop made a mistake. Either because he tried to interpret your order and change it to what he thought best or simply made a mistake. However, you should have still checked the values before connecting. It's one of those things that you learn with experience... Too bad it might have cost you the ATmega2560.

[Reply #10 on:]

I've got a chinese arduino (DFRobotics) that when a 9v battery is connected to the external power connector, the arduino 5v pin reads ~7.5v and 8v+ when 12v is connected. Seems the external power voltage regulator is defective.

[Reply #11 on:]

@zoomkat   : indeed I also have DFRobotics boards and I am having the same issue:

- when powering from the jack plug with +9V or +12V, the +5V pin is above 6.5V
- so I tried using a voltage converter R78B9 (5...36V converted to 9V 1amp) on Vin pin and I have the same behaviour.
- now I am using a R78B5 directly connected to +5V pin, and I don't the issue, but I have another issue:

the board does not behave the same when powered first from USB then connecting to +24V (so USB and +24V together) , or when doing the opposite: first starting from +24V then USB  (so USB and +24V together) .

I guess I should open a thread about how to power the board ..