Why arduino can fry?

Hi,

Today a read that my arduino uno can fry by conecting a DC motor direcly into one of the i/o pins. Anyway my question is why can it fry my arduino?

This may look a ridiculous question but I hope you can answer to it.

thanks.

Becasue the DC motor will have a very low resistance, and the AVR will exceed its 40mA maximum rating trying to drive it.

Thanks for the reply and for moving my topic.

What is the AVR?

Sorry for being so anoying.

It's the microcontroller on your Arduino.

why can it fry my arduino?

Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them.

Motors are inductors who will try the best to sustain its status quote. If the current going through it is cut off, it will create a significant voltage trying to sustain that current. That voltage is higher if the cut-off is quicker.

So w hen your io pins turn off fast, that huge voltage is applied to the pin -> causing it to go to the avr heaven.

Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them

You've done this?

Thanks for the reply's and the support.

you guy's answered my question very fast.

Thanks.

Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them.

You've done this?

I guess Atmel doesn't know what they're talking about when they give the current limits, both per-output and per-device, in the datasheet.

The simple fact is, you kill the arduino (actually the ATmega) by trying to draw more current than the chip is designed to handle.

-j

kg4wsv:

Low (dc) resistance isn’t the issue: you can actually short your avr’s pins without damaging them.

You’ve done this?

I guess Atmel doesn’t know what they’re talking about when they give the current limits, both per-output and per-device, in the datasheet.

The simple fact is, you kill the arduino (actually the ATmega) by trying to draw more current than the chip is designed to handle.

-j

A short will either shut the regulator down for the DC input or open the PTC (fuse) for the USB. An overload could easily destroy the outputs. This is one of the reasons I cringe when I see people recommend that an LED being directly connected instead of through a resistor as an LED (or any other diode) is a short that just opens up below a certain voltage.

A short will either shut the regulator down for the DC input or open the PTC (fuse) for the USB.

Yes, but that happens well after you hit the per-pin limit of 20mA.

It protects the regulator, or the device on the other end of the USB cable, but it won't do all that much to protect an overloaded output pin.

-j

dhenry: you can actually short your avr's pins without damaging them.

Yes, if you leave the Arduino powered off, or have the pin configured as an input or as an output set to the same level as the thing you 'shorted' it to.

Otherwise, I can't imagine what gave you the idea this was true.

I can't imagine what gave you the idea this was true.

To design a robust product?

kg4wsv:

A short will either shut the regulator down for the DC input or open the PTC (fuse) for the USB.

Yes, but that happens well after you hit the per-pin limit of 20mA.

It protects the regulator, or the device on the other end of the USB cable, but it won't do all that much to protect an overloaded output pin.

-j

That's why I specifically said "short" and not overload as you would have to overload all of the pins at the same time. Still a bad idea to do. BTW, don't the UNO specs say 40 mA?

AWOL:

Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them

You've done this?

FWIW... I've accidentally shorted outputs and even inserted the 328P backwards... never hurt the chip (yet).

Of course, in reality the datasheet specs MUST be adhered to or else the chip WILL get ruined sooner or later.

BTW, don't the UNO specs say 40 mA?

Yep, the ATmega datasheet says 40mA absolute max per I/O pin, 200mA max for the device. I mis-remembered when posting earlier.

-j

I've accidentally shorted outputs and even inserted the 328P backwards

You are in good company there, :).

People screaming about "damages" here simply have no idea what they are talking about; or don't understand the datasheet when they quoted it as support.

Some OEMs went so far to specify shortcircuit current.

People screaming about "damages" here simply have no idea what they are talking about; or don't understand the datasheet when they quoted it as support.

Hey! Look people - we've got our very own troll.

krupski: FWIW... I've accidentally shorted outputs and even inserted the 328P backwards... never hurt the chip (yet).

Damaged components don't always fail immediately after being damaged.

dhenry: People screaming about "damages" here simply have no idea what they are talking about; or don't understand the datasheet when they quoted it as support.

I'm bookmarking this as a great example of "the pot calling the kettle black."

krupski:

AWOL:

Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them

You've done this?

FWIW... I've accidentally shorted outputs and even inserted the 328P backwards... never hurt the chip (yet).

I don't think you can claim that - appearing to still work is not the same as undamaged - overloading the output transistors causes local overheating and perhaps electromigration on the chip which will first degrade then disable the transistors in that area - the reliability and robustness is impaired before obvious/gross loss of function is seen. Once degraded the risk of future failure without warning is increased. Manufacturers put values in the abs max spec that are just conservative enough (they don't want to be sued for being unfit-for-purpose, yet want to look as good as possible compared to the competition... I would always recommend staying below them by a sensible margin.

Of course, in reality the datasheet specs MUST be adhered to or else the chip WILL get ruined sooner or later.

A more positive spin is obey the abs max constraints so you end up with about strange unexplaned failures in the future!

You

Most (in my experience) "newer" Microprocessors will withstand an accidental short once or twice... to ground, even occasionally instead of once or twice. Most All Microprocessors will survive a short to Vcc once or twice but likely never occasionally and No microprocessor will survive shorting to a positive supply greater than Vcc to less than ground (Negative voltages) without a resistor big enough to limit the current to what the input protection diodes can withstand. Some types of micro's are more robust than others and for some obvious reasons the choice of the Atmel product was a wise one. The '328's are a hardy chip family. I've never yet read here that shorting an "output" pin to ground will destroy that pin or the processor instantly or even soon. I've read many times of the per pin current limits and infrequently of "other" types of shorts. I've NO DOUBT that a long term short... 5 - 10 minutes would cause enough internal heating to begin the "electromigration" mentioned and even cause the device to fail. That's one major issue with mos devices and overheating from wrong type loads is the major failure event for Mosfet power transistors (Bipolar devices fail in a similar manner from "second breakdown" which is a place on the "overloaded" transistor die that has a crystalline defect, the defect gets hot and fails causing more area's near the failure to fail until the device fails utterly. If the same transistor is never operated at or above it's rated max current these types of failures are most rare. I used to test silicon power transistors for that issue by measuring the C-E resistance... it should be a near open circuit > 5 megs. Measurements less than 50K were a danger flag for me and I replaced those parts. With a mosfet there is no easy way to look for electromigration unless it be in the gate capacitance... The defect in my experience is mainly damage to the gate structure (The oxide layer under the gate metallization) and the damage is really unnoticeable until the device fails although my high power fet use was limited to RF power amplifiers. I used many power mosfets but the ones that failed were the ones that regularly were operated at 100 + Deg C (failed fans or air filters clogged). All of the above mentioned conditions are "Over the Top" and are the exception rather than the rule.... There have been a lot of "My Pin puts out 1.5V... Why? types of questions but not many in which the poster reported failure because of the error... Did I "Fry" my Uno?, I accidentally connected a pin to Vcc or ground or I connected my servo power to a pin on the Uno because I wanted to turn off the motor... but rarely reports that the device utterly failed. Common sense is the key here, A short should be avoided if at all possible but isn't cause for failure or ALL of us would be seeing more messages to that effect. Great topic for "Trolling" though... I suspect someone got stood up for "Saturday Night" and is revealing his/her frustration here...

Bob