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[on:]

Hello,
  I am using external 12V DC source with Arduino Mega2650 R3 to use 5V output to drive stepper motors. It has been working fine till now. Arduino micro seems to be working find but the problem is that I cannot connect to the board via USB anymore. I have discovered that the regulator output gets to 8V instead of 5V and this voltage is being applied to micros which get over temperature. May them have been damaged? How can I test it? The fact is that when I just use USB power board seems to run ok except for not being able to communicate with it...
  The board is running the sw as programmed but I can not connect to it anymore. I have tried to get into DFU mode to flash the 16U2 with the firmware but I have not found references on how to do this with this board...(found many for others) How to get into DFU mode? How to know it is this mode? Atmel flip sw always says  disconnected...

  Any help on this is appreciated!

  Thanks and rgds,
Jaime.

[Reply #1 on:]

The USB micro is dead for sure, and the main Atmel is damaged - unless you have access to SMD rework equipment and can replace the chips, bin the board and get a new one.

I wouldn't just replace the USB chip and hope for the best.

// Per.

[Reply #2 on:]

I am using external 12V DC source with Arduino Mega2650 R3 to use 5V output to drive stepper motors.

Were you using the 5V pin on the Arduino power header to power the steppers? If so, you
almost certainly cooked the 5V v.reg on the board, and sounds like it failed and blew the
entire board.

That's the Achilles Heel with buying expensive boards that have all tiny surface-mount
components, and next to zero protection for overstressing anything. When the board is
toast, the board is toast. Fixing anything smt is almost hopeless.

I think I'd buy a cheaper board with parts that can be replaced [ie, something "without"
an R3 sticker], and be sure "not" to use the 5V header pin to power external devices.

[Reply #3 on:]

I think I'd buy a cheaper board with parts that can be replaced [ie, something "without"
an R3 sticker]

The r3 atmega328 isn't surface mount: http://arduino.cc/en/Main/ArduinoBoardUno and the usb-serial chip has always been surface mount.

[Reply #4 on:]

Yeah, I wasn't very clear, was I. It's just my opinion, of course, but I think things are
going in the wrong direction. Too many tiny smt parts, too little protection on I/O pins,
v.regs way too small physically, use of ceramic resonators on the main processors instead
of crystals, inability to even remotely fix blown boards. And mainly for products meant
for use by lots of noobees. I can probably think of a couple more. But, it's only my
opinion.

[Reply #5 on:]

Hello,

 Thank you very much for your comments. A silly question (sorry but not an electronics expert). My understanding is that the SMD voltage regulator within Arduino Mega ( NCP1117ST50T3G) drives up to 1A. The stepper motor I am connecting needs much lower current - why this may makes the voltage regulator fail?

  In any case for sure next time I will use external voltage regulation circuitry to avoid this happening again.

  Best regards,
Jaime.

[Reply #6 on:]

The currents you see, are (let's say) an average.
A motor needs a lot more current to start (like 6 times that average).
A stepper motor gets powered, steps (hence the name), and then has to be powered in another way to make the next step.
So it has a lot more starts, since every step is (almost)a new start.
Every time you are powering an inductor (which a motor is), the current will be quite high, and every time you stop powering that inductor, a reverse power pulse will be generated from that inductor.
All this will add to the load, and you're supposed to build a filter to get rid of this (a motor shield is supposed to have that).
The power supply of your Arduino board is meant for the Arduino board itself, and has some reserve for some small external loads.
I wouldn't use that supply for stuff like motors, an external power supply with adequate filtering will save your Arduino board from frying.

[Reply #7 on:]

Hello,

My understanding is that the SMD voltage regulator within Arduino Mega ( NCP1117ST50T3G) drives up to 1A. The stepper motor I am connecting needs much lower current - why this may makes the voltage regulator fail?

  In any case for sure next time I will use external voltage regulation circuitry to avoid this happening again.

  Best regards,
Jaime.

When you are powering the voltage regulator with 12V and drawing 1A from it, the voltage regulator has to dissipate 7W of heat (1A x 7V = 7W). The tiny voltage regulator only has the PCB to dissipate the heat, 7W of heat is a lot. There is no way that it can handle it and you will damage it. An Arduino can control a lot of things but not power them, certainly not motors. It is not made for that. I would never draw more then 200-300mA from the onboard regulator.

[Reply #8 on:]

Hello,

My understanding is that the SMD voltage regulator within Arduino Mega ( NCP1117ST50T3G) drives up to 1A. The stepper motor I am connecting needs much lower current - why this may makes the voltage regulator fail?

  In any case for sure next time I will use external voltage regulation circuitry to avoid this happening again.

  Best regards,
Jaime.

When you are powering the voltage regulator with 12V and drawing 1A from it, the voltage regulator has to dissipate 7W of heat (1A x 7V = 7W). The tiny voltage regulator only has the PCB to dissipate the heat, 7W of heat is a lot. There is no way that it can handle it and you will damage it. An Arduino can control a lot of things but not power them, certainly not motors. It is not made for that. I would never draw more then 200-300mA from the onboard regulator.

I agree with you on limiting use of the 5V pin to 200-300 ma. However the popular notion that one can damage the regulator from over current or over temperature, while a widely held view, goes against every linear voltage regulator datasheet I've ever come across. They all seem to have internal auto protection circuit that shuts down the output upon over temperature or over current draw. So saying that will damage the regulator goes against the manufactures designed protection. That is not to say that there is not ways to damage a linear regulator say by over voltage on the input or reverse current from output to input.

From a typical datasheet:  ( http://www.fairchildsemi.com/ds/LM/LM7805.pdf )

• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection

Lefty

[Reply #9 on:]

From a typical datasheet:  ( http://www.fairchildsemi.com/ds/LM/LM7805.pdf )

• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection

So, with all that protection, why did the regulator fail?

[Reply #10 on:]

From a typical datasheet:  ( http://www.fairchildsemi.com/ds/LM/LM7805.pdf )

• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection

So, with all that protection, why did the regulator fail?

Because the failure mechanism was of some other nature? What that might be I have no way of telling but I did list that too high a input voltage or having reverse current flow through a regulator can be destructive to the chip.

Do you not believe what the manufactures datasheet says about their chips when they talk of built in protection features?

Lefty

[Reply #11 on:]

OK. There are other reasons for the fail:
1) Unlucky.
2) Angered the transistor gods.
3) Failed to pay protection to the local mafia.

I use built-in protection features on my electronics. They are called fuses. However, when they protect my devices best, they also throw themselves on the grenade.

Arduino micro seems to be working find but the problem is that I cannot connect to the board via USB anymore.

This sounds familiar to me. IC7. But that is just me...
((Vin > 10v) && (usbPower == true))

[Reply #12 on:]

Possibly, the inductive spikes from the stepper motor switching blew the v.reg or
other circuitry. This is why it's always good to use a separate power supply for such
loads. Another likely possibility is accidentally touching 12V to a pin on a 5V part
- easy to do.

Also, for best results, on the power input to the stepper motors, you will want to add
both bypass [0.1 uF] and reservoir [100 uF or more] capacitors at the point where the
external supply connects to the motor driver board, in order to filter motor noise, etc.
You want his whether you're using steppers, regular motors, or servos. They all
generate a lot of electrical noise.

A silly question (sorry but not an electronics expert). My understanding is that
the SMD voltage regulator within Arduino Mega ( NCP1117ST50T3G) drives up to 1A.

Everything the other guys said about overheating the tiny smt v.regs is true. With 12V
for Vin, you can only realistically provide 100-200 mA of load current at 5V without
heating problems.

The question is not silly at all, because the overheating issue is not to be part of the general
info provided in adverts, so it comes up on this forum a couple of times every week, and
has to be explained again and again.