# just had an Arduino UNO bootloader replacement. Computer still won't recognize it

Before I get any thumb-downs, I would like to mention that I have read all the questions posted regarding the issue I have, but none of them had a working answer to my problem. Here's my problem: I have recently plugged in an DC motor directly to my Arduino UNO, and it resulted in the atmega328p being completely fried. So, I went ahead and purchased a new ATMEGA328P-PU and replaced it with the toast one. The computer, however, still won't recognize my chip. My questions are: Why is my microcontroller not being recognized? Is there a chance that what I've done have completely fried the microcontroller, not only the bootloader?

Things I have tried/observed: I have noticed that the new bootloader blinks the 'L' LED. My assumption here is that the bootloader comes pre-compiled with the 'Blink' project. I own 7 computers (with the three major OSs on them). None of my computers was able to recognize the microcontroller (so at least now I know it's not an issue with the USB connection).

I am considering buying a new Arduino UNO, but before I do so, I really need to know what exactly is wrong with this one, just to avoid encountering similar issues in the future.

I know I'm desperate and slightly out of options when I end up posting on stackoverflow. So, I'd highly appreciate any contribution to solve my problem.

• What is an SD motor? Is there a chip on your UNO near the USB interface labeled FT232 or something similar? – jippie Jul 13 '13 at 19:03
• How do you "fry a bootloader"? A bootloader is software. If your arduino is damaged, it probably means that your motor overloaded a port, and that may render the board unusable. How much current does your motor draw? Did you use a diode across it to prevent high voltage buildup when the power to it was removed? – user2019047 Jul 13 '13 at 20:48
• @jippie, I'm sorry, I was in a hurry when I typed my question. I misspelled the word 'DC.' – Fadi Hanna AL-Kass Jul 13 '13 at 23:15
• @user2019047, by bootloader, I meant to refer to the ATMEGA328P. The DC motor I connected required 5V to function. and yes, I did use a diode – Fadi Hanna AL-Kass Jul 13 '13 at 23:19

Just to clarify, you purchased an ATMega328P microcontroller with the Ardunio Bootloader already programmed into it? if that is the case, it sounds like the ATMega16u2 interfacce chip on your uno is bad. Its sits between the usb connection and the AtMega328 and convert usb signals to TX and RX serial data onto pins 2 and 2.

You could measure your 5v on the board and make sure its still good. If its good, its probably a bad board. The 5V may have gotten a spike from the motor.

• Yes, the ATMega328P I purchased is pre-loaded with Arduino Bootloader (or at least that's what it claims). I did check both the 3.3V and the 5V, and they're both good. So I guess the only option I have is to order a new board? – Fadi Hanna AL-Kass Jul 13 '13 at 23:32
• Did you try a different USB cable? Other than that, sounds like the best option is a new board. Hang onto the old one though, it might be programmable by connecting TX and RX from the old one to the new and removing the ATMega328 in the new one. The old one may have to be modified though to phyically disconnect the 16u2. – BrianK Jul 14 '13 at 3:25
• The old board also should be programmable through SPI, either with another Arduino (using ArduinoISP or ScratchMonkey) or a dedicated AVR ISP programmer. If that works, the old board may still be usable for any project that does not require serial communication. – microtherion Jul 14 '13 at 3:30

Reading the Arduino UNO schematic as per another answer it's likely that the ATMega16U2 that provides the USB interface has been damaged. Looking at the way the two devices are connected there is a 1K resistor in series with the serial lines that has probably limited the current enough for the internal protection diodes to protect those lines.

Given that I'd say most likely what has fried the second microcontroller is a spike on the +5V net. If that was the case another component I can see that may have been damaged is the op-amp U5 that among other things helps switch between external and USB power. It may be worth trying to program the board with external power applied if you're not doing that already, but if the spike was large enough to damage the op-amp it's probably damaged the micro as well.

More realistically though there are some other components such as crystals and capacitors that may have been totally or partially be damaged so you'll probably save yourself some grief in the long term by getting a whole new replacement board. Hang onto the new chip for a future project, there's no particular reason to think the new one would have been damaged.