Arduino is not getting power from adapter or Vin

Question

Hi I am very much new to electronics, specially micro controllers and stuff. I am a Java/Android programmer by profession. I am currently creating a autonomous robot but I am stuck due to a problem.

The problem is that I have been using my Arduino UNO with a motor shield L293D this http://i.ebayimg.com/00/s/MTYwMFgxNjAw/z/70EAAOSwvzRXw-s7/$_12.JPG and a Bluetooth module HC05 Everything was good when I connected my shield to arduino, I checked my code using four extra small motors (2.5-3.7V). My arduino was functioning well with my code I was able to operate all the motors with it on my signal.

After all check when I added my all 4 motors to the shield in M1, M2, M3,M4 with my 12V battery of 1 AMP. There was sudden buzz and one IC L293D on motor shield got fried. Don't know this was because of some wire mess because wires that time not very tight and very neat. After that the gold thing on my arduino middle between USB and DC connector is getting very hot without even any usage. (I have replaced my ICs with new one). Now when I connected everything back all seems to be ok and my robot working fine but arduino last time drawing the power from the shield itself (12V battery pack). and now arduino is not taking power hence I am giving power to it from USB but I can't keep usb connected. So tried it with DC connector jack. It is not working too. Vin socket not working for power too. Ony usb is working. I also tried to connect my 9V battery to the 5V pin near Vin and it worked but after that HC05 stopped working but it is working fine with USB.

My Questions -

1. Why that gold thing is so hot (It wasn't happening earlier as per my memory).
2. Is my arduino got some problem if yes than can I solve it?
3. If arduino is really got fried what precautions shall I take to protect my next arduino.

Please help me with it. Thanks a lot.

Answer 1

I was able to solve my own problem. It was not working because in last burst my voltage regulator got burned. So when i am passing 9V to it through DC jack, it was not working. So i came to know it will work if a just pass 5V regulated voltage to it. So i just used a 5V cell to do it and then i supplied power through VIN and GND. It's working fine and the best is i didn't buy a new Arduino.

Answer 2

The trouble with bad motor wiring is that it creates an arc when suddenly disconnected and the L293D passes that excess voltage to the power rails via it's internal diodes (that's what the D stands for). This is quite normal but, if you haven't enough bulk capacitance on the power rails to soak up the energy of that "discharge" then something usually pops and, the gold thing may be that thing that popped.

That's the likely mechanism if you are interested anyway. I guess that answers question 3. Take more care with wiring next time and add some bulk capacitance to the rails. Keep wires as short as possible too.

Answer 3

That "gold thing" is a polyfuse. It is there to protect your computer's USB bus from short circuits on the UNO.

Since it is getting hot, there is a short on your UNO. One thing I see connected to USB Vcc is U2, which is a 3.3V regulator. It is also connected to the regular 5V regulator that is powered from Vin. If U2 is shorted, it will probably prevent the UNO from working at all.

USB Vcc is also connected to U3, which handles the USB communications. If it is shorted, then you won't be able to "talk" to the UNO via USB - though the UNO itself might run.