I think I burned my arduino

Using Arduino Project Guidance
1

Hi,

I think I burned my arduino nano cause when I connect it to my computer (USB) with nothing else connected to my arduino, the FTDI chip gets really hot.

I just wanna know what I did wrong and I think I may have an answer but I would like your expertise into this:

  1. my arduino nano was being powered by the VIN pin using a 12v power supply. I connected a servo to the power supply (it's a 12v servo) and as I see I connected the VCC lead of my servo to the same wire that was connected to VIN at my arduino so they all share a common 12v;

  2. everything was working fine. So I needed to debug my code and I also connected my arduino nano to my USB port so I could see the data in the serial (coming from arduino to pc);

  3. everything was working fine. So I disconnected the 12v power supply from my arduino VIN pin (which was soldered to the VCC lead of my servo) leaving only USB connected. When I did this I heard a PLOK noise and arduino wouldnt work anymore.

So I ask you: when I am powering arduino using USB and I have a servo connected to VIN pin of arduino, can it damage arduino? I mean, powering arduino using USB should make VIN 0v right?

2

so, you are saying you tried to power your 12v servo from the v-in pin?

3

I mean, powering arduino using USB should make VIN 0v right?

Wrong.

If you have a load on that Vin ( like your servo ) then you will draw current backwards through the voltage regulator and the MBR0520 series diode. Therefore producing as you say PLOK.

It looks like you might have blown this diode rather anything more complex.

4

All inductive loads (servos, coils of any kind, steppers, dc motors etc.) cause a "back voltage" and thus a current backflow, when you are opening an active circuit.
That's why you always should power everything down before you disconnect inductive loads.

5

did you try connecting 5 volts to the 5v line ? pin 4

if you did pop the diode, as is most common, the unit is still working fine. you need to replace the diode.
alas, the cost of these now makes a new one easier for those that don't solder smd parts.

6

I think @Grumpy_Mike is the one who came close to the answer. I think @Grumpy_Mike was the only one who understood what happened and I think he is right.

@Grumpy_Mike you are saying that when I am not powering my arduino using VIN (but using only USB) the current can go from the arduino to the servo burning arduino (which cant handle all that current)?

Please check the image here Imgur: The magic of the Internet

Indeed Grumpy_Mike is correct, so how can I solve this problem? Could I connect a DIODE going from the VIN pin (from arduino) to the SERVO/BATTERY? So this way this pin will only accept INCOMING current and not outgoing current? Could I be safe this way?

7

Could I connect a DIODE going from the VIN pin (from arduino) to the SERVO/BATTERY?

Yes, cathode to Vin and anode to battery.
A diode like this is already fitted in the Uno but it is not in the nano.

8

@Grumpy_Mike are you sure in UNO there is already a diode at vin? Cause I pretty sure I already used the VIN pin from UNO to power it and also to drag power it to do other things. If there was a DIODE in VIN pin of UNO one of those things I couldnt do, correct? Cause diode only allows current to flow one direction...

9

does not sound like the same problems with power.

10

arrozfeijao:
@Grumpy_Mike are you sure in UNO there is already a diode at vin?

Check the schematic for yourself and see.