Electronic – arduino – How to upload code to an Arduino Nano once the custom PCB is designed and ordered

Your servo may behave erratically, and you may find that this only happens when the Arduino is plugged into certain USB ports. This is because the servo draws quite a lot of power, especially as the motor is starting up, and this sudden high demand can be enough to drop the voltage on the Arduino board, so that it resets itself.

If this happens, then you can usually cure it by adding a high value capacitor (470μF or greater) between GND and 5V on the breadboard

http://learn.adafruit.com/adafruit-arduino-lesson-14-servo-motors/if-the-servo-misbehaves

As others have commented, if your servo requires more current than the Arduino (or your USB port) can supply, you should provide a separate power connection for the servo.

Your USB port may be limited to 100mA or to 500mA, the Arduino may be able to provide slightly more current at 5V if it is connected to a power source through the barrel-jack connector. It depends on the specifications of the 5V regulator on your particular Arduino (or clone).

If you power the Arduino from a regulated 5V supply, you can draw higher currents from the V_IN socket.

I note that some retailers of your servo suggest it be used with a motor controller board.

This answer has three parts:

• What you described doing, and how that relates to elements of the Arduino design.
• What you might have done, to cause the symptoms you describe
• How you might start to narrow down the fault

What you described doing

I had connected a 12V battery pack to VIN and GND.

That is not a problem, that is the input to the inboard regulator so it's fine

I read that there's a diode on the board which selects the highest voltage in.

Yes, there is a Schottly MBR0520 diode between the USB supply and regulator output, the diode has a Vf of about 0.3v

At one point I disconnected the pack and then reconnected..
Point is, now the board wont start..

I'm not sure what to make of that, I don't see a reason for the board to get damaged

Arduino Nano schematic

What you might have inadvertently done

There's a list of ways to kill an Arduino which consists of

• Method #1: Shorting I/O Pins to Ground
• Method #2: Shorting I/O Pins to Each Other
• Method #3: Apply Overvoltage to I/O Pins
• Method #4: Apply External Vin Power Backwards
• Method #5: Apply >5V to the 5V Connector Pin
• Method #6: Apply >3.3V to the 3.3V Connector Pin
• Method #7: Short Vin to GND
• Method #8: Apply 5V External Power with Vin Load
• Method #9: Apply >13V to Reset Pin
• Method #10: Exceed Total Microcontroller Current

Number 4 and 7 are interesting candidates because, on the Nano, Vin and GND are adjacent.

If you have a Nano in a solderless breadboard, with wires connecting various IO pins to the breadboard, there is always the possibility of briefly accidentally touching a 12V power lead to some component leads that connect to an IO pin.

What you can do to narrow down the area of the fault

There are many components on the Nano board itself, by disconnecting everything else apart from power to Vin & GND you can use the schematic to work out what voltages or signals should be present at various points and use a multimeter to test whether the expected voltages or signals are present.

For example you can test the input and output pins of the 5V regulator. You'd expect to see 12V at the input and 5V at the output. If you don't get 5V at the output, you might suspect the regulator has failed. You could check it's datasheet and see what kind of protections it has.

You could also check the voltage at the reset pin of the ATmega chip. What happens when you press the reset button?

And so on.

In the end though, it isn't worth spending much time on this. Your aim is not to repair the Nano but to avoid frying another one. Reading about failure modes and taking care with connections is probably the best.