Will putting in a wire into the Arduino after the sketch is uploaded damage it?

Sorry about the super nooby question.

But I got the infamous ‘avrdude: stk500_getsync(): not in sync: resp=0x00’ error when uploading and I did all of the usual things change serial ports, update drivers, etc…

I seen somewhere if you don’t put a wire into the RX pin until after the sketch has uploaded it fixes it, and it did!

This then got me thinking, just like the title suggest will this damage the Arduino in anyway if I keep doing it?


Pins 0 and 1 are kinda special; they are used for communication to the PC via the USB interface. As such, if you have a sketch that needs to communicate with the PC, you can't hook anything to them. This also includes when you are loading a sketch, as you've found. After your sketch is loaded, you can hook up whatever you need to those pins. Typically, people avoid using those pins unless no communication with the PC is needed by the sketch and there aren't any other pins to spare (or any other way to gain more I/O pins for the task).

With that said, I do want to leave you with this caution: You should never plug or unplug wires in a live circuit. This includes your Arduino when it has power going to it. I can't tell you the number I times over the past few years I have read of somebody frying their Arduino because they simply bumped a wire, let alone moved it (letting it touch the wrong pin or such). Ideally, you should remove all power from the system, make your changes, double check them, triple check them, then go away for a bit, come back and quadruple check them - to make sure that what you have changed is -exactly- right, before you re-apply power.

This goes especially for running tests with a multimeter or other piece of test equipment. You should -never- move probes around on a live circuit if you can avoid it. If you can't - move only a -single- probe, and keep your other hand away from the device under test (this is called the "hand-in-pocket" rule - can you guess why?). The idea is that you have less of a chance to slip with a single probe, avoiding damage to the circuit under test and/or the testing tool as well - not to mention yourself (this applies doubly if the device under test is a high-voltage or high-current device; one slip there with both hands or one hand in the wrong area, and you could get shocked, with the voltage going right across your heart, potentially stopping it).

Get into this habit -today- and you may thank me for it years down the line (when you slip, blowing a capacitor or frying a test lead or something - generally with a loud bang, some smoke, and maybe some fire - but at least you'll be alive).

I seen somewhere if you don't put a wire into the RX pin until after the sketch has uploaded it fixes it, and it did!

Under the circumstances though, as described here, it can be unavoidable. I personally add and remove wires from live circuits but I usually do it after double-checking I got the right pin. Shoving something into +5V when you meant Gnd, or the wrong digital or analog pin could indeed damage things.

But with caution (and anti-static precautions) I think it is OK.

Although as cr0sh pointed out, you could upload, disconnect power, rewire, and reconnect power.