Connected the 3.3v output and the 5v output together

Question

I accidentally connected the 3.3V output and 5V output to the same connection. How bad is that and what issues could that cause?

I was busy with making my first project which uses a module which runs on 3.3V and all other logic and LCD screen and such which run on the 5V. When rearranging, I put both of the outputs on the same part of the circuit.

Luckily it all still seems to work but I am quite curious what issues this could cause to both the components and the Arduino.

Added a very basic version of the schematic as I don't have a good software for that yet. Left out all stuff not connected to the problem of the circuit.

Schematic diagram

• Greenonline: Which outputs? Which pins? Do you have a schematic showing where the short was?
• R.vW: Have added a schematic, hope this clarifies my question. Also, the question more meant as I know I should not do it but what is exactly going wrong when combining both of the voltage pins.

Answer 1

The 3.3v parts are the more likely to suffer, as the accidental connection presented it with an overvoltage - 5v, where it expected only 3.3v.

If that part or parts doesn't present a short-circuit or almost short-circuit, the nano's power-supply is probably tolerant enough to survive it. But your DVM is your friend; power up the nano by itself (nothing external connected to it) and test the +5v and +3.3v outputs. If they still present the right voltages your nano is probably still healthy.

Answer 2

It depends on what else was connected and if the power supply shutdown.

Whatever was connected to the 3.3V line at that moment is likely damaged. The term used is "walking wounded". Things may appear to work fine abut may fail later. There is no way of predicting.

Just keep that in mind if you detect any unexplained issues later on.