Alright bear with me since English is not my first language and it's my first time posting here.
So I was using my Arduino Nano (not genuine) to drive a single phase full bridge rectifier. The Arduino itself was being powered by an USB wall adapter. I used the 5V pin of the Arduino to power a 16x2 LCD and a LM358 Op Amp.
The LM358 also used an external -5V power supply since I was using it as a zero crossing detector for the sine wave. The 110V sine wave came from the mains to a 1:1 isolation transformer then to voltage divider to get a 5 V wave and then into the non inverting input of the Op Amp.
The SCRs where being triggered by the Arduino trough 4 MOC3023 optoisolators and a Snubber circuit. The Arduino, -5 V power supply and the 110 V sine wave all shared the same ground.
Everything was working fine until randomly, the -5V and 110 V ground cables got disconnected from my breadboard and the Arduino died.
The CH340C and ATmega328 chips get really hot now so I assume they are the ones who took the hit.
My question is, what could've caused the damage? and what can I do to avoid it?