@huerta69 Can you test this with the output transistor disconnected? Replace the output with a logic probe, scope, or even a voltmeter. Frying the microcontroller indicates you're drawing too much current.

Another thought is on the power side. Did you perhaps have the XIAO connected to your computer when powering this up? That would cause issues as the 5-volt input becomes a 5-volt output, and you would be connecting two power supplies together, which usually results in bad things happening!  The solution here is a diode in series with the external 5-volt supply.

😎

Bill

I’m building a signal monitor using a XIAO ESP32-C3 microcontroller. The design includes:

• One input protected with an optocoupler
• One output driving an NPN transistor to turn on an LED
• A Hi-Link HLK-PM01 5V power supply

When I power up the PCB, the XIAO output pin gets damaged. I have carefully measured voltages and resistances without the XIAO installed, and everything appears to be normal.

So far, I have already damaged 4 microcontrollers during different tests.

Does anyone have any idea what could be causing this issue?

this is the diagram

thanks

huerta69