I developed a PCB for a project I'm working on. Today after assembling I tested everything and all relays where working as well as the ESP32 itself. Then I connected the sensors and it stopped booting.
After rolling out the problematic sensor I found that a water sensor that works like a button stops the ESP32 from booting when plugged in when I connect the power, but if I connect the sensor after the ESP32 has booted it works fine.
As a side note: I also noticed that the ESP32 was getting hotter, but not overheating at all, just a bit more warm than I would say normal.
Here is the schematic (VCC = +5 VDC):
The sensor:
I'm using pin 25 for the sensor and from online research I found that pin 25 should be OK for anything and technically shouldn't interfere with the boot up.
In the schematic I had a pull-down resistor of 1 kΩ; I also tried using a 10 kΩ resistor, but no luck.
I tried removing the pull-down resistor altogether and also tried activating the internal pull-down resistor of the ESP32 using software, but still no luck.
I'm using a Raspberry power supply, so 3 A at 5 V, and using a multimeter at the 5 V pin on the ESP32 shows around 6 V being received by it, so I think I can rule out the internal diode voltage drop that some boards have.
Also tried a 10 kΩ pull-up resistor between GPIO0 and 3.3 V but that didn't do anything either.
Best Answer
If VCC is 5V, then you are exceeding absolute maximum ratings for the input pin.
ESP32 does not tolerate 5V on IO pins. It may go into latch-up so it may recover, or get damaged permanently.
Don't feed overvoltages to IO pins.