ESP32 board won't boot when hooked to optocoupler

ESPHome
1

I have an ESP32 connected to two 12V → 5v 8 channel optocouplers. I’m connecting the optocouplers to the ESP32 using GPIO pins 5, 12-14, 16-19, 21-23, 25-27, &32-33 plus the GND and 5V.

The ESP32 will not boot if I have 12V power going into the receiving side of the optocoupler. I’ve reviewed the ESPhome documentation on what pins have special functions, but none of the pins I’m using are mentioned, with the exception of 32&33 which just lists that they can measure voltage.

Is there a pin I’m using that I can change to a different one to get the ESP32 to boot regardless of the state of the optocoupler?

2

Hi
I dont know what actual board.
But according to this esp32 board.

if GPIO12 is HIGH then it fails to boot.

So I suggest that you check the actual board you have.
But try to disconnect gpio12 as start maybe.

/Mattias

3

Thanks for the help.

I tried moving the high input wire from GPIO12 to GPIO35 and then GPIO04. Neither solved the problem. When I get some more time I’ll try disconnecting each wire one at a time to figure it out.

4

Sorry that I could not help you more.

But try to start to connect one. So It is not electrical due to some connection that should not be there.
Good luck and hope you find the cause.

/Mattias

5

You shouldn’t be putting 5v into the esp32. They are 3v3 devices.

6

Well shoot, maybe that’s my issue. I figured since the relays I use with the ESP32 are 5v that the optoisolator could be too.

7

I’m getting 4.3v at the output of my optoisolator. Is that enough to cause problems with the ESP32?

8

Yes. I believe it’s 3.5 volt that is the upper limit