Connect GND from different devices.

[TaurosRMK]

Hi! I use the ESP32 as an additional device to monitor my ventilation performance. I have 2 EC fans that can be controlled via a 0-10V signal (I bought a separate controller for this), and the fan RPM can be read. But I can't understand how I should do it, because on the diagram the fan manufacturer indicates that it is necessary to connect two wires FG and GND to the RPM reading device (in my case it is ESP32). But the ESP power supply is connected to another 5V power supply.

What should I do in this case, can I combine the GNDs from the two fans and the GND from the 5V power supply? Will it work and most importantly, will it not cause any damage?

I'm new to this, so I don't know all the details and I'm afraid to do something wrong.

Thanks for any answers.

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[ESP_Sprite]

You'd connect all the grounds together, and the tacho signals (which I think is what FG is) with ESP32 I/O pins. According to the manufacturers pic, you also need a resistor of 3K3 or larger from each pullup to 3.3V; I'd use 4K7 resistors for that.