Hi All I’m looking to detect a 230VAC signal, which is set to live when a Plumbing Valve is open. The signal line has no voltage, when the Valve is not fully open. I am thinking of using an opto-isolated detector. I want to use an 3.3v Arduino ESP32 to detect the output of the opto isolator. I…

You don't need any additional parts. Just connect it as instructed on the website

The PCB in your link has a 100kΩ resistor in the input circuitry. There is a pullup resistor R2 connected to the opto-isolator output. [s-l1600]

I can help wih code if it's simple, otherwise someone else can probably help. Have a nice day!

Be careful here: anything connected to 230VAC must be treated as mains equipment. About the resistors: Many of those “AC mains detector / opto-isolator” boards already include a series resistor/capacitor network on the input (often ~100k or a capacitive dropper). If your board has that, you do NO…

Resistors needed for opto-isolated detector?

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6v6gt January 18, 2026, 5:25pm 4

You could also look here: Mains voltage detector (neon bulb based for 230v door bell repeater)

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Resistors needed for opto-isolated detector?

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