Integration with an electric gate control board issue

Hi Guys, I’m a bit stuck on a problem, I want to use a photon to monitor the conditions of an electric gate control board. Note there are two different types of contact I want to monitor safety I.e photo calls (N/C contact) and triggers I.e open commands (N/O contacts).
The gate control board uses 24-30vdc across these contacts and is looking for the voltage to be pulled down, so if the contact is closed the voltage is pulled down if it’s open then is high.
My problem is as soon as I try and wire any type of circuit into these terminal it has an affect.

Any ideas how I can get a photon to just site snooping on the state of the contacts without affecting them. The control board in question is a BFT Thalia L.

Thanks in advance for any and all help and guidance.

You won’t be able to connect these inputs directly to the photon, that voltage will fry your pins. You will need some kind of intermediary, like a relay, except that any gate operator board does not have the amperage on those terminals to power a relay.

Depending on the model of photo beam, there may be a secondary output from its relay, you could use that. As far as the trigger (I’m assuming you mean open command), you will probably have to set up a secondary device like a reed switch to indicate when the gate opens.

A trick I have used is to connect a voltage regulator IC ( that can handle the 30VDC) to the high side of the relay (measure with a meter to see which one) and that outputs 3V3. Then connect the 3V3 via a 100R resistor to the digital IO.

Something like this

Easy and quick and takes almost no current from the terminals.

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Thank you both for your good advice, I will start investigating and bench testing voltage regulators.