If possible, what are calculations and precautions involved in making a simple transformer without core? The only purpose of this transformer is to trigger an opto-coupler for zero-crossing detection of mains supply.
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Best Answer
Since you said that it didn't need to be isolated, maybe something like this would work:
Output looks like this:
If you are on 120Vac, then change the 2.2k to ~1.1k.
Again, beware that the left hand side is not isolated from the mains.
Source: https://circuitdigest.com/electronic-circuits/zero-crossing-detector-circuit-diagram