5 ms·

I don't think price is significant factor. It just needs optocoupler, diode and few passives.

• klodolph 6y ago
  You don’t need an optocoupler to measure grid frequency. You can just use a resistor. Dirt cheap, cheaper than a crystal.
  • garaetjjte 6y ago
    Yes, but OP talked about isolated circuits. It's likely that most appliances don't need to be isolated though.
    • klodolph 6y ago
      OP was talking about consumer circuits, I think they were mistaken about how likely they are to be isolated.