Are there alternatives for HCPL3700?
So, this is a combination of an optocoupler and a threshold circuit.
Optocouplers are probably the cheapest solution to proper isolation for anything that might be too low in frequency to pass through a capacitor. There's thousands of them, and you'll likely find many many that would suit your needs on the output side.
Threshold detectors there are plenty, and you'd need to find one that fits your use case.
So, essentially, there's nothing stopping you from building this device for yourself from a threshold detector in any form (from Zener diodes to opamp-based voltage comparators to discharge tubes to plain resistive voltage dividers) and an optocoupler. &quot;A little pricey&quot; might simply be the price other engineers are willing to pay to simplify their design.