Phone ring detector circuit needed

[jack0987]

The circuit will work with just about any "standard" optocoupler. The 4N35 is just one I grabbed from the design library. The 4N33 should be no problem. Again, it has so much gain that input resistors R1 and R2 can be increased to 100 K.

The 2N7000 is nice because it does not require an input resistor. It can be replaced with any NPN small signal transistor such as 2N2222, 3904, 4401, etc. For these, add a base resistor that yields a base current of 2 mA - ish. This will work well for any LED current up to 30 mA. The standard rule of thumb indicates a max collector current of 20 mA (10x the base current), but that is for transistors designed in the 1950's.

ak

Thanks so much. I have decided to build your design.