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input ac voltage range for optocoupler for zerocrossing detection circuit

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There will be always a current limiting resistor. And a diode if you don't use an optocoupler with AC input.

For general optocouplers like 4N35, 4N25, PC817, etc where the optocoupler is designed to be driven by DC, you need to rectify the 230VAC to ensure that the optocoupler gets a DC voltage. You also need to limit the current to the optocoupler using a series resistor. Calculate the series resistance as R = (Vin - Vf)/If

Remember that if you do not rectify the input using a full-wave rectifier, the opto-coupler will be off for half the cycle.

There are optocouplers that can be fed with AC input (current must obviously be limited). One such common optocoupler is TLP620.

Hope this helps.

thanks for your help and i made the circuit that detecting zerocrossing directly and it is perfectly working

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now i am going to work on developing some new protocol like uart or i2c please suggest me some helpful link

What do you mean by "developing some new protocol"? Do you want to create a completely new protocol on your own or do you plan on using or modifying existing protocols like UART or I2C?

i am going to develope my own protocol for sending 24 bit at a time yesterday i tried for its starting that through usin simulation in proteus and programmed in pic therse a lot of timming problem happening
an iam going to develope it on single wire communication

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