How calculate the optocoupler circuit resistor values

Team here this is the isolated circuit while designing place random resistor values can anybody tell me how I can calculate resistor values so that this ckt work properly ( i mean it's working but I want to improve it more so that work longer or any suggestion are also welcome

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It has been moved to the General Electronics category

Consult the optocoupler data sheet for its Ic/If factor.

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If you want to optimize the design, you first need to find out what the following signals are connected to.

U3_TX
U3_RX
EXT_TX
EXT_RX

Then get the data sheets for all the ICs involved in the design and the PC817.

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You need to know the characteristics of the optocoupler
https://media.digikey.com/pdf/Data%20Sheets/Sharp%20PDFs/PC817X%20Series.pdf

and

image

Then use Kirchoffs LAws and Ohms Law.

sorry for that

okay i will then update you

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