Any opto isolator will work as long as you know the pin assignment. The question is rather if it will fit whatever you plan to measure. There are OI of different sizes and shapes.
"TTL to RS232 adaptor Explained
How to build a simple TTL to RS232 adaptor for your microcontroller projects. You should be able to scrounge all the parts you need or buy them at your local Radio Shack. In this article I explain how the adaptor works and provide many links to more information you need to know as a microcontroller hobbyist. This article should be very helpful to those that receive the free Arduino compatible kit offered by uC hobby as part of the Arduino Microcontroller kit giveaway.
Just about every microcontroller available today includes at lest one UART or serial port. Serial ports are the most common way to communicate with a uC or other devices such as GPS receivers. The most common interface type is RS232, only a simple conversion from the logic level signals of the uC serial RX and TX pins is required to work with RS232.
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