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I have no experience about serial communications, with that being said; I have two circuits isolated from each other and each have a ATMEGA8 reading a voltage on their ADC.

I want one of them to send ADC data to another without having a common ground. I know that I can do it with a Bluetooth or Wi-Fi "module" but I'm looking for an easier way, like maybe with an optocoupler but again I'm not aware of the limits.

  • What's the cheapest and simplest way to do this? and basically how it's done?

There's a lot of information about making two Arduinos talk to each other but I couldn't find much information/documentation on isolated communications.

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    So you still want communication via a wire, but just with isolated grounds? Then yes, the optocoupler is the correct way, one for each UART/Serial line. You can find tutorials on how to use an optocoupler on the web. Do you have any specific questions about it?
    – chrisl
    Aug 12 at 20:14
  • @chrisl I'm not lazy, I just couldn't find it. can you please link one of those tutorials on how to use optocouplers for serial communications? Aug 12 at 20:15
  • I didn't want to suggest, that you are lazy. I would suggest to read a generic tutorial about optocouplers, not directly involved with UART/Serial. They are pretty simple components, so the general principle is also how they are used for Serial. When you understand how they work and how they are wired you should be able to build them into your Serial path. I guess you searched for tutorials directly with the Serial lines, but there are many tutorials when searching only for optocoupler tutorials.
    – chrisl
    Aug 12 at 20:39
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    A few seconds on google images looking for "optoisolator uart" yields a number of possible circuits.
    – Majenko
    Aug 13 at 10:36
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    One example: github.com/TaaraLabs/OptoIsolatorFTDI/blob/master/…
    – Majenko
    Aug 13 at 10:37
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[Consolidating an answer from the comments]

A wired connection using Optical isolation (aka Optocouplers) is the recommended way to solve this problem.

There are tutorials available online regarding optical isolation (e.g., https://www.electronics-tutorials.ws/blog/optocoupler.html; https://bestengineeringprojects.com/interfacing-optocoupler-with-arduino/).

One (of many) possible example circuit was noted as: OptoIsolator FTDI Circuit

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    Note that, on this schematic, the pin labeled “RXI” on the left should be connected to one Arduino's TX, whereas the “RXI” on the right should be connected to the other Arduino's RX. Aug 14 at 17:30

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