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For UART transmission in a noisy environment, I am contemplating using low-cost optical TOSLINK cable with a dedicated optical transmitter and receiver, e.g PLT133 and PLR135. Is a special interface circuit needed to modulate the signal to a carrier frequency or can the optical transmitter be connected directly to the UART pin of the transmitting microcontroller?

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  • \$\begingroup\$ The transmitter datasheet says DC to 16 MHz is fine so it does not need anything. But receivers usually don't and you don't link to any receiver. \$\endgroup\$
    – Justme
    Oct 15, 2022 at 15:35
  • \$\begingroup\$ What is the reason that receivers typically don't work down to DC? \$\endgroup\$
    – mr_js
    Oct 15, 2022 at 18:31
  • \$\begingroup\$ Their internal circuitry. Receiver chips generally have some AGC and data slicing circuitry to be able to work under varying conditions, and while some can handle DC, some don't. Basically same thing as speaker and microphone. You can try to send signals down to DC with the speaker, but the microphone is incapable of receiving DC. \$\endgroup\$
    – Justme
    Oct 15, 2022 at 19:20

2 Answers 2

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The receiver needs a minimum data rate of 100 kbps. It can't receive DC, and basically UART data will not guarantee that it will work through the receiver.

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There is no need to modulate the signal - you can directly connect it to the UART. The received signal will mimic the input signal as shown on page 3 of the datasheet:

enter image description here

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  • \$\begingroup\$ For the transmitter, yes. For the receiver, definitely not. \$\endgroup\$
    – Justme
    Oct 15, 2022 at 18:14
  • \$\begingroup\$ The OP said: " I am contemplating using low-cost optical TOSLINK cable with a dedicated optical transmitter and receiver, e.g PLT133 and PLR135." \$\endgroup\$
    – ErikR
    Oct 15, 2022 at 21:13

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