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I'm using the HC-05 Bluetooth module but I'm confused about the TX,RX pins. I want to know when should I connect the RX to a divider circuit to convert 5v to 3.3v. Because while searching, I saw both of the following:

  1. either RX is connected to TX of the UNO and TX is connected to RX of the UNO without a divider circuit.
  2. or RX is connected to a divider circuit and then connected to any digital pin , TX is connected to any digital pin as well.

So can you give me a thought about both the situations? my thought is that only digital pins needs a divider rule, but the TX,RX pins can be connected directly and operates without any problems but if so, then what's the difference between both?? Note that I'm using HC-05 to turn on a LED. Hope to see some good explanation that suits a new Arduino learner. Thank you..

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You need a logic level translator of some form (such as a resistive divider) if the Arduino runs at 5V. If it's a 3.3V Arduino then you don't need one since the logic levels will match.

You connect to the TX and RX pins (or TX1/RX1 etc) of the Arduino if you want to use a hardware UART (Serial, Serial1, etc). You connect to any pins you like (with certain exceptions for the Mega) if you use SoftwareSerial instead of a hardware UART.

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While you should use a voltage divider on the Arduino TX --> BT RX signal, you honestly don't need to. Many people, including myself, have used HC-05s without voltage dividers and haven't let "the magic smoke" out of the device. Adding a voltage divider may, though, may increase the lifespan of the HC-05.

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