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Connect Arduino Uno RX/TX to 3.3v NEO-M8N gps module

I'd like to connect an M8N gps module to an Arduino Uno. From what I understand

  • the Arduino pins 0-RX/1-TX work on 5V
  • the M8N RX/TX work on 3.3v
  • the sensor-TX sending to the Arduino-RX should work (3.3v is "good enough" to drive the Arduino-RX-pin)
  • the Arduino-TX sending to the sensor-RX is problematic because of the 5v (could break the sensor)
  • During USB-programming, the Arduino-RX sensor can be at 5v (so suddenly the current flows in the "wrong direction"- which could break the sensor)
  • A level-converter could be used to "translate" the voltages in each direction.

Assuming we don’t use a level-convertor

  • Could we use a schottky-diode (which as I understand blocks current in 1 direction) to block the 5V from the ArduinoRX going into the sensor?

  • But then the 3.3V from the sensor-TX would pass (correct direction ), but the diode will drop the voltage "a bit more"... is this still enough to drive the arduino RX-pin?

  • And it works, why not also use a schottky-diode to also protect the Arduino-TX to sensor-RX connection ( just to be safe, since some people were saying one some Arduino they needed to connect RX-RX and TX-TX to get the communication to work.. ? ).

As an alternative to the schottky ( or maybe in addition to it) - Could we simply take 2 voltage dividers (for one for both RX-TX and TX-RX) ?

We can use a "resistive voltage divider" to lower the Arduino-TX 5v to 3.3 V - I understand to get from 5V to 3.3V we need "x" and "2 * x" resistors-values, so e.g 1K Ohm and 2K Ohm... but how do I know which values would be appropriate ( I mean, we could also take 10K Ohm and 20K Ohm, would also lead to 5V to 3.3v) but at a different current (Amps)... ?

Please be patient, electronics-beginner here trying to make sense of this...

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  • How can it be that RX is driven ... ? It's an 'R' port and as I suggest it stands for Receive. So wouldn't it be that the TX 3v3 port is driving the RX 5V so the RX 5V needs a pull-up? The whole thing does not make any sense this way (for me). Commented Nov 18, 2022 at 11:40
  • UART Rx ports idle high. This means there is a high probability the Rx pin will contain pullup to 5V. So not actively driven but a passive low strength pull to an excessive voltage. The protection diodes internal to the 3.3V part could probably cope with that, especially if there is a series resistor, but this reduces the strain on the 3.3v part. Commented Mar 22, 2023 at 14:19

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