Urgent - TX/RX with RPi

Hello all,

This may be a stupid question, but I could not find an answer to it yet:

I am sending data from an Arduino Uno to be read by a RPi 2b through serial communication between the TX/RX pins of both boards.

I will not need to send data from the RPi to Arduino, thus, would it be safe to assume that I only need to connect the TX from Arduino to the RX of RPi?

I am following this tutorial: Arduino and Raspberry Pi Serial Communication | Code and Life

And it seems that the RX in Arduino is held at 5V sometimes; since I do not need to read anything from Arduino, it seemed as only logic to simply not connect it. Would this work?

Thank you.

Always connect the grounds together.

Do not connect 5 volt signals to RPi inputs without using a 5V-3.3V level converter. You will damage the RPi.

Hi jremington,

Thanks for the answer.

Indeed that would be the best, however I do not have one at hands right now, neither the time to wait. Thus, I would like to do a simple voltage divider, which has been proven to work between the TX Arduino and RX of the RPi without causing any damage; the thing is, the same is not applicable to the RX Arduino and the TX of the RPi. Thus, I would like to know wether the TX/RX communication would still work even if I leave the RX Arduino / TX RPi cable unplugged.

viraseres:
Hi jremington,

Thanks for the answer.

Indeed that would be the best, however I do not have one at hands right now, neither the time to wait. Thus, I would like to do a simple voltage divider, which has been proven to work between the TX Arduino and RX of the RPi without causing any damage; the thing is, the same is not applicable to the RX Arduino and the TX of the RPi. Thus, I would like to know wether the TX/RX communication would still work even if I leave the RX Arduino / TX RPi cable unplugged.

As long as you put the voltage divider on the UNO.tx->RPi.rx and connect ground you can send from the Arduino to the Pi.

Chuck.

Voltage dividers are fine in that case.

3.3V signal levels are usually recognized as a valid HIGH by a 5 V Arduino, so you can connect an RPi TX serial output to an Arduino RX input without problems.

However, it is a good idea to have a series resistor (say 10K) between them to avoid damage, in situations where one or the other device is unpowered, or the 5V Arduino I/O pin inadvertently becomes output and HIGH.