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Topic: Serial communication between 3.3V board and 5v board (Read 161 times) previous topic - next topic

probierer

So I have an Arduino Mkr zero and it should send commands to an arduino nano! I know that the mkr Zero isnt 5V tolerant. This isnt a problem because I only need one way communication (The mkr zero doesnt need to receive commands). But I am wodering if it could still be damaged by voltage spikes from the nano on startup or something else. So my question is if the arduino nano will only have 5v on a pin if defined as output and set to high in the programm? Or can there be other situations when 5v is emited from a pin that could possibly damage my mkr zero?

Paul__B

Just put a 10k resistor in series, mounted directly adjacent to the Nano.  However if you are using the hardware UART - pin zero - then the USB-serial chip connected through a 1k resistor will prevent this from working (and could cause some problems anyway).

Probably just a Schottky diode from the output pin of the Zero to the 3.3 V pin.

probierer

Okay thanks for the Info!  Just to get it correct: You said that the hardware uart is pin zero but when I look at the pinout from the mkr zero: [iurl=https://content.arduino.cc/assets/Pinout-MKRZERO_latest.png]pinout[/iurl] . It looks like pin 13 and 14 are for uart. Is pin 14 safe for use with 1k resistor or not? 

And for the Schottky diode why should I connect it to the 3.3v pin?


Paul__B

Sorry, I was thinking of the UNO/ Nano with the ATmega328.  :smiley-roll:

Haven't looked at how the Mkr Zero is configured.

The Schottky diode from an input to 3.3 V ensures that the pin cannot be pulled significantly above the supply rail whether that supply rail is powered or not, so protects the internal protection diode in the microcontroller from excessive current.

probierer

Okay thank you for the Informations! 

I have on elast question just for my understanding! Why can't I put an diode (Maybe signal diode) between mkr zero and nano to protect it from voltage going in the wrong direction?

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