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The Arduino due exclusively runs on 3.3V, so I am wondering if this can be used as a USB to serial converter just like the Arduino Uno could, or do you need to do level shifting?? Will I ruin the board if I just hook up RX and TX to a 5v device?

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Yes it will work as a USB to serial device, however the serial will be at 3.3V not 5V. It'll still be serial though.

For it to send data to a 5V device, depending on the device, it might work. 3.3V is often around the "high" threshold for an input pin on a 5V device, but check the datasheet for the 5V device to be sure.

For receiving data the 5V will be above the 3.3V supply voltage of the main SAM3X chip, so should be avoided. As with most Atmel datasheets, actually finding the information you want is almost impossible, and I haven't found if there is a maximum "over voltage input current" or not, so to be on the safe side a full level shifting voltage divider should be used on the RX pin.

  • According to the datasheet 'Absolute Maximum Ratings' on page 1378 (where you'd look for things like these...) Voltage on Input Pins with Respect to Ground (except VBUS)...............-0.3V to +4.0V. No idea what you mean with "over voltage input current" but I'm not surprised it isn't in the datasheet. – RJR May 11 '15 at 5:27
  • Well, I said s***w it, and went ahead and tried it. Everything actually worked just fine! I was able to communicate with a serial device with putty and send and receive commands. I probably am going over recommended voltage, but I have not fried my Arduino (checked Rx and Tx with 3.3v device afterwards), so I guess it's fine. – John August May 11 '15 at 15:34
  • The "over voltage input current" is basically the current rating of the ESD diodes on the input pin. I fyou know that you can get away with just a series resistor on the RX pin to protect it. I would advocate at least having a series resistor if you are reticent to make a voltage divider. 1K would most likely give enough protection. – Majenko May 11 '15 at 16:33

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