Getting ready to transition from a generic NEO-6N board to the SparkFun NEO-M9N. Currently using RX and TX for communications. One thing that wasn’t clear in the documentation is the allowable logic level for the TX and RX pins. Is 5V logic allowed on those input/outputs? Currently using 5V connection to a Arduino NANO.
The product page very clearly states: 3.3V VCC and I/O.
So no, 5V is not allowed on inputs.
So a logic level converter like this one:
https://www.sparkfun.com/products/12009
is needed between the Arduino Nano TX/RX pins and the SparkFun GPS NEO M9N module but the module can be powered by 5V through either the USB-C plug or the 5V pinout. Too bad the level conversion wasn’t built in. I tend to use 5V logic devices because I power them through a USB portable battery pack.
All you really need are two resistors (1K:2K) to make a voltage divider, from the Nano Tx to the GPS Rx pin. The Nano should read the 3.3V GPS Tx signal as HIGH (it is close, but I’ve never seen it fail).