Pro Micro as USB to UART

I bought a 3.3V Pro Micro. I have a Skytraq GPS device that communicates via 3.3V UART that i have connected to pins 0 and 1 of the Micro. Im trying to use the Micro as a USB to UART hub.

void setup() {
   Serial1.begin(115200); // Init Hardware Serial port on pins 0 and 1
   Serial.begin(115200);  // Init Serial Port

void loop() {
  if (Serial.available()) {
  if (Serial1.available()) {

Im not sure why this wouldn't work? The GPS receiver works perfectly with a FTDI USB to Serial adapter.

Have you a GND connection between the Micro and the GPS?


Yes. The GPS module is getting 3.3V and GND from the Pro Micro. It works with my Teensy 3.2 using the exact same wiring and code. Maybe it's something to do with the 32U4?

Now that you say it works with your Teensy I wonder if the difference is due to the ProMicro being much slower. Would it work at a lower baud rate?

Alternatively it may be worth receiving a complete message before passing it on. Have a look at the examples in Serial Input Basics