# Free UARTs TX and RX pins on CR-10S motherboard

I have a WiFi module that only needs two wires connection to work. These are RX and TX pins connected to Arduino or the CR-10S printer board but I don't know if there is any physical or software UARTs TX and RX pins. My goal is to add a Wifi support to the CR-10S printer. Since this is not Arduino and the pins are not labeled, it's hard to tell which TX and RX pins are not being used.

In the image of my motherboard below, any port or pin with line pointing to is considered as being used by the printing software so I can't used them.

There are still ports or pins that are not used. Can any one tell if there is a TX and RX pin that is not being used from the image above? I need them to communicate with the printer wirelessly.

Not answering the question directly which pins you can use I would like to propose an alternative solution for your problem, to explain why you should not use RX/TX pins.

An alternative solution includes the use of a small single board computer like the Raspberry Pi (RPi) which is connected over USB with the printer board. E.g. the latest range of RPi (Raspberry Pi 3 Model B and B+) have onboard WiFi, or alternatively an older RPi (Raspberry Pi 2) could be used in conjunction with a USB Wifi dongle. On the RPi you could install a print server that talks directly with your printer over USB. One such an application that is frequently used is OctoPprint (the complete installation/image is referred to as OctoPi).

You can then interface with the print server application using a web browser on any mobile device in your network, and if configured as such you could do that potentially from over everywhere over the world. The major advantage is that you then are not communicating G-code over WiFi as you would if you used RX/TX pins. Knowing that WiFi connection adds issues with latency and the possibility of a disconnection during the print, your fail rate would increase over a single board computer approach.

With an RPi the print will continue regardless of the Wifi connection.

• I know I can use Raspberry Pi but trying to avoid that. I just want to make a mod with my cheap \$5 wifi module on top my current and original motherboard. Nov 22, 2018 at 15:58

You see those 8 holes on the top left of the board? The bottom right one is RX, the one right above it is TX. These 8 pins are collectively known as "AUX1".

Here is the complete pinout (in the same orientation as the image above).

 5V • • 5V
GND • • GND
A3 • • TX0
A4 • • RX0