Which pins to use for the serial communication for CNC pendant?

ryanaukes · May 6, 2025, 5:12pm

Hi everyone, I hope someone can help me out. I have made a CNC pendant based on this project, but I am not sure which pins I should connect it to. I am using a BTT SKR PRO 1.2 mainboard with a BTT TFT35 touch screen. Which pin (tx and rx) can I connect the CNC pendant to?

MakerJim · May 6, 2025, 9:59pm

From the project you linked (comments)

NapierDeltic

August 29, 2023

Hi Armin. I’m pretty sure that the code is very correct but please confirm:
D1 and D2 from ESP8266 should be connected to both Display’s and PCF8574’s SDA and SCL; they should be connected in parallel on the same 2 pins.
I am at perfboard’s connections “design” -spider wires traces. I want to avoid magic smoke or other issues (failure -moral- most).
Thank you very much for your version of this pendant! I build both v2 and v3 versions in parallel.
Second question; talking with Josh/Ornerymaker I figured I have bought slightly different OLED than intended: SSD1315 instead SSD1306 (very close match). Can you help with custom code? It uses U8g2 lib (could be more as I found also one Adafruit_U8g2 lib). It seems U8g2 lib is a bit larger as it is a multi-LCD library. Actually, on current display with original display library the image is stretched vertically so I can see only the upper half (on v2). As I do not have full function on v2 I cannot make any other estimates.
Additional question (from a newbie): Your code mentions wi-fi lib and wi-fi commands. can the pendant communicate through wi-fi or it is an intended expansion or something else?
Thank you,
Mihai

Arminth

August 29, 2023

Hi Mihai,
You are correct with d1 d2 wiring. It is a bus. The two devices are just connected in parallel.
WiFi is only used for OTA update functionality.
As I don’t have your specific display, it’s hard for me to provide verified code. Maybe, you do some experiments on the breadboard with the library.
Be also aware that with a bigger screen, the case might not fit!
Cheers
Armin

NapierDeltic

August 29, 2023

Hi Armin, thank you for your answer!
The display is physically the same -0.96 inch IIC 128x64 ; just different standard (or something else…). This is the reason I was “fouled” to order it -because not looking deeper at spec.
Like this; but not necessarily the same… Grove - OLED Display 0.96" (SSD1315) | Seeed Studio Wiki

ryanaukes · May 7, 2025, 6:00am

Hi! Thanks for your reply. I think my question was not stated clear enough. The pendant I made is done and working, but i don’t know how to connect the pendant to the SKR PRO 1.2. I know I should connect it to tx and rx pins of the SKR, but I am not sure which pins on the SKR PRO 1.2 are tx and rx pins which I can use.

Bartman · June 13, 2025, 3:54am

Not sure if the SKR pro v1.2 actually has Tx & Rx (serial) ports as such. Certainly no spares on the board labelled Tx and Rx.

There are serial ports, but they are used for the TFT/display. There is a USB (B) port that I think is effectively a serial connection.

If you plan on using the pendant in place of the display, you may be able to use one of the TFT or Display1/Display2 ports. You should be able to determine which pins are which by using Google to search for the board pinouts…

Alternatively you may be able to find a Serial-USB converter and wire into the DB9 pins from your pendant.

Best of luck