Use of RX and TX GPIO on ESP32 Sparkfun Thing

Hello,

I am building a system that automates the measurement of soil hydraulic conductivity based around the ESP32 Thing, HX711 Load Cell Amplifiers and 10 kg load cells. The system also has an SD card attached.

I have built an initial prototype with three load cells connected which works with no problems.

I am now building a scale prototype with the aim of connecting 10 HX711/load cells. I currently have eight connected. 7 of the 8 HX711/load cells are working fine. One of them is not working however.

The one that is not working is connected to the RX and TX pins . I have declared these pins as follows based on the GPIO numbers detailed in the ESP32 Thing PINOUT guide.:

const int LOADCELLH_DOUT_PIN = 3; // RX(3) - Loadcell H 
const int LOADCELLH_SCK_PIN = 1; // TX(1)

LOADCELLH_DOUT_PIN connects to the data pin on the HX711

LOADCELLH_SCK_PIN connects to the clock pin on the HX711

However unlike the remainder of the HX711/load sensors, this one is not being recognised.

My question is can the RX and TX pins be used as GPIO pins? And if they can, have I declared these pins correctly?

Thankyou

The GPIO1 and GPIO3 (U0_TXD and U0_RXD) are connected to the USB for the board. Anything you connect here will interfere with any USB communication between the ESP32 and a PC