How to connect to a GTR via an ESP32 WiFi Adapter


The GTR is an STM32F407ZGT6 based board.

Firmware File

Choose the correct corresponding firmware (firmware-stm32f4-wifi-XXX.bin) from here. Remember to rename it to firmware.bin. Put it in the root of a FAT32 formatted SD card. The maximum size supported card is 32GB.

TeamGloomy/Mellow Adapters

TeamGloomy and Mellow have teamed up to produce ESP32 adapters.
They can be purchased through aliexpress.

Connect the ESP32 Adapter to the board as shown below.

GTR ESP32 Adapter Connection

If not connecting the 4-pin serial cable, then add a small amount of solder in the area highlighted below.

Fly ESP32 Power
Fly ESP32 Power Solder

Homemade ESP32

Use an ESP32 with USB programming as it already 5v tolerant and it allows for updating via USB. They also need to be the 36 pin variety so they have GPIO0 broken out.


  • 1 x 36 pin ESP32
  • 1 x 330R resistor
  • jumpers or other ways of connecting to the GTR

Preparing the ESP32

Follow the instructions here.

Connecting the ESP32

The pinout for the GTR can be found here and the schematic for the Duet 2 WiFi for reference can be found here.

The table below shows the pins required on the ESP32 and what they are connected to on the GTR. Please ensure that your cables are no longer than 30cm although they should ideally be as short as possible.

ESP32 Pin GTR Pin Resistor Value
RST B.10 on EXP2 330R
VSPI SS/GPIO5 B.12 on EXP2 None
VSPI MOSI/GPIO23 B.15 on EXP2 None
VSPI MISO/GPIO19 B.14 on EXP2 None
VSPI SCK/GPIO18 B.13 on EXP2 None
ESP_DATA_Ready/GPIO0 D.10 on EXP2 None
LPC_DATA_Ready/GPIO4 H.10 on EXP2 None
VIN(5v) 5v on EXP2 None
GND GND on EXP2 None
ESP32 Pinout
ESP32 Pinout

Prepare the SD Card

Follow the instructions on Getting Started with RRF3

Board.txt file

You will also need a board.txt file in the sys folder. Below are the contents that should be used.

//Config for GTR
board = biqugtr_1.0
8266wifi.espDataReadyPin = D.10
8266wifi.TfrReadyPin = H.10
8266wifi.espResetPin = B.10
heat.tempSensePins = { C.0, C.1, C.2, C.3, A.3, F.9, F.10, F.7, F.5 }

Updating the ESP32 by RRF

If you have a WiFi adapter that supports updating via RRF, you need to add the following information to the board.txt file.

8266wifi.serialRxTxPins = { C.7, C.6 }
serial.aux.rxTxPins = { D.9, D.8 }

Smart Drivers

If using TMC5160 or TMC22XX drivers (where 22XX is either the TMC2208, TMC2209, TMC2225 or TMC2226), the following line must also be added to the board.txt file

stepper.numSmartDrivers = X

Where X is the number of drivers fitted in total.

TMC22XX UART Drivers

The drivers must be continuous and start at unit 0 (unless TMC5160 are also used, which case they must be installed after them). So, for the SKR board, if you have say 3 TMC2208s and 1 other driver, the 2208s must be in slots 0, 1, 2 and the remaining driver in slot 3 or 4. You can use RRF to assign any of those slots to an axis/extruder.

TMC5160 SPI Drivers

TMC5160 drivers are supported from 3.3 beta 1 onwards. If using TMC5160 drivers, the following lines must also be added to the board.txt file.

stepper.num5160Drivers = X
stepper.spiChannel = 5
SPI5.pins={ B.3, B.6, G.15 }

Where X is the number of 5160 drivers fitted. The drivers must be continuous and start at unit 0. So, if you have say 3 TMC5160s and 1 TMC22XX and 1 other driver, the 5160s must be in slots 0, 1, and 2, the TMC22XX in slot 3 and the remaining driver in 4. You can use RRF to assign any of those slots to an axis/extruder.

Sensorless Homing

Supported by only the TMC2209, TMC2226 and TMC5160 If using sensorless homing/stall detection with TMC2209 or TMC2226 the following line must be added to the board.txt file. It is not needed with TMC5160.

stepper.TmcDiagPins = { F.2, C.13, E.0, G.14, G.9, D.3, I.4, F.4, F.6, I.7, F.12 }

Please only include the diag pin numbers where you intend to use sensorless homing on that axis.
For example, if you only intend to use sensorless homing/stall detection on driver 0 and driver 1, only include F.2 and C.13 in your board.txt file.
For more information about setting up sensorless homing, please read this.

Driver Diag Pin

Board.txt Location

Place the board.txt file in a directory called “sys” on the SD card and install the SD card in the GTR.

Final Setup

Once connected, power up the board using 12-24v and connect to the USB port on the board. Using a program such as putty. Follow the instructions here to set it up for RRF. Then type in the following

If updating the ESP32 using RRF, type the following.
M997 S1
Wait for the uploading of the WiFi firmware to finish. Then send the following
M552 S-1
Continue with the instructions below.
M552 S0
M587 S"your SSID" P"your password"
M552 S1

The blue light on the WiFi chip shoould then flash blue and will go solid when a connection has been established. The ip address will be shown on the serial connection. It is also possible to type just M552 to get the current ip address reported back.

The final thing to do is add the line “M552 S1” to your config file. This can be done through the web interface. This just ensures that the WiFi connection is started at start up. There is no need to add the M587 command as this is written permanently to the flash of the ESP32 chip.

Once up and running

You will need to PID tune your tools and your bed. Please be aware that bed tuning may take up to an hour and tool tuning normally takes around 15 minutes. If it takes longer, that is also fine as up to 30 cycles may be ran.

To tune the bed, run the following command, changing the temperature (the S value) if a different tuning temperature is required.

M303 H0 S60

To tune each tool, run the following command, changing the temperature (the S value) if a different tuning temperature is required. This proceedure will activate the part cooling fans during the final phase of the tuning process so their effect is taken into account. If your printer has more than one tool, make sure each one of them is tuned.

M303 T0 S220

Once the tuning is complete, either copy the M307 command into the heater definitions or send M500, ensuring you have M501 at the end of your config.g.
If the tuning fails at the end, carry on saving the values as in most cases the outputted values still work correctly.
If the values still result in a heater fault, please refer to this wiki page for information about how to adjust the values manually.