Board definitions are available for both the Atmega328p and STM32F103C boards. The board definitions make it easier to compile and install the multiprotocol module firmware.

Installing

The board definitions are installed using the Arduino IDE Boards Manager.

Open the Arduino IDE
Go to File -> Preferences, or press Ctrl+Comma
Locate the Aditional Boards Manager URLs field and paste in this URL: https://raw.githubusercontent.com/pascallanger/DIY-Multiprotocol-TX-Module/master/BootLoaders/package_multi_4in1_board_index.json

Note: Multiple URLs are comma-separated.

Click OK to save the change
Click Tools -> Board -> Boards Manager
Type multi into the search box to see the Multi 4-in-1 boards

Click on the board you require and click the Install button. Repeat for both boards, if required. If you are installing the STM32 board for the first time, and you have not installed any STM32 or SAMD boards before (such as Arduino Due or Zero) the dependency toolchain will also be downloaded and installed.
Click Close to close the Boards Manager

Verify the boards are installed

Click Tools -> Board
Scroll down the list to the Multi 4-in-1 board headings verify that the boards you installed are available:

Multi 4-in-1 (Atmega328p, 3.3V, 16MHz) for the Atmega board
Multi 4-in-1 (STM32F103CB) for the STM32 board

Compiling and Uploading

Refer to the hardware-specific pages for information on compiling the firmware and uploading it to the multiprotocol module: