Requirements

Arduino IDE.
Arduino boards package for Arduino IDE.

Arduino Pro Mini 3.3V board.

RC receiver with up to 8 PWM output channels.

Wires: 24AWG...30AWG.

Compilation

Run Arduino IDE.
Open "pwm_to_sbus_pro_mini_3v3.ino".
Select board -> "Arduino Pro or Pro Mini".
Tools -> Processor -> "ATmega328P (3.3V, 8 MHz)".
Sketch -> Verify/Compile.
Sketch -> Upload.

Connection

Connect directly to the RCIN(SBUS) port of the controller.

TXD pin (arduino pin 1), white: 3.3V SBUS output
RAW pin, red: 5V power input
GND pin, black: GND

Arduino pins 2 to 9: PWM inputs.
CH1: pin 9
...
CH8: pin 2