This library communicates with SBUS receivers and servos and is built for use with the Arduino IDE.

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SBUS is a bus protocol for receivers to send commands to servos. Unlike PWM, SBUS uses a bus architecture where a single serial line can be connected with up to 16 servos with each receiving a unique command.

The SBUS protocol uses an inverted serial logic with a baud rate of 100000, 8 data bits, even parity, and 2 stop bits. The SBUS packet is 25 bytes long consisting of:

• Byte[0]: SBUS header, 0x0F
• Byte[1 -22]: 16 servo channels, 11 bits each
• Byte[23]
  • Bit 5: frame lost (0x20)
  • Bit 4: failsafe activated (0x10)
• Byte[24]: SBUS footer

Note that lost frame is indicated when a frame is lost between the transmitter and receiver. Failsafe activation typically requires that several frames are lost in a row and indicates that the receiver has moved into failsafe mode. Packets are sent approximately every 10 ms. FrSky receivers will output a range of 172 - 1811 with channels set to a range of -100% to +100%. Using extended limits of -150% to +150% outputs a range of 0 to 2047, which is the maximum range acheivable with 11 bits of data.

Because SBUS is a digital bus format, it is an excellent means of receiving pilot commands from a transmitter and an SBUS capable receiver. If SBUS servos are used in the aircraft, SBUS is also an excellent means of sending actuator commands - servo commands can often be sent with lower latency and, by only using a single pin to command up to 16 servos, additional microcontroller pins are freed for other uses.

SBUS uses an inverted serial protocol, which is not commonly supported in Arduino. This library is able to use inverted serial for the following microcontrollers:

• Teensy 3.x
• Teensy 4.x
• Teensy LC
• STM32L496xx
• STM32L476xx
• STM32L433xx
• STM32L432xx

For all other microcontrollers, you must use a serial inverter.

Simply clone or download and extract the zipped library into your Arduino/libraries folder. The library is added as:

#include "sbus.h"

SbusRx(HardwareSerial *bus) Creates an SbusRx object. A pointer to the Serial object corresponding to the serial port used is passed. The RX pin of the serial port will receive SBUS packets.

SbusRx sbus(&Serial1);

void Begin() Initializes SBUS communication.

sbus.Begin();

bool Read() Parses SBUS packets, returns true on successfully receiving an SBUS packet.

if (sbus.Read()) {
   // Do something with the received data
}

std::array<uint16_t, 16> rx_channels() Returns the array of received channel data.

std::array<uint16_t, 16> sbus_data = sbus.rx_channels();

bool lost_frame() Returns true if a frame has been lost.

bool lost_frame = sbus.lost_frame();

bool failsafe() Returns true if the receiver has entered failsafe mode.

bool failsafe = sbus.failsafe();

SbusTx(HardwareSerial *bus) Creates an SbusTx object. A pointer to the Serial object corresponding to the serial port used is passed. The TX pin of the serial port will transmit SBUS packets.

SbusTx sbus(&Serial1);

void Begin() Initializes SBUS communication.

sbus.Begin();

void Write() Writes an SBUS packet. The packet is written immediately, you should regulate timing of sending packets to servos to maintain a frequency of approximately 100 Hz or 50 Hz, depending on the setup of the SBUS system.

sbus.Write();

void tx_channels(const std::array<uint16_t, 16> &val) Sets the channel data to be transmitted.

sbus.tx_channels(sbus_tx_data);

std::array<uint16_t, 16> tx_channels() Returns the array of channel data to be transmitted.

std::array<uint16_t, 16> sbus_tx_data = sbus.tx_channels();