Spectrum Satellite API for Arduino

I was working on a small project to implement the Spectrum Satellite Receiver Protocol on an Arduino. The project should work with any type of board (e.g. Arduinos, ESP32, ESP8266 etc)

• Complete Implementation of the Spektrum Satellite Specification
• Support for sending data e.g. to build a Remote Control Transmitter
• Support for receiving data e.g. to build a Remote Control Receiver
• Support of different data types and automatic scaling of channel values
• Support of logging using a specified Serial pin
• Provides Serialization to and from CSV format

Basic Syntax

The SpektrumSatellite class expects a Stream (HardwareSerial, SoftwareSerial, UDP etc) as parameter. You need to make sure that you set the exected baud rate (e.g. with Serial.begin(SPEKTRUM_SATELLITE_BPS) if this is necessary. The most important methods are:

• setChannelValue(channel, value)
• sendData()
• getFrame()
• getChannelValue(channel)

If you want to work with 16bit unsigned integer numbers you define SpektrumSatellite<uint16_t> and if you want to use floats instead you can define SpektrumSatellite<float>.

You can also work with your own value range by calling setChannelValueRange(fromValue, toValue);

Example: Implementing a Remote Control

In this Example we use of the SpektrumSatellite class to read the data from analog lines and send it via UDP: With this we can implement a simple custom remote control running on a ESP32 which reads the joystick values and sends them out to a receiver.
Please check and adapt the pin assignments of your Microcontroller.

#include "SpektrumSatellite.h"
#include "SpektrumCSV.h"

#ifdef ESP32
  #include <WiFi.h>
  #include <WiFiClient.h>
  #include <WiFiUdp.h>
#else
    #error "This demo requires an ESP32 or ESP8266 -> Please convert the sketch to your board"
#endif


char* ssid = "RemoteControl";                
char* password =  "password123";   

IPAddress local_IP(192,168,4,1);
IPAddress gateway(192,168,4,0);
IPAddress subnet(255,255,255,0);   
IPAddress target_IP(192,168,4,2);

const int udpPort = 6789;
unsigned long intervall = 500;  // send every 500ms (=2 messages per second)
unsigned long intervallTime;
WiFiUDP udp;

SpektrumSatellite<uint16_t> satellite(udp); // Assigning the Sattelite to use UDP
SpektrumCSV<uint16_t> csv;

const int pins = 6;  // number of channels for servos
int inPins[] = {16, 5, 4, 0, 10, 9};  // analog input pins 
uint8_t buffer[1024];

void setup() {
  Serial.begin(115200);
  Serial.println();
  Serial.println("setup");

  //Initiate connection
  WiFi.disconnect(true);

  WiFi.softAPConfig (local_IP,gateway,subnet);
  WiFi.softAP(ssid, password);
  IPAddress myIP = WiFi.softAPIP();
  Serial.print("AP IP address: ");
  Serial.println(myIP);
  Serial.println("Access Point started");

  // Activate the logging to the console only if SpektrumSatellite is not using Serial
  satellite.setLog(Serial);
  satellite.setLogMod(0); // do not log records

  // setup Input pins
  for (int j=0;j<pins; j++){
    pinMode(inPins[j],INPUT);
  }
}

void loop() {

  if (millis()>intervallTime) {
    intervallTime = millis()+intervall;

    // read values from pins
    for (int j=0;j<pins; j++){
      int value = analogRead(inPins[j]);
      Channel channel = (Channel) (j+1);
      satellite.setChannelValue(channel, analogRead(inPins[j]));
    }

    // send binary data
    udp.beginPacket(target_IP, udpPort);
    satellite.sendData();
    udp.endPacket();

    // log data as CSV to console
    csv.toString(satellite, buffer, 1024);
    satellite.sendData(buffer);   
    Serial.print((char*)buffer);      

  } 
}

Example: Implementing the Receiver on the RC Airplane

In the following Example we use the SpektrumSatellite class on an ESP32 to receive the data in order to update the servos.

#include "SpektrumSatellite.h"
#include "SpektrumCSV.h"
#include "ESP32_Servo.h"

#ifdef ESP32
  #include <WiFi.h>
  #include <WiFiUdp.h>
#else
    #error "This demo requires an ESP32 or ESP8266 -> Please convert the sketch to your board"
#endif


char* ssid = "RemoteControl";                 //Change this to your router SSID.
char* password =  "password123";        //Change this to your router password.
const int udpPort = 6789;
IPAddress gateway(192,168,4,0);
IPAddress subnet(255,255,255,0);   
IPAddress local_IP(192,168,4,2); 
WiFiUDP udp;

SpektrumSatellite<uint16_t> satellite(udp); // Assing satellite to Serial (use Serial1 or Serial2 if available!)
SpektrumCSV<uint16_t> csv;

const int pins = 6;  // number of channels for servos
int pwmPins[] = {2, 0, 4, 5, 6, 7};  // servo pins 
Servo servos[pins];  // allocate servos for all channels
uint8_t buffer[1024];


void setup() {
  Serial.begin(115200);
  Serial.println();
  Serial.println("setup");

  //Initiate WIFI Hostspot connection
  WiFi.disconnect(true);
  WiFi.config(local_IP, gateway, subnet);
 // WiFi.mode(WIFI_STA);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print('.');
    delay(500);
  }
  Serial.println("Connected to WIFI");

  // Activate the logging to the console only if SpektrumSatellite is not using Serial
  satellite.setLog(Serial);
  satellite.setLogMod(0);

  // setup PWM pins
  for (int j=0;j<pins; j++){
    //servos[j].attach(pwmPins[j]);
  }

  // start to listen for data
  if (udp.begin(udpPort))
    Serial.print("Processing UPD now...");

}


void loop() {
  // Start processing the next available incoming packet
  if (udp.parsePacket()>0){
    if (satellite.getFrame()) {   
      for (int j=0;j<pins; j++){
         Channel ch = static_cast<Channel>(j);   
         long value = satellite.getChannelValue(ch);
         //servos[j].write(value);
      }  

      // log data as CSV to console
      csv.toString(satellite, buffer, 1024);
      satellite.sendData(buffer);   
      Serial.print((char*)buffer);       
    } 
  }

}

Installation

You can download this project as ZIP and in the Arduino IDE use -> Sketch -> Include Library -> Add ZIP Library.

The recommended way howerver is to clone the project to your libraries directory. E.g. with

    cd ~/Documents/Arduino/libraries
    git clone https://github.com/pschatzmann/SpektrumSatellite.git