Transmitting data from GPS to SIGFOX - c++

Question

I'm working on an Arduino board (microprocessor: ATMega328P) for a University project. I'd like to build a GPS tracker which receives data, stores it, and retransmit it via SIGFOX module.
Basically, I'm able to receive data, and I'm able to send simple SIGFOX commands via serial.
#include <TinyGPS++.h>
#include <String.h>
#include <SoftwareSerial.h>
static const int RXPin = 4, TXPin = 3;
static const uint32_t GPSBaud = 4800;
TinyGPSPlus gps;
SoftwareSerial ss(RXPin, TXPin);
void setup()
{
Serial.begin(115200);
ss.begin(GPSBaud);
Serial.println(F("DeviceExample.ino"));
Serial.println(TinyGPSPlus::libraryVersion());
Serial.println();
}
void loop()
{
// This sketch displays information every time a new sentence is correctly encoded.
while (ss.available() > 0)
if (gps.encode(ss.read())) {
Serial.print(gps.location.lat(), 6); // 4 bytes
Serial.print(F(",")); // 1 byte
Serial.print(gps.location.lng(), 6); // 4 bytes
Serial.print('\n');
delay(4000);
}
if (millis() > 5000 && gps.charsProcessed() < 10){
Serial.println(F("No GPS detected: check wiring."));
while (true);
}
}
This prints correctly on screen the two values (latitude and longitude) that I need to store.
This is the part of the code in TinyGPS++.cpp :
double TinyGPSLocation::lat()
{
updated = false;
double ret = rawLatData.deg + rawLatData.billionths / 1000000000.0;
return rawLatData.negative ? -ret : ret;
}
double TinyGPSLocation::lng()
{
updated = false;
double ret = rawLngData.deg + rawLngData.billionths / 1000000000.0;
return rawLngData.negative ? -ret : ret;
}
Now I'd like to store this data and send it through the SIGFOX module.
A SIGFOX command is:
'N X'
Where N represents the number of bytes that are to be transmitted, and X are the values of the bytes. For example: '1 255' is 1 byte with value 255, and returns FF as output.
The problem is that the values are doubles so I don't know how to write them in the SIGFOX command.
Another problem is that I don't know how to create two serial communications in the code. I tried it but it doesn't seem to work.
Thank you so much in advance.

Answer 1

I saw some of the API info on the SIGFOX, I'm assuming it is this. Even if it isn't it's probably close enough for the point I'm trying to make.
https://support.sigfox.com/apidocs#operation/getDevice
You need to understand to some extent what IEEE 754 is as in my experience this is how equipment passes the data back and forth if you look at the raw bit stream.
https://en.wikipedia.org/wiki/IEEE_754
So, it is a double you send over 8 bytes on most platforms and 4 bytes for a float. When you print to the screen of hover over a variable in debug mode, the IDE/compiler takes care of this for you and gives you number with decimal points.
For making another serial port, you need to make another variable and pass in the baud rate etc of that device.