serialbridge_riff.ino

#include <SoftModem.h>

SoftModem modem = SoftModem();

void setup() {
	Serial.begin(9600);
	Serial.println("Booting");
	delay(100);
	modem.begin();
}

  int a;

void loop() {

 a = analogRead(A0);
String str=String(a);

int str_len = str.length() + 1; 

// Prepare the character array (the buffer) 
char char_array[str_len];

// Copy it over 
str.toCharArray(char_array, str_len);

Serial.println(char_array);

modem.write(char_array, str_len);

//a=a+1; // wraps at 32000

 delay(100); // 50 is too fast
 
}

https://www.daniweb.com/programming/software-development/threads/433247/sending-long-int-over-serial-byte-array-conversion