Can't get original value after sending by serial port - c++

Question

I have written a simple code for sending int value using bluetooth serial port.
Transmitter:
#include <SoftwareSerial.h>
#include "PWM.hpp"
PWM PWM(2);
SoftwareSerial BTSerial(8,9);
void setup()
{
Serial.begin(9600);
Serial.println("Go");
BTSerial.begin(9600);
BTSerial.write("AT+INQ\r\n");
delay(10000);
BTSerial.write("AT+CONN1\r\n");
delay(100);
PWM.begin(true);
}
void loop()
{
int pwmValue = PWM.getValue();
Serial.println(pwmValue);
BTSerial.write(pwmValue);
delay(100);
}
Output of Serial.println of transmitter part is correct:
1500
but on receiver part isn't. This is the code of receiver:
#include <SoftwareSerial.h>
SoftwareSerial BTSerial(8, 9);
void setup() {
Serial.begin(9600);
BTSerial.begin(9600);
BTSerial.write("AT+NAME=Remote\r\n");
}
void loop() {
if (BTSerial.available()) {
int pwmValue = BTSerial.read();
Serial.println(pwmValue);
}
Incorrect output of Serial.println is:
220
I think the issue is in typecasting.

Answer 1

SoftwareSerial::read is returning a single byte read.
If you examine the expected 1500 in hexadecimal it is 0x05DC, and it's lower byte is 0xDC which is exactly 220 in decimal.

Answer 2

With the multi-byte variant of write() you could use:
BTSerial.write(&pwmValue, sizeof pwmValue);
For receiving you need a loop:
union {
int i;
char c[0];
} pwmValue;
int receivedBytes = 0;
void loop() {
if (BTSerial.available()) {
pwmValue.c[receivedBytes] = BTSerial.read();
receivedBytes++;
if (receivedBytes == sizeof pwmValue) {
Serial.println(pwmValue.i);
receivedBytes = 0;
}
}
}

Answer 3

In documentation https://github.com/PaulStoffregen/SoftwareSerial/blob/master/SoftwareSerial.cpp, you can see that both functions work with uint_8t -- which is guaranteed to have 8 bits (1 byte). That holds up to 256 of value, so 1500 mod 256 is 220.
Looks like the library is prepared to transmit only char-sized data, so you need to convert bigger numbers on both size.
For sending int:
int n = pwmValue;
while (n > 0) {
int digit = n % 10;
n = n / 10;
BTSerial.write(digit);
}
For receiving int:
int n = 0; //future result
int decs = 1;
int temp;
while ((temp = BTSerial.read()) != -1) {
n += temp * decs;
decs *= 10;
}