Serial.write causing void loop program to stop (Digital Pins stop responding) - arduino

Question

I have an issue trying to send some serial data through tx and rx to another arduino through a HC05 bluetooth module.
The overall project is developing a hybrid go kart and using the arduino as a simple ECU unit with a PID speed control over the PWM output controlling a DC motor. I have been working the project in steps and have go as far as setting up a footpedal with the arduino and controlling the electronic speed controller (ESC) directly. I have added a simple PID function to this along with a simple hall sensor to detect the speed and does require tuning but works great so far. Now the problem comes when I try to send data across over serial ports.
I have had the bluetooth modules connected with to separate arduinos and have successfully managed to send over data from one arduino with a pot input to another with a 3.5 inch TFT screen. When I try to integrate the master side of the project to the PID controlled DC motor the system freezes. I have since then removed the PID control and gone back to direct control and it still fails, i have tried commenting out the interrupt sequence for the encoder and put a static value for RPM and still freezes. the sending sequence works if I don't attempt to use any digital outputs. I am really confused. The code I have gone down to to try and debug this can be found below. This is not the full code and has been chopped to pieces to try and eliminate this fault. however in this code below, if I comment out the sendData function the system works and the motor spins with relative speed to the pedal input. as soon as I try to send the data the system runs for a seconds then freezes. the data is still being sent and the static readings are showing just the digital output seizes to work.
#include <TimerOne.h>
int previous = 0;
int Tavg = 0; // the average
int Tout = 0;
int throttle = A0;
const int numReadings = 10;
int readings[numReadings]; // the readings from the analog input
int readIndex = 0; // the index of the current reading
int total = 0; // the running total
int ESCPin = 5;
unsigned int counter=0;
int RPM;
long Time = 0;
long ReadInt = 0;
void docount() // counts from the speed sensor
{
counter++; // increase +1 the counter value
}
void timerIsr()
{
Timer1.detachInterrupt(); //stop the timer
Serial.print("Motor Speed: ");
RPM = (counter*75 ); // RPM= counterx10*60/8 (x10 for second, 8 counts in encoder, 60 minutes === 75x counter)
Serial.print(RPM);
Serial.println(" Rotation per min"); Serial.print(Tout);Serial.print("= "); Serial.print(Tout*0.01961);Serial.println("V");
counter=0; // reset counter to zero
Timer1.attachInterrupt( timerIsr ); //enable the timer
}
void ReadEnc (){
Timer1.initialize(100000); // set timer for 0.1sec
attachInterrupt(0, docount, RISING); // increase counter when speed sensor pin goes High
Timer1.attachInterrupt( timerIsr ); // enable the timer
}
void sendData(){
if (Serial.available()>0) {
if (Serial.read() == 0){
//Serial.println(sendChars);
int RPMout = RPM;
Serial.write("<");
//delay(2);
//Serial.write(sendChars);
Serial.write("Data is,");
//delay(2);
Serial.write( itoa (RPMout, 4,10));
//delay(2);
Serial.write(", 30, 48.35");
//delay(2);
Serial.write(">");
//delay(10);
Serial.println("");
}
}
}
void setup()
{
Serial.begin(9600);
pinMode(2, INPUT_PULLUP); // internal pullup input pin 2
pinMode(ESCPin, OUTPUT);
for (int thisReading = 0; thisReading < numReadings; thisReading++) {
readings[thisReading] = 0; }
Time = millis();
ReadInt = -100;
}
void ReadSensor (){
// get the sensor value
total = total - readings[readIndex];
// read from the sensor:
readings[readIndex] = analogRead(throttle);
//Serial.println(readings[readIndex]);
// add the reading to the total:
total = total + readings[readIndex];
// advance to the next position in the array:
readIndex = readIndex + 1;
// if we're at the end of the array...
if (readIndex >= numReadings) {
// ...wrap around to the beginning:
readIndex = 0;
}
// calculate the average:
Tavg = total / numReadings;
}
void loop(){
ReadSensor();
ReadEnc();
RPM = 1800;
Tout = map(Tavg, 180, 860, 0, 200);
if (Tout>0){
analogWrite(ESCPin, Tout);
}
if (Time > ReadInt + 5000) {
sendData (); // when this is commented it works fine, tried moving it everywhere
ReadInt = Time;
}
Time = millis();
}
If anyone has any ideas please let me know, and I know I probably haven't explained my problem well so if their is any questions or more details needed please ask.

Answer 1

Second parameter of itoa should be a pointer to output bufffer. but you do not need itoa. use Serial.print(RPM);. For string the print and write functions are the same, but for number print has a version for int