I am not able to rerun the loop - arduino

Question

I am using HC-05 with arduino and controlling a motor.
I want a motor to run till a specific value (k) every time I send a character (Eg. 'R') from my app to Bluetooth. I am able to it once, but when I send 'R' again, It doesnot work.
I want that the motor should run whenever I send the character 'R'.
Arduino code
#define stpwm 13
#define stdir 12
int j=0;
int k=20;
char inChar;
void setup() {
Serial.begin(9600);
pinMode(stpwm, OUTPUT);
pinMode(stdir, OUTPUT);
}
void loop() {
if (Serial.available() > 0 ) { // Checks whether data is comming from the serial port
inChar = (Serial.read()); // Reads the data from the serial port
}
if (inChar == 'R')
{
if (j<=k)
{
analogWrite(AN2, 100);
analogWrite(AN1, 50);
analogWrite(stpwm, 50);
digitalWrite(stdir, HIGH);
digitalWrite(IN1, HIGH);
digitalWrite(IN2, LOW);
delay(100);
Serial.println(j);
j++;
}
analogWrite(stpwm,0);
}

Answer 1

Try
if (inChar == 'R')
{
while (j<=k)
{
analogWrite(AN2, 100);
analogWrite(AN1, 50);
analogWrite(stpwm, 50);
digitalWrite(stdir, HIGH);
digitalWrite(IN1, HIGH);
digitalWrite(IN2, LOW);
delay(100);
Serial.println(j);
j++;
}
j=0;
analogWrite(stpwm,0);
}

Answer 2

There is one main issue with your code:
the variable you use to control the if statement never resets, so it comes a time (when j >= k) that it can never be true unless you restart the system;
Although Pradeep's answer has potential to work, it would lock your system in a loop, while j is less then k.
Therefore, if you want to implement future control code in your system, this could become an issue. For instance, if you need to have an emergency stop set as another letter, this would only be read if you're not stuck within the while loop.
I'd recommend making use of a very simple structure: else; as per below:
#define stpwm 13
#define stdir 12
#define k 20
uint8_t j=0;
char inChar[1];
void setup() {
Serial.begin(9600);
pinMode(stpwm, OUTPUT);
pinMode(stdir, OUTPUT);
}
void loop() {
if (Serial.available() > 0 ) { // Checks whether data is comming from the serial port
inChar = (Serial.read()); // Reads the data from the serial port
}
if (inChar == 'R')
{
if (j<=k)
{
analogWrite(AN2, 100);
analogWrite(AN1, 50);
analogWrite(stpwm, 50);
digitalWrite(stdir, HIGH);
digitalWrite(IN1, HIGH);
digitalWrite(IN2, LOW);
delay(100);
Serial.println(j);
j++;
}
}
else{
// resets both j and inChar, so that the iteration does not restart
j = 0;
inChar = "";
// turn off signal only when this criteria is met: j > k
analogWrite(stpwm, 0);
}
}
I also made some minor changes to your code:
Defined k as a constant, as you won't be changing it on your program
declared j as an 8-bit integer, which holds values that range from 0 to 255; this saves memory
modified the position where you were turning off stpwm. The way it was set, your signal always turned off at the end of each iteration, which could damage your motor (you were, in a way implementing another pulse modulation)
Hope this helps.