Arduino losing connection to Serial port after running function

Question

For some reason when I loop my code through a separate function the serial port hangs up. The serial connection appears fine when I call cases within the loop but not when I call outside.

I tried to figure out where the problem is and for some reason using the Serial.print(ComControlValue); and the output is

-1

But the error still persists.

Previous it was this before I changed the baudrate

-b⸮⸮⸮⸮ Waiting for Command

It's not printing out the -1 I'm using as the main case. Could this be the problem?

#include <Wire.h>
/* RPi Army variables */
int RPi[3] = {3,6,9}; // SDA/SCL code names for the different Raspberry pi's
/* Define parameters for computer control */
int ComControlValue = -1;
void setup() {
 Serial.begin(115200); // Establish Serial connection to computer
 Wire.begin(); // join i2c bus as master
}
void loop() {
 switch(ComControlValue){
 /* -1 : nothing happened yet */
 case -1:
 Serial.println("Waiting for Command");
 while (Serial.available()==0){}
 ComControlValue=Serial.parseInt(); // Pull value from serial port
 break; 
 case 111:
 Serial.println("Eat more Toast");
 ComControlValue = -1;
 break;
 case 210:
 Sendsignals(RPi[0],333);
 Sendsignals(RPi[1],333);
 Sendsignals(RPi[2],333);
 ComControlValue= -1;
 Serial.print(ComControlValue);
 break;
 }
} 
void Sendsignals(int Rpi, int code){
 char str[4];
 sprintf(str, "%3d\n", code);
 Wire.beginTransmission(Rpi); // transmit to device of choice
 Wire.write(str); // sends 16 bytes
 Wire.endTransmission(); // stop transmitting
}

• towe: Consider adding more debug lines during your Sendsignals function. Perhaps it hangs up during the Wire transmission. You should also consider changing sprintf to snprintf - apparently it's more robust against buffer issues, and requires the buffer size to be set manually.
• Hojo.Timberwolf: I tried that and it seems everything runs fine up until the break; when going through my separate function.
• Hojo.Timberwolf: Arduino Uno with an Adafruit motor shield
• Juraj: reconnecting Serial Monitor resets the board. while (Serial.available()==0){} blocks the loop
• Hojo.Timberwolf: Everything seems to work fine though when not calling Wire.h . Once I call the Wire.h functions the serial connection messes up.

Answer 1

Your str variable in function Sendsignals is short. sprintf writes 5 bytes to it, 3 digits, the \n and terminating zero. The terminating zero is written outside of the allocated array and causes the crash.

• Hojo.Timberwolf: This causes the serial terminal to disconnect? How to fix? Should I increase the str to 8 bits?
• Hojo.Timberwolf: Thanks. I changed the size of the str to 16 and it fixed the issue.
• Juraj: str[5] would be enough, if your codes have always 3 digits