My android app is sending text but the arduino is receiving strange text like (oo), but when i write from the serial monitor it works perfectly

Projects Programming
1 
String Incoming_value = "";

int led =13;

void setup() {

Serial.begin(9600);

pinMode(led,OUTPUT);

}

void loop() {

 

  if(Serial.available()>0){

  Serial.println("enter on or off");

  Incoming_value=Serial.readString();

  Serial.println(Incoming_value);

  

  if(Incoming_value=="on"){

    digitalWrite(led,HIGH);

    delay(1000);}

   else if(Incoming_value=="off")

   digitalWrite(led,LOW); 

 

    }

}

Capture
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2

why are you printing a prompt -- "enter on or off" -- after received data is available? shouldn't the prompt be generated in setup() for the first time and after receiving subsequent messages?

why is there a 1 sec delay after turning on the led? the led is only being turned off after receiving an "off"

3

yes you are right but this is not the problem.
The problem is when i click on button 1 to send an (on) message, the serial monitor reads the on message in a strange way.

As you can see in the picture i provided, at first i send from the serial monitor and it worked perfectly but when i click on the android app to send a an on or off message, the serial monitor prints something strange like oo and oww.
2

4

i'm not that familiar with reading "Strings" using readString(). it's not obvious to me that the String is deallocated or overwritten when used this way

have you considered using readBytesUntil() and a char buffer, char buf [80];, which doesn't rely on a timeout

5

can you write for me the code using readbytesuntil() and what should i do in app inventor

6 
enum { Off = HIGH, On = LOW };
char buf [80];

// -----------------------------------------------------------------------------
void
loop (void)
{
    if (Serial.available ())  {
        int n = Serial.readBytesUntil ('\n', buf, sizeof(buf));
        buf [n] = '\0';

        if (! strcmp (buf, "on"))
            digitalWrite (LED_BUILTIN, On);
        else if (! strcmp (buf, "off"))
            digitalWrite (LED_BUILTIN, Off);
        else
            Serial.println (buf);
    }
}

// -----------------------------------------------------------------------------
void
setup (void)
{
    Serial.begin (9600);
    pinMode (LED_BUILTIN, OUTPUT);
    digitalWrite (LED_BUILTIN, Off);
}
7

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