I cant get the bool function work properly

Projects General Guidance
1

hey guys, let me briefly explain what i am trying to do:

i have a raspberry pi (rpi from now on) and an arduino uno (uno from now on).

i have connected a pair of nrf24l01 to both my rpi and uno. the idea is, uno will read temp and send it to rpi. but i dont want uno to constantly read and send the data; i want uno to read the temp whenever i want it to read. for this purpose i switch uno to listener and rpi to writer.

what i am trying to do is: i am sending an "onn" message from rpi, and arduino will receive the message. if it confirms that it is an "onn" message, then uno will switch back to writer and read the temp and send it to rpi.

so guys, if i was clear with my explanation, this is the part of my code in uno that listens from rpi:

void fromPi() {
  const uint64_t listen_addr = 0xF0F0F0F0E0LL;
  radio.openReadingPipe(1,listen_addr);
  radio.enableDynamicPayloads();
  radio.powerUp();
  radio.startListening();
  char msg[] = {0};

  if(radio.available()) {
    radio.read(msg,radio.getDynamicPayloadSize());
    //Serial.println(msg);
    String decoded(msg);

    if (decoded == "onn") {
      Serial.println("inside on");
      decoded == "something else";
      
    } 
    else if (decoded != "onn") {
      Serial.println("inside else");
    }
  }
}

this piece of code works, when i send "onn" from rpi, it will print "inside on". then if i stop sending "onn" from rpi, arduino wont print out anything.
upon seeing this result, i changed the code to look like this:

bool fromPi() {
  const uint64_t listen_addr = 0xF0F0F0F0E0LL;
  radio.openReadingPipe(1,listen_addr);
  radio.enableDynamicPayloads();
  radio.powerUp();
  radio.startListening();
  char msg[] = {0};

  if(radio.available()) {
    radio.read(msg,radio.getDynamicPayloadSize());
    //Serial.println(msg);
    String decoded(msg);

    return decoded == "onn";
  }
}

since this is a bool function, i wanted it to return either 0 or 1, just like how serial.available returns 0 or 1. but for some reason it returns 55. also, if i start my rpi code, meaning if i send "onn" message, then it returns 1. but if i stop my rpi code, meaning i wont send "onn" message, it still returns 1.

i want my code to work just like serial.available. what to and what not to do?

thanks in advance

2

What if there is no message from the radio?
What does your function return?

3

Actually, Serial.available() returns the number of bytes available to read

char msg[] = {0};

An array with one element ?
How many characters do you expect it to hold ?

Why all the messing around with Strings ? Read the message into the correctly sized msg array, compare it with "onn" and return true or false depending on the outcome of the comparison but always return one or the other

4

yes but, if i dont send anything from rpi, then shouldnt it just return 0?

5

If you don't explicitly return anything then I don't know what it will return. Why not do it properly and return true or false explicitly ? Of course, you don't even call the function unless you have actually received something from the Pi

6

i actually tried to do what you said, but i couldnt compare an array with a string. and making msg[0] == "o" and such didnt work either. i dont know how these things work actually

7

i thought making

if (decoded == "onn") { return true;}

and

return decoded == "onn";

were the same?

8

strcmp

1 Like
9

I am guessing but it looks like

radio.read(msg,radio.getDynamicPayloadSize());

puts the message in the msg array which must be declared large enough to hold it. Once received, if it is correctly terminated with a '\0' to turn it into a C style string (lowercase s) then you can use the strcmp() function to compare it with "onn"

What sort of wireless communication system are you using ? RF24 perhaps ?

1 Like
11

nrf24l01

i will try what you said, thank you

12

Are you sending the terminating '\0' from the Pi ?

13

no i dont. but i think the library handles that itself. because i can correctly send and receive all the messages i want. i just cant make it return 0 or 1 depending on the message i sent

14

No, not at all.

15

huh

16

What does the first one return, if the Strings are not the same?

17

right now, if the strings are not the same it returns 0, hen if the strings are the same it returns 1. and this is what i wanted. but then, after it returned 1, it always returns 1. that is the problem

18

How do you know that?
The first snippet has no return if the Strings don't match.

19

i thought you meant the thing i originally posted

20

Please post an example of receiving and printing a message

21

i will when i run the system again. i am going home now