Arduino String Comparison

Question

I have some data coming in through bluetooth serial and I have a very simple if statement to decide what to do next, however it is not firing as expected. I am total Arduino newb, does anyone know why this is happening?

Here is the log output as well as the full code, the main suspect at the moment is controlArm method.

Log Output

01:41:37.678 -> A
01:41:37.678 -> 
01:41:37.678 -> 
01:41:37.678 -> 
01:41:37.678 -> Received: A
01:41:37.678 -> controlArm (A)
01:41:37.678 -> Else Move
01:41:37.678 -> moveArm 0 90 45 180 180 90 10
01:41:43.286 -> 1
01:41:43.286 -> 
01:41:43.286 -> 
01:41:43.286 -> 
01:41:43.286 -> Received: 1
01:41:43.286 -> controlArm (1)
01:41:43.286 -> Else Move
01:41:43.286 -> moveArm 0 90 45 180 180 90 10
01:41:47.300 -> 2
01:41:47.300 -> 
01:41:47.300 -> 
01:41:47.300 -> 
01:41:47.300 -> Received: 2
01:41:47.300 -> controlArm (2)
01:41:47.300 -> Else Move
01:41:47.332 -> moveArm 0 90 45 180 180 90 10

Full Code:

#include <SoftwareSerial.h>
#include <Braccio.h>
#include <Servo.h>


Servo base;
Servo shoulder;
Servo elbow;
Servo wrist_rot;
Servo wrist_ver;
Servo gripper;

SoftwareSerial Bluetooth(8, 7);
int M0 = 0;
int M1 = 90;
int M2 = 45;
int M3 = 180;
int M4 = 180;
int M5 = 90;
int M6 = 10;

void setup() {  
    Bluetooth.begin(38400);   
  Serial.begin(9600);
  Braccio.begin();
  Braccio.ServoMovement(20,  20, 90, 90, 90, 90,  10); 

}

void moveArm(){
 
  Serial.println("moveArm " + String(M0) + " " + String(M1) + " " + String(M2) + " " + String(M3) + " " + String(M4) + " " + String(M5) + " " + String(M6));
  Braccio.ServoMovement(M0, M1, M2, M3, M4, M5, M6); 
  }



// This is the main suspect
void controlArm(String command){
  Serial.println("controlArm (" + command+")");
  if (command.equals("1")) {
    M6 = 0;
    moveArm();
  } else if (command == '2'){
    M6 = 30;
    moveArm();
  } else if (command == "A"){
    M6 = 73;
    moveArm();
  } else {
    Serial.println("Else Move");
    moveArm();
  }
}
  
  String Data = "";
void loop() {
  while(Bluetooth.available()){
    char character = Bluetooth.read();
    Serial.println(character);
    if (character == '\n'){
        Serial.print("Received: ");
        Serial.println(Data);
        controlArm(String(Data));
        Data = "";
    } else {
      Data.concat(character);
    }
  }

}

A String with "1\n" is not equals to "1". uses `command.charAt(0)=="1"`. — hcheung, Jul 11 '20 at 14:27
I suspect that there are 3 extra space characters in the string command, e.g. `"1 "` — tim, Jul 11 '20 at 15:46
@tim I thought that there may some characters around the value as well, so I added parans around it, didn't see anything. — nick_v1, Jul 11 '20 at 15:57
Looks like global M6 wasn't updated before the call of `moveArm()`. Try `volatile int M6 = 10;` — tim, Jul 11 '20 at 16:09

score 0 · Answer 1 · answered Jul 11 '20 at 07:09

0

So I am not sure what the issue was, but here is a better way of doing this that works, in the main loop:

void loop() {
  while(Bluetooth.available()){  
    String Data = Bluetooth.readStringUntil('\n');
    Serial.println(Data);
    controlArm(Data);
  }
}

answered Jul 11 '20 at 07:09

nick_v1

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I wouldn't call this a better way. If you don't have the '/n' at the end now then the program will stall for a second waiting for readStringUntil to time out. – Delta_G Jul 11 '20 at 13:51
What do you recommend? – nick_v1 Jul 11 '20 at 18:12
I wouldn't use the String class at all. It's a memory waste on small micros. I'd also just stick to reading one character at a time, keep things non-blocking. Serial data comes slowly. No reason to trap the code there waiting on the message to come in when you can read one character and get on with life while the next one comes down the wire. – Delta_G Jul 11 '20 at 18:15
Google "Arduino Robin2 Serial Input Basics" and spend a night reading. It's about reading from serial but the concept applies to any stream. – Delta_G Jul 11 '20 at 18:16

Arduino String Comparison

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