CO2 sensor MHZ17 error ppm not declared in this scope

Projects Programming
1

I have a MHZ19 and I got it working only with the serial plotter and monitor.
I want to make leds blink. but dont know how.
At first I have the working version. then with an addition arduino says PPM is not declared.
I cant continu.
Who knows the anser.

Working:

#include <SoftwareSerial.h>;

SoftwareSerial mySerial(A0, A1); // connect also co2sensor-ardunoUno17 with Tx-A0,Rx-A1,Vin-5v,GND-GND ,Old bootloader in my case

byte cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79};
unsigned char response[9];

void setup() {
Serial.begin(9600);
mySerial.begin(9600);
}

void loop()
{
mySerial.write(cmd, 9);
memset(response, 0, 9);
mySerial.readBytes(response, 9);
int i;
byte crc = 0;
for (i = 1; i < 8; i++) crc+=response*;*

  • crc = 255 - crc;*
  • crc++;*
  • if ( !(response[0] == 0xFF && response[1] == 0x86 && response[8] == crc) ) {*
  • Serial.println("CRC error: " + String(crc) + " / "+ String(response[8]));*
  • } else {*
  • unsigned int responseHigh = (unsigned int) response[2];*
  • unsigned int responseLow = (unsigned int) response[3];*
    _ unsigned int ppm = (256*responseHigh) + responseLow;_
  • Serial.println(ppm);*
  • }*
  • delay(10000);*
    }
    Not working. ppm was not declared??
    #include <SoftwareSerial.h>;
    SoftwareSerial mySerial(A0, A1); // connect also co2sensor-ardunoUno17 with Tx-A0,Rx-A1,Vin-5v,GND-GND ,Old bootloader in my case
    byte cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79};
    unsigned char response[9];
    void setup() {
  • Serial.begin(9600);*
  • mySerial.begin(9600);*
    }
    void loop()
    {
  • mySerial.write(cmd, 9);*
  • memset(response, 0, 9);*
  • mySerial.readBytes(response, 9);*
  • int i;*
  • byte crc = 0;*
    _ for (i = 1; i < 8; i++) crc+=response*;_
    _     crc = 255 - crc;_
    _     crc++;_
    _     if ( !(response[0] == 0xFF && response[1] == 0x86 && response[8] == crc) ) {_
    _     Serial.println("CRC error: " + String(crc) + " / "+ String(response[8]));_
    _     } else {_
    _     unsigned int responseHigh = (unsigned int) response[2];_
    _     unsigned int responseLow = (unsigned int) response[3];_
    _ unsigned int ppm = (256responseHigh) + responseLow;_
    * Serial.println(ppm);*
    * }*
    * delay(10000);*
    * // nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn*
    * if(ppm == 0) {*
    * Serial.println("PANIC!!");*
    * }*
    * if(ppm < 500) {*
    * Serial.println("Oh oh,... we have less!!");*
    * }*
    * if(ppm > 500) {*
    * Serial.println("Woohoo - we are rich!!");*
    * }*
    //mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
    * Serial.println("-----------");*
    * delay(5000);*
    }
2

ppm is defined within the braces of the else statements, that limits it scope.

it can't be referenced outside the braces.

   } else {
        ...
        unsigned int ppm = (256*responseHigh) + responseLow;
        ...
    }

    ...

    if(ppm == 0) {
3

Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

How do you want to make the LEDs blink?

Tom... :slight_smile:

4

Report to moderator is not the correct way to add a post

instead of the words panic ,enoug CO2 Or Ahigh level off CO2 (ppm) I want to activate the digital out ports.
But when I write my code at once it wil have errors. I want to make small program steps.

5

maybe this ihas a better layout.

But how do I put my ppm variable in the declarations.

not working code (error ppm is not declared in this scope.

#include <SoftwareSerial.h>;

SoftwareSerial mySerial(A0, A1); // connect also co2sensor-ardunoUno17 with  Tx-A0,Rx-A1,Vin-5v,GND-GND  ,Old bootloader in my case

byte cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}; 
unsigned char response[9];

void setup() {
  Serial.begin(9600);
  mySerial.begin(9600);
}

void loop() 
{
  mySerial.write(cmd, 9);
  memset(response, 0, 9);
  mySerial.readBytes(response, 9);
  int i;
  byte crc = 0;
  for (i = 1; i < 8; i++) crc+=response[i];
  crc = 255 - crc;
  crc++;

   if ( !(response[0] == 0xFF && response[1] == 0x86 && response[8] == crc) ) {
    Serial.println("CRC error: " + String(crc) + " / "+ String(response[8]));
  } else {
    unsigned int responseHigh = (unsigned int) response[2];
    unsigned int responseLow = (unsigned int) response[3];
    unsigned int ppm = (256*responseHigh) + responseLow;
    Serial.println(ppm);
  }
  delay(10000);
  // nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
   if(ppm == 0) {
    Serial.println("PANIEK!!");
  }

  if(ppm < 500) {
    Serial.println("Oh oh,... we hebben maar weinig geld!!");
  }

  if(ppm > 500) {
    Serial.println("Woohoo - we zijn rijk!!");
  }


//mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
    Serial.println("-----------");
    delay(5000);
}

working code..

#include <SoftwareSerial.h>;

SoftwareSerial mySerial(A0, A1); // connect also co2sensor-ardunoUno17 with  Tx-A0,Rx-A1,Vin-5v,GND-GND  ,Old bootloader in my case

byte cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79}; 
unsigned char response[9];

void setup() {
  Serial.begin(9600);
  mySerial.begin(9600);
}

void loop() 
{
  mySerial.write(cmd, 9);
  memset(response, 0, 9);
  mySerial.readBytes(response, 9);
  int i;
  byte crc = 0;
  for (i = 1; i < 8; i++) crc+=response[i];
  crc = 255 - crc;
  crc++;

   if ( !(response[0] == 0xFF && response[1] == 0x86 && response[8] == crc) ) {
    Serial.println("CRC error: " + String(crc) + " / "+ String(response[8]));
  } else {
    unsigned int responseHigh = (unsigned int) response[2];
    unsigned int responseLow = (unsigned int) response[3];
    unsigned int ppm = (256*responseHigh) + responseLow;
    Serial.println(ppm);
  }
  delay(10000);
}
6

in your working code, you're not trying to reference ppm outside the else braces.

define ppm -- unsigned int ppm; -- at the beginning of loop() after it's brace ({) and set the value of ppm with defining it as int within the else

void loop()
{
    unsigned int ppm;
    ...
    } else {
        ...
        ppm = (256*responseHigh) + responseLow;
        ...
    }

    ...
    if(ppm == 0) {
        Serial.println("PANIEK!!");
    }
    ...
7

I am going to try that. thanks already for the quick help.

8

Ok. :slight_smile: Only " unsigned int ppm; " in my scriot and the error was gone.
The topic can be closed. or how does it work.

9

We don't close the topic as it may be helpful to others but you might like to edit your original post and add [SOLVED] to the subject line