Problems when sending float (temperatur) with VirtualWire Arduino

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1 
// User Gareth    https://www.robotshop.com/letsmakerobots/user/2941
// Project Node   https://www.robotshop.com/letsmakerobots/node/12394

// Remote Receiving Temparature and Humidity over RF Link to LCD Display

// how to use VirtualWire to receive messages and display floating point values to SerialMonitor

// rx pin 23 on mega


#include 

#undef int

#undef abs

#undef double

#undef float

#undef round

void setup()

{

    Serial.begin(9600);	// Debugging only

    

        // Initialise the IO and ISR

    vw_set_ptt_inverted(true); // Required for DR3100

    vw_setup(2000);	 // Bits per sec

    vw_set_rx_pin(23);

    vw_rx_start();       // Start the receiver PLL running

}


void loop()

{

  

    uint8_t buf[VW_MAX_MESSAGE_LEN];

    uint8_t buflen = VW_MAX_MESSAGE_LEN;


    if (vw_get_message(buf, &buflen)) // Non-blocking

    {

int i;


        digitalWrite(13, true); // Flash a light to show received good message

// Message with a good checksum received, dump it.


<span style="color: #cc6600;">for</span> (i = 0; i &lt; buflen; i++)



    {

        Serial.print(buf[i]);  // the received data is stored in buffer

        }

    Serial.println("");

     }

}
2

You failed to let us know …

what version of the DHT library you are using. The one I grabbed does not differentiate two sensors the way the one yours does.

All of this means I can not replicate your issues until I know what DHT lib you are using.

3

Adafruit… who else.

…looks like it is this one here. Sample here.

4

Turn it into a integer problem?

You can try to send the humidity value as a tupel of two int values. So then your float to char* problem turns into a int to char* problem.

There are several techniques to do that. A simple one is to take the truncated integer part of your humidity value into int A and the scaled floating part into int B. So a number like 1234.5678 turns into A: “1234” and B: “5678” (Scaling-Factor: 1000).

This two integers can be transmitted as two char* now.

 

Here is a transmitter code snippet:

const int FOUR_DIGITS = 4;

void loop()

{

    int fourDigitValue = 1234;

    char valueAsChar[FOUR_DIGITS];

    itoa(fourDigitValue,valueAsChar,10);

    vw_send((uint8_t *)valueAsChar, strlen(valueAsChar));

    vw_wait_tx(); // Wait until the whole message is gone

}

Here is a receiver code:

void loop()

{

    uint8_t buf[VW_MAX_MESSAGE_LEN];

    uint8_t buflen = VW_MAX_MESSAGE_LEN;

    if (vw_get_message(buf, &buflen)) // Non-blocking

    {

char* message = (char*)buf;

        int value = atoi(message);

Serial.println(value);

    }

}

…

 

This is my test setup.

RF315MHzTestSetupTwoArduino.jpg
RF315MHzTestSetupTwoArduino.jpg500×500 94.3 KB

5

Double Post. Sorry.

dev/null

6

I did a quick search for float to string arduino

The first hit I got suggested via a forum post that:

#include <stdlib.h>
dtostrf(FLOAT,WIDTH,PRECSISION,BUFFER);

7

The code which works

// User Gareth    https://www.robotshop.com/letsmakerobots/user/2941

// Project Node   https://www.robotshop.com/letsmakerobots/node/12394

// Remote transmitting Temparature and Humidity over RF Link to SerialMonitor

// DHT11 Sensor

#include  // library for RF RX/TX

#undef int

#undef abs

#undef double

#undef float

#undef round

#undef round


#include “DHT.h”

#define DHTPIN 4

#define DHTTYPE DHT11   // DHT 11 

DHT dht(DHTPIN, DHTTYPE);


float temp_c;

float humidity;

int packet = 0;

char charnum[10];


void setup()

{

//  Debug Serial.begin(38400); 

// Serial.println(“Starting up”);


// Initialise the IO and ISR

  vw_set_tx_pin(3);

  vw_set_ptt_inverted(true); // Required for DR3100

  vw_setup(2000);	 // Bits per sec

  dht.begin();

}


void loop()

{

byte error;

byte rh;

float humival_f;

float tempval_f;

float dew_point_f;

  

char str[15];

 

// Read values from the sensor

  float temp_c;

  float humidity;

  temp_c = dht.readTemperature();

  humidity = dht.readHumidity();


  char buff[30];

  sprintf(buff,"%c",255);

  const char msg0 = buff;

  vw_send((uint8_t )msg0, strlen(msg0)); // Send control character 

  vw_wait_tx(); // Wait until the whole message is gone


// Serial.print(“Temperature = “);

  serialPrintFloat(temp_c);

  sprintf(buff,”%cC “,223);

  const char msg1 = buff;

  vw_send((uint8_t )msg1, strlen(msg1));

  vw_wait_tx(); // Wait until the whole message is gone

// Serial.print(“C”);    

 

////////////////////////////////////////////////////////////////////////////////////////     

  sprintf(buff,”%c”,254);

  const char msg5 = buff;

  vw_send((uint8_t )msg5, strlen(msg5));

  vw_wait_tx(); // Wait until the whole message is gone

 

// Serial.print(" Rel Humidity = “);

  serialPrintFloat(humidity);

// Serial.print(”%");

  const char msg2 = "% ";

  vw_send((uint8_t )msg2, strlen(msg2));

  vw_wait_tx(); // Wait until the whole message is gone

 

  delay(1000);

}


void serialPrintFloat( float f){

  //Serial.print((int)f);

  itoa((int)f, charnum, 10);

  vw_send((uint8_t )charnum, strlen(charnum));

  vw_wait_tx(); // Wait until the whole message is gone

  // Serial.print(".");

  const char msg = “.”;

  vw_send((uint8_t )msg, strlen(msg));

  vw_wait_tx(); // Wait until the whole message is gone

 

  int temp = (f - (int)f) * 100;

  // Serial.print( abs(temp) );

  itoa(abs(temp), charnum, 10);

  vw_send((uint8_t )charnum, strlen(charnum));

  vw_wait_tx(); // Wait until the whole message is gone

}
8

Thats the Reciever Code

Guys, I set the SerialMonitor to 9600… and I got: 

ÿ23.0ßC þ35.0% defintly not what I expected ^^ Any idea how I can fix that?