I am trying to publish the temperature value as follows
float h = dht.getHumidity();
float t = dht.getTempCelcius();
client.publish("myPiVal", t );
but get error at line client.publish
How can I convert the float value to string ?
Thanks
Hi,
try using String(t)
for example, I have:
Spark.publish("Humidity", "Measured humidity as: " + String(h));
from my own humidity sensor project (you might like to take a peek at: https://github.com/Tinamous/HumidityMonitor as it appears we might be doing something similar!)
Spark.publish(“Humidity”, "Measured humidity as: " + String(h)); Works , but the same logic does not work in below code.
client.publish(“myPiVal”, “Temprature :” + String(h) );
I am actually trying to Publish it to broker using MQQT.
Here relevant code
#include "Adafruit_DHT/Adafruit_DHT.h"
#include "MQTT/MQTT.h"
#define DHTPIN 2 // what pin we're connected to
// Uncomment whatever type you're using!
#define DHTTYPE DHT11 // DHT 11
void callback(char* topic, byte* payload, unsigned int length);
int lightLevel = 0;
DHT dht(DHTPIN, DHTTYPE);
MQTT client("brokerURL", 1883, callback);
// recieve message
void callback(char* topic, byte* payload, unsigned int length) {
char p[length + 1];
memcpy(p, payload, length);
p[length] = NULL;
String message(p);
if (message.equals("1"))
client.publish("myPiVal","Received 1"); // this publish works
else
client.publish("myPiVal","Did not receive"); // this publish works
}
void setup() {
// connect to the server
client.connect("broker url");
dht.begin();
// publish/subscribe
if (client.isConnected()) {
client.publish("myPiVal","Initating ....");
client.subscribe("MyEvent");
}
}
void loop() {
if (client.isConnected())
{
static char tempstr[15];
float h = dht.getHumidity();
float t = dht.getTempCelcius();
// Spark.publish("Temprature", "Measured Temprature is: " + String(t));
// Spark.publish("Humidity", "Measured Humidity is: " + String(h));
client.publish("myPiVal", "Temprature :" + String(h) ); //this line creates error
delay(4000);
client.loop();
}
}
Find attached the error screen shot. Any help is greatly appreciated.
Sorry. #SteveFail didn’t realise you were using MQTT, that makes it a bit more painful as you need a char[] going through.
Have a look at: http://stackoverflow.com/questions/7383606/converting-an-int-or-string-to-a-char-array-on-arduino
You might also like to look at one of my Arduino MQTT projects which may help with other MQTT things: https://github.com/Tinamous/DeckLights
To get you up and running give this a try (sorry it’s a little hacked as I don’t have the DHT):
float h = 23.4454;
float t = 27.557345464;
//float h = dht.getHumidity();
//float t = dht.getTempCelcius();
// Use String to convert the float to a string - theirs probably a better way but this is easy.
String temperatureString = "Temperature: " + String(t);
// You might be able to fix this rather than allocate a new char[] every time.
int length = temperatureString.length();
char temperature[length];
// Convert the string to char[]
temperatureString.toCharArray(temperature, temperatureString.length());
client.publish("myPiVal", temperature);Thanks a ton. This did the trick. However I had to change
temperatureString.length() to
temperatureString.length() + 1 in
// Convert the string to char[]
temperatureString.toCharArray(temperature, temperatureString.length());
as it was truncating the last character. Thanks Again.
Just a quick question…
If I want to convert the part of changing float to required format before publishing , how should the function look…
so that I can use it as
client.publish("myPiVal", ConvertIntString(2.23));
the below function gives error
char [] ConvertIntString(float intValue){
//String temperatureString = String(tempInFer);
String temperatureString = String(intValue);
int length = temperatureString.length();
char temperature[length];
temperatureString.toCharArray(temperature, temperatureString.length() + 1);
// return temperature;
}
You can also use this (shorter):
float f = 3.1415927;
char buf[10]; // Put whatever length you need here
String(f).toCharArray(buf,10);Some things to note:
Unfortunately, there does not appear to be a way to indicate that you want a particular number of decimal places in this method.
The dtoa() function appears not to be available in the local IDE, nor is dtostrf(). At least in the version I downloaded on July 24, sprintf with %f does not work (silently renders empty field). The cloud IDE does not appear to be working at the moment (compile attempts result in a 404 error message).
The general prototype for dot appears to be as follows:
dtoa(floating_point_value, mode (you probably want mode 0), decimal_digits, &decpt, &sign, **result)
I wasn’t able to find any real documentation for &decpt, &sign, or the format of **destination. It appears that these are actually return values. (decpt and sign are (uint8_t *) and specify the place for the function to place those values, whatever they are and result is type (char **) such that the function dynamically allocates a char[] to hold the result and then places a pointer to that in the location specified by result. (*result[0] = first character of result).
For your proposed function, try this:
char * ConvertIntString(float Value) {
String vString = String(Value);
int length = vString.length() + 1; // +1 allows room for trailing NULL
char *result = malloc(length * sizeof(char)); // the sizeof here isn't really
// necessary for char, but for
// portability...
vString.toCharArray(result, length);
return result;
}