Arduino Wire.h send double to lcd

Question

I'd like the double number 200.00 shown as 200.00 on my LCD screen.

For instance, when I pass just a number (int) like 40 to the LCD, it uses it as an ASCII code to show a character on the display.

Now I want to send a double to it and it should be displayed as a double.

#include <Wire.h>

void setup() {
   Wire.begin(0x63);
}


double f;
void loop() {

  f = 200.00;

  Wire.beginTransmission(0x63);
  Wire.write(byte(0x00));
  Wire.write(4); //HIDE CURSOR
  Wire.write(12); //CLEAR SCREEN
  Wire.write(13); //CURSOR 2nd LINE
  Wire.write("Frequenz: ");
  Wire.write(f); //<- How to do this?
  Wire.write("Hz");
  Wire.endTransmission();
}

Mikael Patel · Accepted Answer · 2016-08-26 17:42:58Z

The Arduino Wire class does only support write() of byte, string and vector of bytes. To write a double it must first be converted to a string. This can be done with the standard C library function dtostrf().

double f;

void loop() {
  char buf[10];

  f = 200.00;

  Wire.beginTransmission(0x63);
  Wire.write(byte(0x00));
  Wire.write(4); //HIDE CURSOR
  Wire.write(12); //CLEAR SCREEN
  Wire.write(13); //CURSOR 2nd LINE
  Wire.write("Frequenz: ");
  Wire.write(dtostrf(f, 0, 2, buf));
  Wire.write("Hz");
  Wire.endTransmission();
}

The class inherits from Print (via Stream) so that the overloaded member function print() for double can be used. In that case:

double f;

void loop() {
  f = 200.00;

  Wire.beginTransmission(0x63);
  Wire.write(byte(0x00));
  Wire.write(4); //HIDE CURSOR
  Wire.write(12); //CLEAR SCREEN
  Wire.write(13); //CURSOR 2nd LINE
  Wire.write("Frequenz: ");
  Wire.print(f);
  Wire.write("Hz");
  Wire.endTransmission();
}

Please note that the maximum number of bytes to write (between beginTransmission and endTransmission) is limited to 32 in the standard configuration of the Arduino core.

Cheers!

Edgar Bonet · Accepted Answer · 2016-08-26 15:41:02Z

1

Use Wire.print(), instead of Wire.write() which is intended only to output single bytes or byte arrays.

answered Aug 26, 2016 at 15:41

Edgar Bonet

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