LCD display: numbers in scientific notation

Projects Programming
1

Hello everyone,

I was wondering if anyone could suggest how to display a number in scientific notation on an LCD display.
My example code is below. My range of numbers to be displayed is from 1e-10 to 1e10, but as it is, my code cannot display that range.

Thank you for any suggestions !

#include <Wire.h>
#include <Adafruit_RGBLCDShield.h>
#include <utility/Adafruit_MCP23017.h>
#define GREEN 0x2
Adafruit_RGBLCDShield lcd = Adafruit_RGBLCDShield();
float sensorPin = A0;
int ledPin = 13;
float sensorValue = 0.00; // variable to store the value coming from the sensor
float Voltage;
float P;
void setup() {
pinMode(ledPin, OUTPUT);
}
void loop() {
// read the value from the sensor:
sensorValue = analogRead(sensorPin);
lcd.begin(16, 2);
lcd.print("P = ");
lcd.setBacklight(GREEN);
lcd.setCursor(0, 1);
Voltage=sensorValue5.00/1023.009.49;//Voltage calibration
P=pow(10.00,(Voltage*1.667-11.33));
lcd.print(P);
delay(10000);
}

3

The print() methods in the Print class (that the lcd class appears to derive from, though it is hard to tell, since you did not post a link to the library) do not do scientific notation.

The dtostrf() function converts a float/double to a string. The dtostre() function does the same, but in scientific notation format.

You can then print the string.

4

Delta_G:
sprintf has format specifier for scientific notation. You could make yourself a char array, fill it with sprintf, and print it to the LCD.

For floats?

6

Thank you all for your responses !

I tried suggestion from PaulS, using the dtostre(), but it turns the entire display into illegible characters (unlike dtostrf, which prints the same as just printing the float P).

Basically, I declared char Ps[40] and then printed Ps derived from: dtostre(P,7,2,Ps), but as I said, it doesn't work...

Any ideas ?

Thank you !

7

Any ideas ?

Post the revised code, using code tags ("</>" button).

8

Sorry, here is the revised code;
<#include <Wire.h>
#include <Adafruit_RGBLCDShield.h>
#include <utility/Adafruit_MCP23017.h>
#define GREEN 0x2
Adafruit_RGBLCDShield lcd = Adafruit_RGBLCDShield();
float sensorPin = A0;
int ledPin = 13;
float sensorValue = 0.00; // variable to store the value coming from the sensor
float Voltage;
static float P;
static char Ps[20];

void setup() {
pinMode(ledPin, OUTPUT);
}

void loop() {
// read the value from the sensor:
sensorValue = analogRead(sensorPin);
lcd.begin(16, 2);
lcd.print("P = ");
lcd.setBacklight(GREEN);
lcd.setCursor(0, 1);
Voltage=sensorValue5.00/1023.009.49;//Voltage calibration
Voltage = 6.00;
P=pow(10.00,(Voltage*1.667-11.33));
dtostre(P,7,2,Ps);
lcd.print(Ps);
delay(10000);
}/>

9

and now with code tags, please.

10

I think you may be way mis-using the dtostre() function.

char* dtostre ( double __val, char * __s, unsigned char __prec, unsigned char __flags )

I think it should be more like:
dtostre(P,Ps,DTOSTR_ALWAYS_SIGN | DTOSTR_UPPERCASE);
or leave out the "| DTOSR_UPPERCASE" if you want "e" instead of "E".

not sure what you expected with the ",7,2"

11

Hi Dan95,

yeah, this:

dtostre(P,Ps,DTOSTR_ALWAYS_SIGN,DTOSTR_UPPERCASE);

did it, THANK YOU !