Rounding to one decimal place when using OneWire, Dallastemperature, and LCD

Projects Programming
1

I have some code that does what I want it to do except round to one decimal place when displayed on my LCD screen. Does anyone have any suggestions? The code is listed below. Thanks in advance!

// DS18B20 2 sensors with LCD

// This Arduino sketch reads DS18B20 "1-Wire" digital
// temperature sensors.
// Tutorial:
// Arduino 1-Wire Tutorial

#include <OneWire.h>
#include <DallasTemperature.h>B20
#include <LiquidCrystal.h>
#include <SPI.h>

// Connections:
// rs (LCD pin 4) to Arduino pin 12
// rw (LCD pin 5) to Arduino pin 11
// enable (LCD pin 6) to Arduino pin 10
// LCD pin 15 to Arduino pin 13
// LCD pins d4, d5, d6, d7 to Arduino pins 5, 4, 3, 2
LiquidCrystal lcd(12, 11, 10, 5, 4, 3, 2);

int backLight = 13; // pin 13 will control the backlight

// Data wire is plugged into pin 8 on the Arduino
#define ONE_WIRE_BUS 8

// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature.
DallasTemperature sensors(&oneWire);

// Assign the addresses of your 1-Wire temp sensors.
// See the tutorial on how to obtain these addresses:
// http://www.hacktronics.com/Tutorials/arduino-1-wire-address-finder.html

DeviceAddress roomTemp = {
0x28, 0x9C, 0x99, 0x26, 0x04, 0x00, 0x00, 0x71 };
DeviceAddress ductTemp = {
0x28, 0xE3, 0xC5, 0xAF, 0x04, 0x00, 0x00, 0x33 };

void setup(void)
{
// Start up the library
sensors.begin();
// set the resolution to 10 bit (good enough?)
sensors.setResolution(roomTemp, 10);
sensors.setResolution(ductTemp, 10);

pinMode(backLight, OUTPUT);
digitalWrite(backLight, HIGH); // turn backlight on. Replace 'HIGH' with 'LOW' to turn it off.
lcd.begin(16,2); // columns, rows. use 16,2 for a 16x2 LCD, etc.
lcd.clear(); // start with a blank screen
}

void printTemperature(DeviceAddress deviceAddress)
{
float tempC = sensors.getTempC(deviceAddress);
if (tempC == -127.00) {
lcd.print("Error");
}

else {
tempC=tempC*1.8+32;
lcd.print(tempC);
lcd.print("/");
lcd.print(DallasTemperature::toFahrenheit(tempC));
}
}

void loop(void)
{
delay(6000);
sensors.requestTemperatures();
lcd.setCursor(0,0);
lcd.print("Room Temp: ");
printTemperature(roomTemp);
lcd.setCursor(0,1);
lcd.print("Duct Temp: ");
printTemperature(ductTemp);
}

2

If you look at the LiquidCrystal library, you'll see that the class derives from Print. So, the lcd.print() method is actually the Print::print() method. It you look at the documentation for the print() method, you'll see that it sometimes takes a second argument. For the method that prints floats, the second argument defines the number of decimal places desired.

3

I tried it like this and it did not work. I also tried it with putting the ,1 after each tempC still no dice. Any other suggestions?

// DS18B20 2 sensors with LCD

// This Arduino sketch reads DS18B20 "1-Wire" digital
// temperature sensors.
// Tutorial:
// Arduino 1-Wire Tutorial

#include <OneWire.h>
#include <DallasTemperature.h>B20
#include <LiquidCrystal.h>
#include <SPI.h>

// Connections:
// rs (LCD pin 4) to Arduino pin 12
// rw (LCD pin 5) to Arduino pin 11
// enable (LCD pin 6) to Arduino pin 10
// LCD pin 15 to Arduino pin 13
// LCD pins d4, d5, d6, d7 to Arduino pins 5, 4, 3, 2
LiquidCrystal lcd(12, 11, 10, 5, 4, 3, 2);

int backLight = 13; // pin 13 will control the backlight

// Data wire is plugged into pin 8 on the Arduino
#define ONE_WIRE_BUS 8

// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(ONE_WIRE_BUS);

// Pass our oneWire reference to Dallas Temperature.
DallasTemperature sensors(&oneWire);

// Assign the addresses of your 1-Wire temp sensors.
// See the tutorial on how to obtain these addresses:
// Arduino 1-Wire Address Finder

DeviceAddress roomTemp = {
0x28, 0x9C, 0x99, 0x26, 0x04, 0x00, 0x00, 0x71 };
DeviceAddress ductTemp = {
0x28, 0xE3, 0xC5, 0xAF, 0x04, 0x00, 0x00, 0x33 };

void setup(void)
{
// Start up the library
sensors.begin();
// set the resolution to 10 bit (good enough?)
sensors.setResolution(roomTemp, 10);
sensors.setResolution(ductTemp, 10);

pinMode(backLight, OUTPUT);
digitalWrite(backLight, HIGH); // turn backlight on. Replace 'HIGH' with 'LOW' to turn it off.
lcd.begin(16,2); // columns, rows. use 16,2 for a 16x2 LCD, etc.
lcd.clear(); // start with a blank screen
}

void printTemperature(DeviceAddress deviceAddress)
{
float tempC = sensors.getTempC(deviceAddress);
if (tempC == -127.00) {
lcd.print("Error");
}

else {
tempC=tempC*1.8+32;
lcd.print(tempC,1);
lcd.print("/");
lcd.print(DallasTemperature::toFahrenheit(tempC));
}
}

void loop(void)
{
delay(6000);
sensors.requestTemperatures();
lcd.setCursor(0,0);
lcd.print("Room Temp: ");
printTemperature(roomTemp);
lcd.setCursor(0,1);
lcd.print("Duct Temp: ");
printTemperature(ductTemp);
}

4

I tried it like this and it did not work.

Well, that makes it easy to help you. Something happened when you ran that code. You haven't told us what!

   tempC=tempC*1.8+32;

The value, in degrees Celsius, returned by the sensor, when multiplied by 1.8 and incremented by 32 is now a temperature in degrees Fahrenheit. Why are you storing that in tempC?

Why are you then passing the Fahrenheit temperature to a function that converts the temperature from Celsius to Fahrenheit?

5

Thank you PaulS! You made my day by pointing in the right direction.
It works for Serial.print as well.
I searched a day until I found this post. Just in case someone else lands on this old post:

void printTemperature(DeviceAddress deviceAddress)
{
float tempC = sensors.getTempC(deviceAddress);
if (tempC == -127.00) {
Serial.print("Error getting temperature");
} else {
Serial.print("C: ");
Serial.print(tempC,1); // The 1 behind the tempC (second argument) defines the numbers of digits required
}
}

6

It may just be that it's only been documented in the last eighteen months (I doubt it) but it's documented here.