Volt Meter & Temperature Monitor – Part 2

I was unhappy with the previous version of this project, which used a TMP36 analog temperature sensor. The output moved around alot, up to 5 degrees, and wouldn’t stabilize. I replaced it with my favorite, the DS18B20 digital sensor. Now I have rock solid temperature readings, rock solid voltage measurement, and everyone is happy.

Since my waterproof DS18B20 is already wired, I wanted to keep the leads together, so I wrote a LOW to D2 to make it the Gnd, and a HIGH to D6 to make it +5vdc to power the DS18B20. A 4.7k resistor goes between data (D3) and +5vdc (D6).

This version measure 0-29vac. To measure DC, remove bridge rectifier and capacitor.

Find the address of your DS18B20

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See the changes below:

#include “OneWire.h”
#include “DallasTemperature.h”
#include “LiquidCrystal.h”
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

// Data wire is plugged into pin 3 on the Arduino
#define ONE_WIRE_BUS 3

// 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);

DeviceAddress insideThermometer = { 0x28, 0x27, 0xB0, 0xBD, 0x04, 0x00, 0x00, 0xF0 };

int tempNegPin = 2; // Gnd for DS18B20
int tempPosPin = 6;  // +5vdc for DS18B20

int voltPin = 0;     // voltage divider (middle terminal) connected to analog pin 0
// outside leads to 0-29vac
int val = 0;           // variable to store the value read
int volt = 0;           // variable to store the voltage calculated

void setup(void)
{
// Used two unused digital ports as +5v and Gnd for the DS18B20
pinMode(tempPosPin, OUTPUT);      // sets the digital pin as output
pinMode(tempNegPin, OUTPUT);      // sets the digital pin as output
digitalWrite(tempPosPin, HIGH);       // sets digital pin to +5vdc
digitalWrite(tempNegPin, LOW);     // sets digital pin to Gnd

lcd.begin(20, 4);            // setup LCD

// Start up the library
sensors.begin();
// set the resolution to 10 bit (good enough?)
sensors.setResolution(insideThermometer, 10);

}

void printTemperature(DeviceAddress deviceAddress)
{
float tempC = sensors.getTempC(deviceAddress);
if (tempC == -127.00) {
lcd.setCursor(0, 2);
lcd.print(“Error getting”);
lcd.setCursor(0, 3);
lcd.print(“temperature”);

} else {
lcd.setCursor(0, 2);
lcd.print(“Temp “);
lcd.print((char)223);
lcd.print(“C: “);
lcd.print(tempC);
lcd.setCursor(0, 3);
lcd.print(“Temp “);
lcd.print((char)223);
lcd.print(“F: “);
lcd.print(DallasTemperature::toFahrenheit(tempC));

}
}

void loop(void)
{
delay(500);

val = analogRead(voltPin);    // read the input pin

volt = map(val, 0, 1023, 0, 29); // map 29v range

lcd.setCursor(0, 0);
lcd.print(“VAC  “);
if (volt<10 br=”” lcd.print=”(” nbsp=””>   lcd.print(volt);

sensors.requestTemperatures();

printTemperature(insideThermometer);

}

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