Diferenta este de gama de masura cu precizie mare de +0,5 grade Celsius, care este la DS18B20 de la -10 pana la +85 grade Celsius, iar la MAX31820 de la +10 pana la +45 grade Celsius, pana si cei 8 biti de identificare ai familiei de senzori este identic 028h.
Prima data am conectat doar un senzor MAX31280 in paralel cu DS18B20, ca sa-i aflu adresa, folosind 2 sketch-uri, unul fin cel din exemplul de la libraria OneWire si celalalt in care masoara temperaturi si cu un LM35:
Am conectat si pe al doilea senzor MAX31820, folosind cele 2 sketch-uri si am obtinut:
Modul de conectare in paralel este prezentat, de exemplu, in articolul Temperature Sensing using DS18B20 Digital Sensors:
Primul sketch folosit, in care se folosesc doar senzorii DS1820, respectiv MAX31820, este cel clasic din exemplul de la libraria OneWire, cu mici modificari:
#include <OneWire.h>
// OneWire DS18S20, DS18B20, DS1822 Temperature Example
//
// http://www.pjrc.com/teensy/td_libs_OneWire.html
//
// The DallasTemperature library can do all this work for you!
// http://milesburton.com/Dallas_Temperature_Control_Library
OneWire ds(10); // on pin 10 (a 4.7K resistor is necessary)
void setup(void) {
Serial.begin(9600);
}
void loop(void) {
byte i;
byte present = 0;
byte type_s;
byte data[12];
byte addr[8];
float celsius, fahrenheit;
if ( !ds.search(addr)) {
Serial.println("No more addresses.");
Serial.println();
ds.reset_search();
delay(250);
return;
}
Serial.print("ROM =");
for( i = 0; i < 8; i++) {
Serial.write(' ');
Serial.print(addr[i], HEX);
}
if (OneWire::crc8(addr, 7) != addr[7]) {
Serial.println("CRC is not valid!");
return;
}
Serial.println();
// the first ROM byte indicates which chip
switch (addr[0]) {
case 0x10:
Serial.println(" Chip = DS18S20"); // or old DS1820
type_s = 1;
break;
case 0x28:
Serial.println(" Chip = DS18B20");
type_s = 0;
break;
case 0x22:
Serial.println(" Chip = DS1822");
type_s = 0;
break;
default:
Serial.println("Device is not a DS18x20 family device.");
return;
}
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, with parasite power on at the end
delay(3000); // maybe 750ms is enough, maybe not
// we might do a ds.depower() here, but the reset will take care of it.
present = ds.reset();
ds.select(addr);
ds.write(0xBE); // Read Scratchpad
Serial.print(" Data = ");
Serial.print(present, HEX);
Serial.print(" ");
for ( i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
Serial.print(data[i], HEX);
Serial.print(" ");
}
Serial.print(" CRC=");
Serial.print(OneWire::crc8(data, 8), HEX);
Serial.println();
// Convert the data to actual temperature
// because the result is a 16 bit signed integer, it should
// be stored to an "int16_t" type, which is always 16 bits
// even when compiled on a 32 bit processor.
int16_t raw = (data[1] << 8) | data[0];
if (type_s) {
raw = raw << 3; // 9 bit resolution default
if (data[7] == 0x10) {
// "count remain" gives full 12 bit resolution
raw = (raw & 0xFFF0) + 12 - data[6];
}
} else {
byte cfg = (data[4] & 0x60);
// at lower res, the low bits are undefined, so let's zero them
if (cfg == 0x00) raw = raw & ~7; // 9 bit resolution, 93.75 ms
else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
//// default is 12 bit resolution, 750 ms conversion time
}
celsius = (float)raw / 16.0;
fahrenheit = celsius * 1.8 + 32.0;
Serial.print(" Temperature = ");
Serial.print(celsius);
Serial.print(" Celsius, ");
Serial.print(fahrenheit);
Serial.println(" Fahrenheit");
Serial.println("-----------------------");
}
// original sketch from http://learn.adafruit.com/tmp36-temperature-sensor/using-a-temp-sensor
// adapted sketch by niq_ro from http://nicuflorica.blogspot.com
// LM35 datasheet: http://www.ti.com/lit/ds/symlink/lm35.pdf
// inspired by http://www.roroid.ro/wiki/pmwiki.php/Main/TermometruCuArduino
// OneWire DS18S20, DS18B20, DS1822 Temperature Example: http://www.pjrc.com/teensy/td_libs_OneWire.html
// The DallasTemperature library can do all this work for you!
// http://milesburton.com/Dallas_Temperature_Control_Library
#include <OneWire.h>
//LM35 Pin Variables
int sensorPin = 0; //the analog pin the LM35 Vout (sense) pin is connected to A0
//the resolution is 10 mV / degree centigrade with a
int diodePin = 1; //pin for measure voltage diode
/*
* setup() - this function runs once when you turn your Arduino on
* We initialize the serial connection with the computer
*/
// added part by niq_ro
float vmed = 0;
float ve = 0;
OneWire ds(10); // on pin 10 (a 4.7K resistor is necessary)
void setup()
{
Serial.begin(9600); //Start the serial connection with the computer
//to view the result open the serial monitor
}
void loop() // run over and over again
{
vmed = 0;
ve=0;
for (int j = 0; j < 10; j++) {
//getting the voltage reading from the temperature sensor
int reading = analogRead(sensorPin);
int reading1 = analogRead(diodePin);
// converting that reading to voltage, for 3.3v arduino use 3.3
float voltage = (reading - reading1) * 5.0;
voltage /= 1023.0;
vmed = vmed + voltage;
delay(200);
}
ve = vmed/10;
// print LM35 logo
Serial.println("--------------------");
Serial.print(" LM35: ");
/*
// print out the voltage
Serial.print(ve); Serial.println(" volts");
*/
// now print out the temperature
float temperatureC = ve * 100 ; //converting from 10 mv per degree
//to degrees (voltage) times 100)
Serial.print(temperatureC); Serial.println(" degrees C");
/*
// now convert to Fahrenheit
float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
Serial.print(temperatureF); Serial.println(" degrees F");
*/
Serial.println("----------------");
delay(1000); //waiting a second
// DS18B20 part
byte i;
byte present = 0;
byte type_s;
byte data[12];
byte addr[8];
float celsius, fahrenheit;
if ( !ds.search(addr)) {
Serial.println("No more addresses.");
Serial.println();
ds.reset_search();
delay(250);
return;
}
Serial.print("ROM =");
for( i = 0; i < 8; i++) {
Serial.write(' ');
Serial.print(addr[i], HEX);
}
if (OneWire::crc8(addr, 7) != addr[7]) {
Serial.println("CRC is not valid!");
return;
}
Serial.println();
// the first ROM byte indicates which chip
switch (addr[0]) {
case 0x10:
Serial.println(" Chip = DS18S20"); // or old DS1820
type_s = 1;
break;
case 0x28:
Serial.println(" Chip = DS18B20");
type_s = 0;
break;
case 0x22:
Serial.println(" Chip = DS1822");
type_s = 0;
break;
default:
Serial.println("Device is not a DS18x20 family device.");
return;
}
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, with parasite power on at the end
delay(1000); // maybe 750ms is enough, maybe not
// we might do a ds.depower() here, but the reset will take care of it.
present = ds.reset();
ds.select(addr);
ds.write(0xBE); // Read Scratchpad
Serial.print(" Data = ");
Serial.print(present, HEX);
Serial.print(" ");
for ( i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
Serial.print(data[i], HEX);
Serial.print(" ");
}
Serial.print(" CRC=");
Serial.print(OneWire::crc8(data, 8), HEX);
Serial.println();
// Convert the data to actual temperature
// because the result is a 16 bit signed integer, it should
// be stored to an "int16_t" type, which is always 16 bits
// even when compiled on a 32 bit processor.
int16_t raw = (data[1] << 8) | data[0];
if (type_s) {
raw = raw << 3; // 9 bit resolution default
if (data[7] == 0x10) {
// "count remain" gives full 12 bit resolution
raw = (raw & 0xFFF0) + 12 - data[6];
}
} else {
byte cfg = (data[4] & 0x60);
// at lower res, the low bits are undefined, so let's zero them
if (cfg == 0x00) raw = raw & ~7; // 9 bit resolution, 93.75 ms
else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
//// default is 12 bit resolution, 750 ms conversion time
}
celsius = (float)raw / 16.0;
fahrenheit = celsius * 1.8 + 32.0;
Serial.print("DS18B20: ");
Serial.print(celsius); Serial.println(" degrees C");
/*
Serial.print(fahrenheit); Serial.println(" degrees F");
*/
delay(2000);
}
Am facut si un mic filmulet, ca un rezumat, numit noii senzori MAX31820 fata de DS18B20
Daca se doreste conectarea doar a senzorilor digitali DS18B20 si/sau MAX31280 schema devine:
12.ian.2014
PS2: Am mai pus 2 filmulete (scuze pentru calitatea sunetului):- new MAX31820 vs DS18B20 and Arduino
PS2: Trebuie sa mentionez ceva, de care am uitat, in datasheet-ul senzorilor MAX31820, se mentioneaza ca tensiunea de alimentare normala este intre 3 si 3,7V deci ar functiona perfect cu microcontroler-e alimentate la tensiunea de 3,3V. Tot in datasheet se mentioneaza ca tensiunea maxima admisa este de 6V, exact ca la DS18B20... Eu le-am alimentat la 5V, cat era la Arduino si au mers perfect.
