Difference between revisions of "DS18B20 1 - Wire Digital Thermometer Module"

Revision as of 02:24, 27 May 2014

Overview

DS18B20 is a single-bus digital temperature sensor with features of ultra-small size, wide range of applicable voltage and measurable temperature and high resolution, etc. , which can be applied to temperature control, industrial systems, consumer products, thermometers or any thermal measurement system.

Features

1. Plug and play, easy to use. Compatible with the mainstream 2.54 interfaces and 4-Pin Grove interfaces in the market.

2. With use of M4 standard fixed holes, compatible with M4-standard kits such as Lego and Makeblock.

3. Rotatable detecting direction for better adaption.

Specifications

Note 1: S for digital input/output port, V and G for voltage at the common collector and ground respectively

DC electrical characteristics

AC electrical characteristics

Instruction

Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus. The figure below shows a block diagram of DS18B20. The scratchpad memory contains the 2-byte temperature register that stores the datal output from the temperature sensor. In addition, the scratchpad provides access to direct temperature alarm trigger registers (TH and TL) and the 1-byte configuration register. The configuration register allows the user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile (EEPROM), so they will retain data when the device is powered down.

Demo

Connect S port of DS18B20 electronic brick to D0 port of Arduino board, and we will use the following program to read register information and temperature value.

 #include 

 // 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

 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(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

 unsigned int 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);
   if (cfg == 0x00) raw = raw << 3;  // 9 bit resolution, 93.75 ms
   else if (cfg == 0x20) raw = raw << 2; // 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");
 }

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