OneWire DS18S20, DS18B20, DS1822 Temperature
DS18B20
The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central microprocessor. It has an operating temperature range of -55°C to +125°C and is accurate to ±0.5°C over the range of -10°C to +85°C. In addition, the DS18B20 can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply. 分辨率9-12位，可设置报警，适用于1-Wire 总线，测量温度-55-125摄氏度
Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18B20s distributed over a large area. Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment, or machinery, and process monitoring and control systems. 一个控制器可连接多个传感器，可应用于许多领域
FEATURES 特点
§ Unique 1-Wire® Interface Requires Only One Port Pin for Communication
§ Each Device has a Unique 64-Bit Serial Code Stored in an On-Board ROM
§ Multidrop Capability Simplifies Distributed Temperature-Sensing Applications
§ Requires No External Components
§ Can Be Powered from Data Line; Power Supply Range is 3.0V to 5.5V
§ Measures Temperatures from -55°C to +125°C (-67°F to +257°F)
§ ±0.5°C Accuracy from -10°C to +85°C
§ Thermometer Resolution is User Selectable from 9 to 12 Bits
§ Converts Temperature to 12-Bit Digital Word in 750ms (Max)
64-BIT LASERED ROM CODE 64位光刻ROM编码
Each DS18B20 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits of the ROM code contain the DS18B20’s 1-Wire family code: 28h（8位家族编码）. The next 48 bits contain a unique serial number（48位序列码）. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from the first 56 bits of the ROM code（8位冗余检验码）. A detailed explanation of the CRC bits is provided in the CRC Generation section. The 64-bit ROM code and associated ROM function control logic allow the DS18B20 to operate as a 1-Wire device using the protocol detailed in the 1-Wire Bus System section.
Figure 6. 64-Bit Lasered ROM Code
示例程序
1 #include <OneWire.h> 2 3 4 5 // OneWire DS18S20, DS18B20, DS1822 Temperature Example 6 7 // 8 9 // http://www.pjrc.com/teensy/td_libs_OneWire.html 10 11 // 12 13 // The DallasTemperature library can do all this work for you! 14 15 // http://milesburton.com/Dallas_Temperature_Control_Library 16 17 18 19 OneWire ds(10); // on pin 10，定义单总线设备ds，连接于10号引脚 20 21 22 23 void setup(void) 24 25 { 26 27 Serial.begin(9600); 28 29 } 30 31 32 33 void loop(void) 34 35 { 36 37 byte i; 38 39 byte present = 0; 40 41 byte type_s; 42 43 byte data[12]; 44 45 byte addr[8]; //传感器的ROM，共8个字节的数据，64位 46 47 float celsius, fahrenheit; 48 49 50 51 if ( !ds.search(addr)) //查询不到ds就一直查询 52 53 { 54 55 Serial.println("No more addresses."); 56 57 Serial.println(); 58 59 ds.reset_search(); 60 61 delay(250); 62 63 return; 64 65 } 66 67 68 69 Serial.print("ROM ="); //查询到则显示ds的地址 70 71 for( i = 0; i < 8; i++) 72 73 { 74 75 Serial.write(' '); 76 77 Serial.print(addr[i], HEX); 78 79 } 80 81 82 83 if (OneWire::crc8(addr, 7) != addr[7]) // CRC检验失败的情况 84 85 { 86 87 Serial.println("CRC is not valid!"); 88 89 return; 90 91 } 92 93 Serial.println(); 94 95 96 97 // the first ROM byte indicates which chip ，根据addr[0]决定DS18系列的型号 98 99 switch (addr[0]) 100 101 { 102 103 case 0x10: 104 105 Serial.println(" Chip = DS18S20"); // or old DS1820 106 107 type_s = 1; 108 109 break; 110 111 case 0x28: //0x28是DS18B20的家族编码 112 113 Serial.println(" Chip = DS18B20"); 114 115 type_s = 0; 116 117 break; 118 119 case 0x22: 120 121 Serial.println(" Chip = DS1822"); 122 123 type_s = 0; 124 125 break; 126 127 default: 128 129 Serial.println("Device is not a DS18x20 family device."); 130 131 return; 132 133 } 134 135 136 137 ds.reset(); //复位 138 139 ds.select(addr); // 选择设备 140 141 ds.write(0x44,1); 142 143 // start conversion, with parasite power on at the end， 144 145 //传感器内部温度变换保存在暂存器，0x44是传感器的协议编码 146 147 148 149 delay(1000); // maybe 750ms is enough, maybe not 150 151 // we might do a ds.depower() here, but the reset will take care of it. 152 153 154 155 present = ds.reset(); //返回1表示有设备存在 156 157 ds.select(addr); 158 159 ds.read(0xBE); // Read Scratchpad 读暂存器，0xBE是传感器的协议编码 160 161 162 163 Serial.print(" Data = "); 164 165 Serial.print(present,HEX); 166 167 Serial.print(" "); 168 169 for ( i = 0; i < 9; i++) 170 171 { // we need 9 bytes 172 173 data[i] = ds.read(); 174 175 Serial.print(data[i], HEX); 176 177 Serial.print(" "); 178 179 } 180 181 Serial.print(" CRC="); 182 183 Serial.print(OneWire::crc8(data, 8), HEX); 184 185 Serial.println(); 186 187 188 189 // convert the data to actual temperature 190 191 192 193 unsigned int raw = (data[1] << 8) | data[0]; 194 195 if (type_s) //DS18S20对应的温度转换 196 197 { 198 199 raw = raw << 3; // 9 bit resolution default 200 201 if (data[7] == 0x10) 202 203 { 204 205 // count remain gives full 12 bit resolution 206 207 raw = (raw & 0xFFF0) + 12 - data[6]; 208 209 } 210 211 } 212 213 else //DS18B20，DS1822对应的温度转换 214 215 { 216 217 byte cfg = (data[4] & 0x60); 218 219 if (cfg == 0x00) raw = raw << 3; // 9 bit resolution, 93.75 ms 220 221 else if (cfg == 0x20) raw = raw << 2; // 10 bit res, 187.5 ms 222 223 else if (cfg == 0x40) raw = raw << 1; // 11 bit res, 375 ms 224 225 // default is 12 bit resolution, 750 ms conversion time 226 227 } 228 229 celsius = (float)raw / 16.0; //摄氏温度 230 231 fahrenheit = celsius * 1.8 + 32.0; //华氏温度 232 233 Serial.print(" Temperature = "); 234 235 Serial.print(celsius); 236 237 Serial.print(" Celsius, "); 238 239 Serial.print(fahrenheit); 240 241 Serial.println(" Fahrenheit"); 242 243 }