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 Chapter 8. Advanced Experiments 8.3. Experiment with 1-Wire Digital Thermometer DS18B20 The DS18B20 Digital Thermometer provides 9 to 12–bit centigrade 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. 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. Features: Unique 1-Wire interface requires only one port pin for communication Each device has a unique 64-bit serial code stored in an onboard 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.) User-definable nonvolatile (NV) alarm settings Alarm search command identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition) Available in 8-pin SO (150mil), 8-pin SOP, and 3-pin TO-92 packages Software compatible with the DS1822 Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system Software and Hardware Design with DS18B20This experiment illustrates the software and hardware interface between DS18B20 and MCU. MCU reads temperature from DS18B20, and display the result on LED display. Plug in the DS18B20 chip into the socket, and toggle on the function select to ‘18B20’ before using.
Schematic Diagram
Program Flow Chart
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