====== lamaPLC: DS18B20 1-Wire Digital Thermometer ======
{{ :sensor:ds18b20_5.png?200|DS18B20 1-Wire Digital Thermometer}}
The DS18B20 digital thermometer offers 9-bit to 12-bit Celsius temperature readings and features an alarm function with nonvolatile, user-programmable upper and lower trigger points. It communicates via a [[com:basic_1wire|1-Wire]] bus that requires only one data line (and ground) to connect with a central microprocessor. Additionally, the DS18B20 can draw power directly from the data line, known as [[com:basic_1wire|"parasite power"]], eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, enabling multiple units to operate on the same 1-Wire bus. This makes it easy to control numerous DS18B20s with a single microprocessor across a large area.

This feature benefits applications such as HVAC environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and process monitoring and control systems.

===== Features =====
  * Unique [[com:basic_1wire|1-Wire]] interface requires only one port pin for communication. 
  * Multidrop capability simplifies distributed temperature sensing applications. 
  * It requires no external components and can be powered from a data line. 
  * The power supply range is **3.0V to 5.5V** DC. 
  * Zero standby power is required. 
  * It measures temperatures from **-55°C to +125°C**. The Fahrenheit equivalent is **-67°F to +257°F**. 
  * It offers ±0.5°C accuracy from -10°C to +85°C. 
  * Thermometer resolution is programmable from 9 to 12 bits. 
  * Converts 12-bit temperature to a digital word in 750 ms (max.). 
  * User-definable, nonvolatile temperature alarm settings are available. 
  * The alarm search command identifies and addresses devices whose temperature is outside the programmed limits (temperature alarm condition). 
  * Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system.

===== Wiring =====
|< 100%>|
|**Red wire:** Power supply (3.0V - 5.5V DC) \\ **Black wire:** GND \\ **Yellow wire:** Signal (1-wire bus) \\ |{{ :sensor:ds18b20_7.png?300|DS18B20 wiring}}|{{ :sensor:ds18b20_8.png?300|DS18B20 wiring}}|


===== Parasitic/normal mode DS18B20 /  1-wire bus =====
|< 100% 50% 50% >|
^Normal mode^Parasitic mode|
|{{:com:ds18b20_normal_mode.png|Normal mode by 1-wire bus}}|{{:com:ds18b20_parasite_mode.png|Parasitic mode by 1-wire bus}}|
|With an external supply, three wires are needed: the bus wire, ground, and power. The **4.7k pull-up resistor** remains necessary on the bus wire. Since the bus is available for data transfer, the microcontroller can continually check the device's status during conversion. This allows a conversion to complete as soon as the device reports it is done, without waiting for the conversion time (which depends on device function and resolution) in //"parasite"// power mode.|When operating in parasite power mode, it requires only two wires: one data wire and one ground wire. The power line must be connected to ground in this mode, as specified in the datasheet. A 4.7k pull-up resistor should be connected to the 1-wire bus at the controller. When the line is in a //"high"// state, the device pulls current to charge an internal component capacitor.|

===== Addressing a 1-Wire device =====
Each 1-Wire device has a unique 64-bit 'ROM' address, which includes an 8-bit family code, a 48-bit serial number, and an 8-bit CRC. The CRC helps verify the integrity of the data.

For example, the sample code below checks if the device being addressed is a DS18S20 temperature sensor by looking for its family code, 0x10. To use the sample code with the newer DS18B20 sensor, you would look for a family code of 0x28. For the DS1822, you would check for 0x22.

===== DS18B20 and Arduino =====
{{ :sensor:ds18b20_6.png?400 |DS18B20 and Arduino}}

With Arduino, multiple DS18B20 sensors can be connected to a 1-wire bus simultaneously. It is recommended to power the signal line with a 4.7 kΩ resistor from the 5V DC supply.

===== 1-wire topics on lamaPLC =====
{{topic>1-wire}}

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{{tag>DS18B20 sensor 1-wire communication Arduino Thermometer Parasitic_mode}}
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