About One Wire Protocol
One Wire is a serial device communication protocol designed by Dallas Semiconductor Corp. It uses a single wire for bi-directional communication. It is similar to I2C protocol that helps multiple devices communicate to the same bus but the difference is that one wire protocol has lower data rates and provides a longer range. Each device connected using One Wire protocol has a unique 64-bit serial number that is used to address the device. The least significant byte of the serial number is used to identify the type of the device. This avoids conflict when different types of devices are connected to the same bus using One Wire protocol.
One Wire devices work using 3 -5 Volts and the connection includes a single pull-up resister common to the One Wire bus. Normally the connection requires three wires, among which, two are used for powering up the device and one for data transmission but One Wire devices could even work with two wires, which include data and ground. In this case the device draws power from the data line and stores it in the inbuilt capacitor which powers the device while data line is active.
List of One Wire devices
- Digital thermometers
- Humidity
- RTC
- EEPROM
- Dual Channel Addressable Switch
- Battery Monitor
DS18B20 Digital Thermometer
The DS18B20 Digital Thermometer provides data over a 1-Wire interface. Now only one wire (and ground) needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and performing temperature conversions can be derived from the data line itself.
Projects with One Wire Protocol
One of the projects we worked using this needed integration of Raspberry Pi with Amazon Cloud. Here the device had to monitor temperature from different nodes and the derived data had to be transferred to the cloud. Considering the distance of communication, the number of interfacing lines required and the powering complexity we chose to use one wire protocol.
Other applications where this feature is useful include HVAC environmental controls, sensing temperatures inside buildings, equipment or machinery, and process monitoring and control. It is also available in water proof packages so that it can be used for measuring temperature of water and other non-reacting liquids in chemical process stations. Since it provides data in digital format one wire is more immune to noise and suitable for industrial application compared to analog devices.
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