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lamaPLC: 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 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 "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 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
| Red wire: Power supply (3.0V - 5.5V DC) Black wire: GND Yellow wire: Signal (1-wire bus) |  |  |
Parasitic/normal mode DS18B20 / 1-wire bus
| Normal mode | Parasitic mode |
|---|---|
 |  |
| 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
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
| Page | Date | Tags |
|---|---|---|
| 2025/05/31 21:56 | 1-wire, communication, bus, microlan, i2c, uart, usart, ds18b20 | |
| 2025/09/23 21:03 | 1-wire, communication, bus, xml, iec 61850, iec, ethernet, scl, goose, ied | |
| 2025/10/09 20:52 | ds18b20, sensor, 1-wire, communication, arduino, thermometer, parasitic mode |
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