DS18B20+: The Legendary Sensor That Conquered Temperature Measurement with One Wire

In the vast universe of temperature sensors, Analog Devices' (formerly Maxim Integrated) DS18B20+ is undoubtedly the brightest star. This digital temperature sensor, featuring the ingenious 1-Wire single-bus interface, completes both power delivery and communication using just a single data line - completely revolutionizing the wiring logic of traditional temperature measurement. It has become the "national-level" sensor of choice for industrial control, environmental monitoring, and smart home applications.

Core Specifications at a Glance

Parameter	Specification
Temperature Range	-55°C ~ +125°C
Accuracy	±0.5°C (-10°C ~ +85°C)
Resolution	9~12 bits programmable (up to 0.0625°C)
Supply Voltage	3.0V ~ 5.5V
Communication Protocol	1-Wire single bus
Package Types	TO-92 / SOIC-8 / µSOP-8
Unique ID	64-bit laser ROM serial number

Resolution vs. Conversion Time:

Resolution Precision	Max Conversion Time
9-bit	0.5°C 93.75ms
10-bit	0.25°C 187.5ms
11-bit	0.125°C 375ms
12-bit	0.0625°C 750ms

Q&A

Q: Why does the DS18B20+ only need one wire?
A: Because it uses the 1-Wire protocol. The DQ data line serves double duty - carrying both communication signals and parasitic power. During high-level pulses, the internal capacitor charges; during low-level pulses, it discharges to power the chip. No separate power pin is needed.

Q: How do multiple sensors coexist on the same wire without conflict?
A: Each DS18B20+ has a globally unique 64-bit ROM serial number. The host identifies each device individually using the SEARCH ROM (0xF0) command, enabling multi-drop networking with theoretically dozens of sensors on one bus.

Q: What if readings always show +85°C or -127°C?
A: +85°C is the power-on default; -127°C indicates a communication failure. Common causes include: forgetting to send CONVERT T (0x44) to start conversion, missing the 4.7kΩ pull-up resistor on the data line, or insufficient current in parasitic power mode.

The DS18B20+ supports both external power and parasitic power modes. While parasitic mode saves a wire, current draw during temperature conversion can reach 1.5mA - so multiple sensors in parallel require a MOSFET strong pull-up solution. For cable runs exceeding 50 meters, shielded twisted pair is recommended, as ordinary signal wires are prone to interference-induced data errors.

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