DS18B20 — Programmable Resolution 1-Wire Digital Thermometer

Overview

The DS18B20 is a 1-Wire digital temperature sensor manufactured by Maxim Integrated (now Analog Devices). It communicates over a single data line plus ground (1-Wire bus protocol), requiring only one microcontroller pin to interface with multiple sensors distributed over a large area.

Each DS18B20 has a unique 64-bit factory-lasered ROM ID code, allowing multiple DS18B20 sensors to coexist on the same 1-Wire bus. The sensor offers user-configurable measurement resolution from 9 to 12 bits (corresponding to $0.5\text{ }^\circ\text{C}$ down to $0.0625\text{ }^\circ\text{C}$ increments).

Quick reference


Operating voltage (`VDD`)	3.0 V – 5.5 V (Supports Parasite Power mode on `DQ`)
Measurement range	-55 °C to +125 °C (-67 °F to +257 °F)
Accuracy	$\pm 0.5\text{ }^\circ\text{C}$ (from -10 °C to +85 °C)
Resolution	Configurable 9, 10, 11, or 12 bits ( $0.5\text{ }^\circ\text{C}$ to $0.0625\text{ }^\circ\text{C}$ )
Interface	1-Wire (Dallas/Maxim single-wire serial interface)
Conversion time	93.75 ms (9-bit) to 750 ms (12-bit max)

Pinout

TO-92 Package & Waterproof Probe Cable

Pin / Wire Color	Name	Type	Description
1 (Left / Black)	`GND`	Power	Ground (0 V)
2 (Center / Yellow or White)	`DQ`	Digital I/O	1-Wire Data Input/Output (requires 4.7 kΩ pull-up to VDD)
3 (Right / Red)	`VDD`	Power	Optional external power supply (GND for parasite power mode)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	`VDD`	3.0	5.0	5.5	V	Local power mode
Standby Current	`DDS`	—	750	1000	nA	$V_{DD} = 5.0\text{ V}$
Active Current	`DD`	—	1.0	1.5	mA	During temperature conversion
Temperature Accuracy	$T_{acc}$	—	$\pm 0.5$	$\pm 2.0$	°C	$-10\text{ }^\circ\text{C}$ to $+85\text{ }^\circ\text{C}$
12-Bit Conversion Time	$t_{CONV}$	—	400	750	ms	12-bit resolution mode
DQ Pull-Up Resistor	$R_{PUP}$	1.5	4.7	10.0	kΩ	Bus pull-up resistor

1-Wire protocol & scratchpad commands

Communication with the DS18B20 follows a strict sequence:

Reset pulse & Presence detect (Master pulls DQ LOW for $\ge 480\text{ }\mu\text{s}$ , slave responds with presence pulse).
ROM Command (0xCC Skip ROM for single sensor, 0x55 Match ROM for multiple sensors).
Function Command (e.g. 0x44 Convert T, 0xBE Read Scratchpad).

Scratchpad memory map

The DS18B20 scratchpad consists of 9 bytes of SRAM:

Byte	Register	Description
0	`Temperature LSB`	Low byte of temperature value ( $2^{-4} = 0.0625\text{ }^\circ\text{C}/\text{LSB}$ )
1	`Temperature MSB`	High byte of temperature value (sign bits)
2	`TH Register`	High temperature alarm trigger byte (EEPROM backed)
3	`TL Register`	Low temperature alarm trigger byte (EEPROM backed)
4	`Configuration`	Resolution setting (Bits 6:5 — `00`: 9-bit, `01`: 10-bit, `10`: 11-bit, `11`: 12-bit)
5–7	`Reserved`	Factory reserved bytes
8	`CRC`	CRC byte calculated over bytes 0 through 7 ( $X^8 + X^5 + X^4 + 1$ )

Temperature formula

The 16-bit temperature register stores two's-complement temperature in increments of $0.0625\text{ }^\circ\text{C}$ :

$\text{Temperature }(^\circ\text{C}) = \frac{\text{Raw 16-bit Value}}{16}$

Wiring

Standard Local Power Setup

DS18B20	Microcontroller (Arduino / ESP32)	Notes
`GND` (Black)	`GND`	Ground
`DQ` (Yellow)	Digital GPIO Pin	Connected to GPIO; 4.7 kΩ pull-up resistor to $V_{DD}$
`VDD` (Red)	`3.3V` or `5V`	External Power Supply

Warning

A pull-up resistor (typically 4.7 kΩ) between the DQ data line and VDD is mandatory. Without this pull-up resistor, the 1-Wire bus remains floating and communication will fail completely.

Common mistakes

Missing 4.7 kΩ pull-up resistor: The 1-Wire bus is open-drain and cannot function without an external pull-up resistor connected between DQ and VDD.
Not waiting for conversion to complete: At 12-bit resolution, a temperature conversion takes up to 750 ms. Attempting to read the scratchpad before this delay completes returns stale or invalid data ( $85\text{ }^\circ\text{C}$ default power-on value).
Parasite power mode current starvation: When using parasite power mode (where VDD is tied to GND), the data line must be held strongly HIGH during conversion to supply sufficient current.

Notes

Power-On Reset Value: The DS18B20 scratchpad initializes to $+85\text{ }^\circ\text{C}$ (0x0550) upon power-up. If your software reads exactly $85.0\text{ }^\circ\text{C}$ , it usually indicates a power cycle occurred without issuing a new 0x44 Convert T command.