DS18B20(3)

💖 DS18B20 💖

bestie. sit down. we're talking about the DS18B20 — a Programmable Resolution 1-Wire Digital Thermometer — and its twin MAX31820, the Ambient Temperature Sensor. this is a page from the One-Wire File System manual, section 3 (library functions, for the uninitiated), and it's lowkey iconic. 🦋

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🎀 SYNOPSIS 🎀

Thermometer. that's the whole vibe. 🌡️

28 [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 |
temperature10 | temperature11 | temperature12 | latesttemp | die | power |
temphigh | templow | tempres | errata/die | errata/trim |
errata/trimblanket | errata/trimvalid | address | crc8 | id | locator |
r_address | r_id | r_locator | type ]]

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👑 FAMILY CODE 👑

28

that's it. that's the family code. she's 28 and she knows it. ✨

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✨ SPECIAL PROPERTIES ✨

power

read-only, yes-no

is the chip powered externally (=1) or parasitically from the data bus (=0)? the data bus really said "i got you, i'll feed you too." 💅

temperature

read-only, floating point

the measured temperature, at 12 bit resolution. accurate queen. 🔥

temperature9 temperature10 temperature11 temperature12

read-only, floating point

measured temperature at 9 to 12 bit resolution. there's a tradeoff here, bestie — time versus accuracy in the temperature measurement. pick your fighter. ⚖️

latesttemp

read-only, floating point

measured temperature at 9 to 12 bit resolution, depending on the resolution of the latest conversion on this chip. reading this node will never trigger a temperature conversion — it's just chillin', reporting what it already knows. intended for use in conjunction with /simultaneous/temperature. 🫶

fasttemp

read-only, floating point

equivalent to temperature9. short and sweet, no cap.

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🌡️ TEMPERATURE ALARM LIMITS 🌡️

when the device exceeds either the temphigh or templow temperature threshold, the device is in the alarm state, and it will show up in the alarm directory. this is genuinely such a convenient way to poll for temperatures that are unsafe, especially if simultaneous temperature conversion is being done. alarm bell goes off, you know. 🚨

units for the temperature alarms are in the same temperature scale that was set for temperature measurements.

temperature thresholds are stored in non-volatile memory and persist until changed — even if power is lost. she does not forget. periodt.

temphigh

read-write, integer

shows or sets the lower limit for the high temperature alarm state. yes, lower limit for the high alarm. that's just how it is, bestie. 🙈

templow

read-write, integer

shows or sets the upper limit for the low temperature alarm state. same energy, opposite direction.

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🔧 TEMPERATURE RESOLUTION DEFAULT VALUE 🔧

tempres

read-write, integer

the device employs a non-volatile memory to store the default temperature resolution (9, 10, 11 or 12 bits) that gets applied after power-up. super useful if you're doing simultaneous temperature conversions. reading this node gives you the value stored in the non-volatile memory. writing sets a new power-on resolution value. 💾

as a side effect, reading this node resets the temperature resolution used by simultaneous temperature conversions to its power-on value. it also affects the resolution value used by latesttemp, to scale the latest conversion value — so make sure to re-sample the temperature before accessing latesttemp after writing or reading the tempres value. do not skip this step, i am begging. 😭

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🧚 TEMPERATURE ERRATA 🧚

there's a whole group of obscure internal properties exposed to protect against a hardware defect in certain batches of the B7 die of some DS18x20 chips. see http://www.1wire.org/en-us/pg_18.html or request AN247.pdf from Dallas directly. the lore runs deep. 💀

errata/die

read-only, ascii

two character manufacturing die lot: "B6" "B7" or "C2".

errata/trim

read-write, unsigned integer

32 bit trim value in the EEPROM of the chip. when written, it does not seem to read back. used for a production problem in the B7 die.

read allowed for all chips. only the B7 chips can be written.

errata/trimblanket

read-write, yes-no

writing non-zero (=1) puts a default trim value in the chip. only applied to the B7 die. reading will be true (non-zero) if the trim value is the blanket value. again, only B7 chips will register true, and since the written trim values cannot be read, this value may have little utility. honestly? she's giving mysterious. 🎀

errata/trimvalid

read-only, yes-no

is the trim value in the valid range? non-zero if true, which includes all non-B7 chips. slay.

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🌈 STANDARD PROPERTIES 🌈

address

r_address

read-only, ascii

the entire 64-bit unique ID. given as upper case hexadecimal digits (0-9A-F).

address starts with the family code.

r_address is the address in reverse order, which is often used in other applications and labeling. she contains multitudes, forwards and backwards. 🔄

crc8

read-only, ascii

the 8-bit error correction portion. uses cyclic redundancy check. computed from the preceding 56 bits of the unique ID number. given as upper case hexadecimal digits (0-9A-F).

family

read-only, ascii

the 8-bit family code. unique to each type of device. given as upper case hexadecimal digits (0-9A-F).

id

r_id

read-only, ascii

the 48-bit middle portion of the unique ID number. does not include the family code or CRC. given as upper case hexadecimal digits (0-9A-F).

r_id is the id in reverse order, which is often used in other applications and labeling.

locator

r_locator

read-only, ascii

uses an extension of the 1-wire design from iButtonLink company that associated 1-wire physical connections with a unique 1-wire code. if the connection is behind a Link Locator, the locator will show a unique 8-byte number (16 character hexadecimal) starting with family code FE. if no Link Locator is between the device and the master, the locator field will be all FF.

r_locator is the locator in reverse order.

present (DEPRECATED)

read-only, yes-no

is the device currently present on the 1-wire bus?

deprecated, bestie. she's retired. respect the elders but don't build on them. 💀

type

read-only, ascii

part name assigned by Dallas Semi. e.g. DS2401. alternative packaging (iButton vs chip) will not be distinguished. she's not gonna clock the outfit change, sorry. 🙈

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📖 DESCRIPTION 📖

1-Wire

1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. the bus is a low-power low-speed low-connector scheme where the data line can also provide power. one wire doing the absolute most. ⚡

each device is uniquely and unalterably numbered during manufacture. there are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. more complex devices (like thermocouple sensors) can be built with these basic devices. there are also 1-wire devices that have encryption included. the range? unmatched. 💅

the 1-wire scheme uses a single bus master and multiple slaves on the same wire. the bus master initiates all communication. the slaves can be individually discovered and addressed using their unique ID.

bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs designed to make the 1-wire bus and its devices easily accessible. the underlying principle is to create a virtual filesystem, with the unique ID being the directory, and the individual properties of the device are represented as simple files that can be read and written. it's giving "everything is a file" and honestly it ate. 🍓

details of the individual slave or master design are hidden behind a consistent interface. the goal is to provide an easy set of tools for a software designer to create monitoring or control applications. there are some performance enhancements in the implementation, including data caching, parallel access to bus masters, and aggregation of device communication. still, the fundamental goal has been ease of use, flexibility and correctness rather than speed. main character priorities. 👑

DS18B20

the DS18B20 (3) is one of several available 1-wire temperature sensors. it is the replacement for the DS18S20 (3). alternatives are DS1822 (3) as well as temperature/voltage measurements in the DS2436 (3) and DS2438 (3). for truly versatile temperature measurements, see the protean DS1921 (3) Thermachron (3). protean!! versatile!! iconic!!

the MAX31820 is functionally identical to the DS18B20 except for it's voltage requirements.

the DS18B20 (3) can select between 4 resolutions. in general, high resolution is the best choice unless your application is truly time-constrained. go big or go home, that's the rule. 🔥

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🔍 ADDRESSING 🔍

all 1-wire devices are factory assigned a unique 64-bit address. this address is of the form:

• Family Code — 8 bits
• Address — 48 bits
• CRC — 8 bits

addressing under OWFS is in hexadecimal, of form:

01.123456789ABC

where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.

the dot is optional, and the CRC code can be included. if included, it must be correct. no wiggle room. the CRC does not play. 🫶

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📄 DATASHEET 📄

http://pdfserv.maxim-ic.com/en/ds/DS18B20.pdf

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👀 SEE ALSO 👀

Programs

owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

Configuration and testing

owfs (5) owtap (1) owmon (1)

Language bindings

owtcl (3) owperl (3) owcapi (3)

Clocks

DS1427 (3) DS1904 (3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)

ID

DS2401 (3) DS2411 (3) DS1990A (3)

Memory

DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3) DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3) DS28EC20 (3)

Switches

DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3) InfernoEmbedded (3)

Temperature

DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065 (3) EDS0066 (3) EDS0067 (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826 (3)

Humidity

DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)

Voltage

DS2450 (3)

Resistance

DS2890 (3)

Multifunction (current, voltage, temperature)

DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)

Counter

DS2423 (3)

LCD Screen

LCD (3) DS2408 (3)

Crypto

DS1977 (3)

Pressure

DS2406 (3) TAI8570 (3) EDS0066 (3) EDS0068 (3)

Moisture

EEEF (3) DS2438 (3)

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💾 AVAILABILITY 💾

http://www.owfs.org

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🌸 AUTHOR 🌸

Paul Alfille (paul.alfille@gmail.com)

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okay that's the whole thing, bestie, every single flag and file and number accounted for, i did not skip a crumb. this was an OWFS Manpage from 2003 — yes, 2003, vintage, retro, lowkey a relic — for DS18B20 (3). go forth and measure some temperatures. you got this. 🫶✨💜