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Arduino CI Arduino-lint JSON check GitHub issues

License: MIT GitHub release PlatformIO Registry

DS18B20

Arduino library for the DS18B20 sensor - restricted to one sensor per pin.

Arduino Temperature Control Library (ATCL)

This DS18B20 library is not a full featured library for the DS18B20 family. This library supports only one DS18B20 per Arduino/ MCU pin.

If you need more functions or control over the DS18B20 family I refer to the library of Miles Burton - https://github.com/milesburton/Arduino-Temperature-Control-Library

I'm a great fan of the above library however some time ago I needed to strip it down to save a few dozen bytes. I reworked that minimalistic version into a library and I added a number of Arduino examples to help you get started.

Effort has been taken to keep the code, variables and function names compatible with ATCL library mentioned above. This way you can step over to that one with relatively few problems when you need more functionality like multiple sensors on one pin.

Finally this library will probably make it easier to use a DS18B20 with processing boards or IC's with small memory footprint.

Footprint OneWire

This library depends (is build) upon the OneWire library of Paul Stoffregen.

In issue #31 the footprint of the OneWireNG seems to be smaller when build on platformIO.

So if you are in need to save some more bytes, you might try [OneWireNG] (https://github.com/pstolarz/OneWireNg).

Related

This library is related to

Dependency

Interface

#include "DS18B20.h"

Constructor

The DS18B20 library supports only the DS18B20, only one sensor per pin, no parasite mode, no Fahrenheit and no alarm functions. The only feature the class supports is the asynchronous reading of the temperature by means of three core functions:

  • DS18B20(OneWire * ow, uint8_t resolution = 9) constructor needs a reference to OneWire object. Also sets the resolution, default to 9 bits.
  • bool begin(uint8_t retries = 3) resets oneWire and set resolution default to 9 bit.
    Returns true if all is OK. There will be a number of retries to connect, default 3.
  • bool isConnected(uint8_t retries = 3) resets oneWire checks if a device can be found.
    Returns true if a device is found. There will be a number of retries to connect, default 3.
  • bool getAddress(uint8_t * buf) returns true if the sensor is configured (available). Buf must be a byte array of at least 8 bytes.

Request Temperature

  • void requestTemperatures() trigger temperature conversion.
  • bool isConversionComplete() check if conversion is complete.
  • float getTempC(bool checkConnect = true) returns temperature in Celsius.
    • -127 = DEVICE_DISCONNECTED (only when checkConnect == true)
    • -128 = DEVICE_CRC_ERROR
    • can be faster by setting checkConnect to false. (experimental)
  • float getTempF() simple wrapper, returns temperature in Fahrenheit.

This "async only" allows the class to be both minimal in size and non-blocking. In fact the class has no support for a synchronous read in one call. This choice will teach people how to work in a non-blocking way from the start.

Offset

  • void setOffset(float offset = 0) set a (small) offset to calibrate the sensor.
  • float getOffset() return the current offset, default 0.

One additional application of the offset is to setOffset(273.15) which converts the default Celsius temperature into Kelvin.

Resolution

  • bool setResolution(uint8_t resolution = 9) resolution = 9..12 (9 is default). Returns false if no device is found.
  • uint8_t getResolution() return resolution set.

Configuration

  • void setConfig(uint8_t config) set DS18B20_CLEAR or DS18B20_CRC. If DS18B20_CRC flag is set the library will check the CRC, otherwise it won't. Not checking the CRC is a few milliseconds faster.
  • uint8_t getConfig() get current configuration
    • 1 == DS18B20_CRC
    • 0 == no flag set.

Operation

This library supports only one DS18B20 per Arduino/ MCU pin.

    //  BOTTOM VIEW
    //
    //          PIN  MEANING
    //   /---+
    //  /  o |  1    GND
    //  |  o |  2    DATA
    //  \  o |  3    VCC
    //   \---+

(always check datasheet)

Connect a pull-up resistor 4.7 KOhm between pin3 and pin2. When the wires are longer this resistor needs to be smaller.

-127 and 85

Two specific return values from reading the sensor:

  • minus 127 == DEVICE_DISCONNECTED
  • plus 85 is the power on default. If you get this unexpected it may indicate a power problem

Disconnect

During tests with DS18B20_test_disconnect.ino I noticed:

  • set resolution to 9 bits + disconnected data line ==> sensor blocks and keeps 9 bits resolution.
  • set resolution to 9 bits + disconnected VCC line ==> sensor stops and restarts at 12 bits resolution.
  • set resolution to 9 bits + disconnected GND line ==> sensor keeps running at 9 bits resolution.

Pull up resistor

An indicative table for pull up resistors, (E12 series), to get started.

Note: thicker wires require smaller resistors (typically 1 step in E12 series)

Length 5.0 Volt 3.3 Volt Notes
10cm (4") 10K0 6K8 might work without
20cm (8") 8K2 4K7
50cm (20") 4K7 3K3
100cm (3'4") 3K3 2K2
200cm (6'8") 2K2 1K0
500cm (16'8") 1K0 *
longer * *

* = no info, smaller?

Diagnosis notes

It was noted that the library sometimes give unexpected values, and keep sending these values.

This is due to the fact that by default the CRC is not checked to speed up reading. In fact, default only the two temperature registers are read. By setting sensor.setConfig(DS18B20_CRC); the whole scratchpad is read and the CRC can be checked.

table of known "strange values" and actions one could take. It is meant to start some diagnosis.

value possible cause optional action
0.0000 data line has no pull up use pull up
-0.0625 data line is constantly pulled HIGH check GND
-128 CRC error wrong pull up, bad sensor ?
-127 DISCONNECTED check wires }

If a value occurs only once in a while, wiring is often the cause, or it can be caused by e.g. induction e.g. switching on a motor while sensor is read.

Credits

Miles Burton who originally developed the Arduino Temperature Control Library. and all people who contributed to that library.

Future

Must

  • elaborate performance connected state.

Should

  • investigate performance gain of no CRC.
    • add performance table in readme.md
  • Extend oneWireSearch with device types
    • see oneWireScanner.ino (2016 version)
  • should checkConnect be a config flag like CRC?

Could

Wont

  • unit tests
    • get it working is too time consuming.

Support

If you appreciate my libraries, you can support the development and maintenance. Improve the quality of the libraries by providing issues and Pull Requests, or donate through PayPal or GitHub sponsors.

Thank you,