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195 lines
6.8 KiB
Markdown
195 lines
6.8 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DS18B20_RT/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/DS18B20_RT/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/DS18B20_RT/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DS18B20_RT/releases)
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# DS18B20
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Arduino library for the DS18B20 sensor - restricted to one sensor per pin.
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## Arduino Temperature Control Library (ATCL)
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This DS18B20 library is not a full featured library for the DS18B20 family.
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This library supports only one DS18B20 per Arduino/ MCU pin.
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If you need more functions or control over the DS18B20 family I refer to the library
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of Miles Burton - https://github.com/milesburton/Arduino-Temperature-Control-Library
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I'm a great fan of the above library however some time ago I needed to strip it down
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to save a few dozen bytes. I reworked that minimalistic version into a library and I
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added a number of Arduino examples to help you get started.
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#### Related
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This library is related to
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- https://github.com/RobTillaart/DS18B20_INT
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- https://github.com/milesburton/Arduino-Temperature-Control-Library
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## Interface
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```cpp
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#include "DS18B20.h"
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```
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#### Core
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The DS18B20 library supports only the DS18B20, only one sensor per pin, no parasite
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mode, no Fahrenheit and no alarm functions. The only feature the class supports is
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the asynchronous reading of the temperature by means of three core functions:
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- **DS18B20(OneWire \* ow, uint8_t resolution = 9)** constructor needs a reference to OneWire object.
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Also sets the resolution, default to 9 bits.
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- **bool begin(uint8_t retries = 3)** resets oneWire and set resolution default to 9 bit.
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Returns true if all is OK.
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There will be a number of retries to connect, default 3.
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- **bool isConnected(uint8_t retries = 3)** resets oneWire checks if a device can be found.
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Returns true if a device is found.
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There will be a number of retries to connect, default 3.
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- **void requestTemperatures()** trigger temperature conversion.
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- **bool isConversionComplete()** check if conversion is complete.
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- **float getTempC()** returns temperature in Celsius.
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- -127 = DEVICE_DISCONNECTED
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- -128 = DEVICE_CRC_ERROR
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- **bool setResolution(uint8_t resolution = 9)** resolution = 9..12 (9 is default).
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Returns false if no device is found.
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- **uint8_t getResolution()** return resolution set.
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- **bool getAddress(uint8_t \* buf)** returns true if the sensor is configured (available).
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Buf must be a byte array of at least 8 bytes.
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This "async only" allows the class to be both minimal in size and non-blocking.
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In fact the class has no support for a synchronous read in one call.
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This choice will teach people how to work in a non-blocking way from the start.
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Effort has been taken to keep the code, variables and function names compatible with
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ATCL library mentioned above. This way you can step over to that one with relatively
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few problems when you need more functionality like multiple sensors on one pin.
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Finally this library will probably make it easier to use a DS18B20 with processing
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boards or IC's with small memory footprint.
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#### Config
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- **void setConfig(uint8_t config)** set DS18B20_CLEAR or DS18B20_CRC.
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If DS18B20_CRC flag is set the library will check the CRC, otherwise it won't.
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Not checking the CRC is a few milliseconds faster.
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- **uint8_t getConfig()** get current configuration
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- 1 == DS18B20_CRC
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- 0 == no flag set.
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## Operation
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This library supports only **one** DS18B20 per Arduino/ MCU pin.
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```
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// BOTTOM VIEW
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//
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// PIN MEANING
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// /---+
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// / o | 1 GND
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// | o | 2 DATA
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// \ o | 3 VCC
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// \---+
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```
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(always check datasheet)
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Connect a pull-up resistor 4.7 KOhm between pin3 and pin2.
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When the wires are longer this resistor needs to be smaller.
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#### -127 and 85
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Two specific return values from reading the sensor:
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- minus 127 == DEVICE_DISCONNECTED
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- plus 85 is the power on default.
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If you get this unexpected it may indicate a power problem
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#### Disconnect
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During tests with **DS18B20_test_disconnect.ino** I noticed:
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- set resolution to 9 bits + disconnected data line ==> sensor blocks and keeps 9 bits resolution.
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- set resolution to 9 bits + disconnected VCC line ==> sensor stops and restarts at 12 bits resolution.
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- set resolution to 9 bits + disconnected GND line ==> sensor keeps running at 9 bits resolution.
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#### Pull up resistor
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An **indicative** table for pull up resistors, (E12 series), to get started.
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Note: thicker wires require smaller resistors (typically 1 step in E12 series)
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| Length | 5.0 Volt | 3.3 Volt | Notes |
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|----------------:|------------:|-----------:|:--------|
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| 10cm (4") | 10K0 | 6K8 | might work without |
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| 20cm (8") | 8K2 | 4K7 |
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| 50cm (20") | 4K7 | 3K3 |
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| 100cm (3'4") | 3K3 | 2K2 |
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| 200cm (6'8") | 2K2 | 1K0 |
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| 500cm (16'8") | 1K0 | \* |
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| longer | \* | \* |
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\* = no info, smaller?
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#### Diagnosis notes
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It was noted that the library sometimes give unexpected values, and keep
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sending these values.
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This is due to the fact that by default the CRC is not checked to speed up reading.
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In fact, default only the two temperature registers are read.
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By setting ```sensor.setConfig(DS18B20_CRC);``` the whole scratchpad is read
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and the CRC can be checked.
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table of known "strange values" and actions one could take.
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It is meant to start some diagnosis.
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| value | possible cause | optional action |
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|:--------|:------------------------------------|:----------------|
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| 0.0000 | data line has no pull up | use pull up |
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| -0.0625 | data line is constantly pulled HIGH | check GND |
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| -128 | CRC error | wrong pull up, bad sensor ? |
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| -127 | DISCONNECTED | check wires }
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If a value occurs only once in a while, wiring is often the cause,
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or it can be caused by e.g. induction e.g. switching on a motor while
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sensor is read.
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## Credits
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Miles Burton who originally developed the Arduino Temperature Control Library.
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and all people who contributed to that lib.
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## Future
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#### Must
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- elaborate performance connected state.
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#### Should
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- add examples
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- investigate performance gain of no CRC.
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#### Could
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#### Wont
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- unit tests
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- get it working is too time consuming.
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