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135 lines
5.1 KiB
Markdown
135 lines
5.1 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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## Interface
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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)** constructor needs a reference to OneWire object.
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- **bool begin(uint8_t retries = 3)** resets oneWire and set resolution to 9 bit.
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returns true if all is OK. 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
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-127 = DEVICE_DISCONNECTED
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- **void setResolution(uint8_t resolution = 9)** resolution = 9..12 (9 is default)
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- **bool getAddress()** returns true if the sensor is configured (available)
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This allowed the class to be both minimal in size and non-blocking. In fact the class
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has no support for a synchronous read in one call. This choice will teach people
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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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## 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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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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Check examples.
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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 |
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|--------------:|------------:|-----------:|
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| 10cm (4") | 10K0 | 6K8 |
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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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- unit tests
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- add constants
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- get it working
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