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98 lines
4.5 KiB
98 lines
4.5 KiB
# esp32-ds18b20
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## Introduction
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This is a ESP32-compatible C component for the Maxim Integrated DS18B20 Programmable Resolution 1-Wire Digital
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Thermometer device.
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It supports multiple devices on the same 1-Wire bus.
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It is written and tested for v2.1, v3.0-3.3 and v4.1-beta1 of the [ESP-IDF](https://github.com/espressif/esp-idf)
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environment, using the xtensa-esp32-elf toolchain (gcc version 5.2.0).
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## Dependencies
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Requires [esp32-owb](https://github.com/DavidAntliff/esp32-owb).
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## Example
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See [esp32-ds18b20-example](https://github.com/DavidAntliff/esp32-ds18b20-example) for an example that supports single
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and multiple devices on a single bus.
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## Features
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In cooperation with the underlying esp32-owb component, this component includes:
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* External power supply mode.
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* Parasitic power mode (VDD and GND connected) - see notes below.
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* Static (stack-based) or dynamic (malloc-based) memory model.
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* No globals - support any number of DS18B20 devices on any number of 1-Wire buses simultaneously.
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* 1-Wire device detection and validation, including search for multiple devices on a single bus.
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* Addressing optimisation for a single (solo) device on a bus.
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* CRC checks on temperature data.
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* Programmable temperature measurement resolution (9, 10, 11 or 12-bit resolution).
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* Temperature conversion and retrieval.
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* Separation of conversion and temperature retrieval to allow for simultaneous conversion across multiple devices.
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## Parasitic Power Mode
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Consult the [datasheet](http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf) for more detailed information about
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Parasitic Power mode.
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Parasitic power operation can be detected by `ds18b20_check_for_parasite_power()` followed by a call to
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`owb_use_parasitic_power()`, or simply set explicitly by a call to the latter.
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This library has been tested on the ESP32 with two parasitic-power configurations, with two DS18B20 devices at 3.3V:
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1. Disconnect power to each device's VDD pin, and connect that pin to GND for each device. Power is supplied to
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each device through the OWB data line.
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2. Connect the OWB data line to VCC via a P-channel MOSFET (e.g. BS250) and current-limiting resistor (e.g. 270 Ohm).
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Ensure your code calls `owb_use_strong_pullup_gpio()` with the GPIO connected to the MOSFET Gate. The GPIO will go
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high during temperature conversion, turning on the MOSFET and providing power from VCC to each device through the OWB
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data line.
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If you set up configuration 1 and do not see CRC errors, but you get incorrect temperature readings around 80 - 85
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degrees C, then it is likely that your DS18B20 devices are running out of power during the temperature conversion. In
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this case, consider reducing the value of the pull-up resistor. For example, I have had success obtaining correct
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conversions from two parasitic DS18B20 devices by replacing the 4k7 Ohm pull-up resistor with a 1 kOhm resistor.
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Alternatively, consider using configuration 2.
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Note that use of parasitic power mode disables the ability for devices on the bus to signal that an operation has
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completed. This means that DS18B20 devices in parasitic power mode are not able to communicate when they have completed
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a temperature conversion. In this mode, a delay for a pre-calculated duration occurs, and then the conversion result is
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read from the device(s). *If your ESP32 is not running on the correct clock rate, this duration may be too short!*
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## Documentation
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Automatically generated API documentation (doxygen) is available [here](https://davidantliff.github.io/esp32-ds18b20/index.html).
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## Source Code
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The source is available from [GitHub](https://www.github.com/DavidAntliff/esp32-ds18b20).
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## License
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The code in this project is licensed under the MIT license - see LICENSE for details.
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## Links
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* [DS18B20 Datasheet](http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf)
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* [1-Wire Communication Through Software](https://www.maximintegrated.com/en/app-notes/index.mvp/id/126)
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* [1-Wire Search Algorithm](https://www.maximintegrated.com/en/app-notes/index.mvp/id/187)
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* [Espressif IoT Development Framework for ESP32](https://github.com/espressif/esp-idf)
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## Acknowledgements
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Parts of this code are based on references provided to the public domain by Maxim Integrated.
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"1-Wire" is a registered trademark of Maxim Integrated.
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## Roadmap
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The following features are anticipated but not yet implemented:
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* Concurrency support (multiple tasks accessing devices on the same bus).
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* Alarm support.
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* EEPROM support.
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* Parasitic power support.
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