forked from electro/esp-irblaster
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
99 lines
4.5 KiB
99 lines
4.5 KiB
2 years ago
|
# esp32-ds18b20
|
||
|
|
|
||
|
|
## Introduction
|
||
|
|
|
||
|
|
This is a ESP32-compatible C component for the Maxim Integrated DS18B20 Programmable Resolution 1-Wire Digital
|
||
|
|
Thermometer device.
|
||
|
|
|
||
|
|
It supports multiple devices on the same 1-Wire bus.
|
||
|
|
|
||
|
|
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)
|
||
|
|
environment, using the xtensa-esp32-elf toolchain (gcc version 5.2.0).
|
||
|
|
|
||
|
|
## Dependencies
|
||
|
|
|
||
|
|
Requires [esp32-owb](https://github.com/DavidAntliff/esp32-owb).
|
||
|
|
|
||
|
|
## Example
|
||
|
|
|
||
|
|
See [esp32-ds18b20-example](https://github.com/DavidAntliff/esp32-ds18b20-example) for an example that supports single
|
||
|
|
and multiple devices on a single bus.
|
||
|
|
|
||
|
|
## Features
|
||
|
|
|
||
|
|
In cooperation with the underlying esp32-owb component, this component includes:
|
||
|
|
|
||
|
|
* External power supply mode.
|
||
|
|
* Parasitic power mode (VDD and GND connected) - see notes below.
|
||
|
|
* Static (stack-based) or dynamic (malloc-based) memory model.
|
||
|
|
* No globals - support any number of DS18B20 devices on any number of 1-Wire buses simultaneously.
|
||
|
|
* 1-Wire device detection and validation, including search for multiple devices on a single bus.
|
||
|
|
* Addressing optimisation for a single (solo) device on a bus.
|
||
|
|
* CRC checks on temperature data.
|
||
|
|
* Programmable temperature measurement resolution (9, 10, 11 or 12-bit resolution).
|
||
|
|
* Temperature conversion and retrieval.
|
||
|
|
* Separation of conversion and temperature retrieval to allow for simultaneous conversion across multiple devices.
|
||
|
|
|
||
|
|
## Parasitic Power Mode
|
||
|
|
|
||
|
|
Consult the [datasheet](http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf) for more detailed information about
|
||
|
|
Parasitic Power mode.
|
||
|
|
|
||
|
|
Parasitic power operation can be detected by `ds18b20_check_for_parasite_power()` followed by a call to
|
||
|
|
`owb_use_parasitic_power()`, or simply set explicitly by a call to the latter.
|
||
|
|
|
||
|
|
This library has been tested on the ESP32 with two parasitic-power configurations, with two DS18B20 devices at 3.3V:
|
||
|
|
|
||
|
|
1. Disconnect power to each device's VDD pin, and connect that pin to GND for each device. Power is supplied to
|
||
|
|
each device through the OWB data line.
|
||
|
|
2. Connect the OWB data line to VCC via a P-channel MOSFET (e.g. BS250) and current-limiting resistor (e.g. 270 Ohm).
|
||
|
|
Ensure your code calls `owb_use_strong_pullup_gpio()` with the GPIO connected to the MOSFET Gate. The GPIO will go
|
||
|
|
high during temperature conversion, turning on the MOSFET and providing power from VCC to each device through the OWB
|
||
|
|
data line.
|
||
|
|
|
||
|
|
If you set up configuration 1 and do not see CRC errors, but you get incorrect temperature readings around 80 - 85
|
||
|
|
degrees C, then it is likely that your DS18B20 devices are running out of power during the temperature conversion. In
|
||
|
|
this case, consider reducing the value of the pull-up resistor. For example, I have had success obtaining correct
|
||
|
|
conversions from two parasitic DS18B20 devices by replacing the 4k7 Ohm pull-up resistor with a 1 kOhm resistor.
|
||
|
|
|
||
|
|
Alternatively, consider using configuration 2.
|
||
|
|
|
||
|
|
Note that use of parasitic power mode disables the ability for devices on the bus to signal that an operation has
|
||
|
|
completed. This means that DS18B20 devices in parasitic power mode are not able to communicate when they have completed
|
||
|
|
a temperature conversion. In this mode, a delay for a pre-calculated duration occurs, and then the conversion result is
|
||
|
|
read from the device(s). *If your ESP32 is not running on the correct clock rate, this duration may be too short!*
|
||
|
|
|
||
|
|
## Documentation
|
||
|
|
|
||
|
|
Automatically generated API documentation (doxygen) is available [here](https://davidantliff.github.io/esp32-ds18b20/index.html).
|
||
|
|
|
||
|
|
## Source Code
|
||
|
|
|
||
|
|
The source is available from [GitHub](https://www.github.com/DavidAntliff/esp32-ds18b20).
|
||
|
|
|
||
|
|
## License
|
||
|
|
|
||
|
|
The code in this project is licensed under the MIT license - see LICENSE for details.
|
||
|
|
|
||
|
|
## Links
|
||
|
|
|
||
|
|
* [DS18B20 Datasheet](http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf)
|
||
|
|
* [1-Wire Communication Through Software](https://www.maximintegrated.com/en/app-notes/index.mvp/id/126)
|
||
|
|
* [1-Wire Search Algorithm](https://www.maximintegrated.com/en/app-notes/index.mvp/id/187)
|
||
|
|
* [Espressif IoT Development Framework for ESP32](https://github.com/espressif/esp-idf)
|
||
|
|
|
||
|
|
## Acknowledgements
|
||
|
|
|
||
|
|
Parts of this code are based on references provided to the public domain by Maxim Integrated.
|
||
|
|
|
||
|
|
"1-Wire" is a registered trademark of Maxim Integrated.
|
||
|
|
|
||
|
|
## Roadmap
|
||
|
|
|
||
|
|
The following features are anticipated but not yet implemented:
|
||
|
|
|
||
|
|
* Concurrency support (multiple tasks accessing devices on the same bus).
|
||
|
|
* Alarm support.
|
||
|
|
* EEPROM support.
|
||
|
|
* Parasitic power support.
|