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86 lines
3.3 KiB
Markdown
86 lines
3.3 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DS1821/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DS1821/releases)
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# DS1821
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Arduino library for DS1821 temperature sensor (experimental)
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## Description
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The DS1821 is a temperature sensor that uses the oneWire protocol.
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This library supports one sensor per pin.
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As this library is tested minimally please consider it experimental.
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The sensor is hard to get however still available on internet.
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## Interface (temperature sensor)
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The interface of the library is an async interface so there are no blocking calls.
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The return value **DS1821_RESET_ERROR == -999** means that the oneWire bus failed to reset.
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- **DS1821(onewire)** initializes the library with a reference to a oneWire object.
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See examples.
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- **int requestTemperature()** this call will trigger a conversion of temperature,
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however it does not read the temperature. May return **DS1821_RESET_ERROR**
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- **int conversionReady()** when the conversion is ready it returns 1, else 0.
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May return **DS1821_RESET_ERROR**
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- **float readTemperature()** when conversion is ready, one can fetch the temperature.
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May return **DS1821_RESET_ERROR**
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- **int error()** read the last error.
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The low / high functions can be used to monitor if a threshold has been exceeded
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between reads of the temperature.
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- **setLow(lo)** set low (OFF) threshold temperature
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- **getLow()** read back from config
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- **setHigh(hi)** set high (ON) threshold temperature
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- **getHigh()** read back from config.
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- **getHighFlag()** flag is set if temperature has exceeded high threshold.
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- **clrHighFlag()** reset the high threshold flag
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- **getLowFlag()** flag is set if temperature has exceeded low threshold.
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- **clrLowFlag()** reset the low threshold flag
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## Interface (thermostat)
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Please read datasheet.
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The DS1821 can be setup as a standalone thermostat with a high level and low level.
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In this mode the DS1821 uses the **DQ** pin to switch a device ON when the high level
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is exceeded and switches OFF when the low level is reached.
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This prevents too frequent toggling which would happen if only one temperature was used.
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To configure the thermostat mode please check the example.
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The library provides the following functions for configuring the Thermostat mode
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- **setOneWireMode(VDD, DQ)**
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This function puts a DS1821 in Thermostat mode back into oneWire mode.
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DQ must be the same as oneWire(pin).
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VDD is the voltage controlling pin of the sensor.
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- **setThermostatMode()** sets the flag in the config register to start in
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Thermostat mode next restart.
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The polarity functions are also available in temperature sensor mode,
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however they have no effect in that mode.
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- **setPolarity(activstate)** When in thermostat mode the DQ pin controls e.g.
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a fan or a motor. Activstate defines which value is ON and OFF.
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- **getPolarity()** reads back polarity from the device.
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The Low / High values set in sensor mode gives the DS1821 the thresholds
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to toggle the DQ line in the thermostat mode.
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## Future
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- Get new sensors to test test test...
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- merge clrLowFlag() into getLowFlag() ? high idem?
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-
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## Operation
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See examples.
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